Fixed readme again

Update oraxen dependency

CONTRIBUTING.md

@@ -1,38 +1,7 @@
 # How to contribute to eco
 
-## Codestyle
+Please open any Pull Requests into the `develop` branch or ideally into a new branch for your changes. PRs that go into `master` won't be ignored, but I have to checkout and merge manually, which makes your PR show as being closed.
 
-1. The eco checkstyle is in /config/checkstyle.xml
+Do not write any Kotlin-only APIs; all API components should be written in Java, Kotlin extensions should not have functionality that isn't available in java. The same applies the other way round, do not write any backend code in Java, it should be Kotlin-exclusive.
 
-- The pull request must not have any checkstyle issues.
-- Every method and field must have a javadoc attached.
-
-2. Use JetBrains annotations
-
-- Every parameter should be annotated with @NotNull or @Nullable
-
-3. Imports
-
-- No group (*) imports.
-- No static imports.
-
-4. Kotlin
-
-- Kotlin should be the only language used in the backend, java should be the only language used in the frontend.
-- Kotlin API extensions should only be for creating extension functions and extra niceties that aren't possible in java.
-  Do not write API components in kotlin.
-- Kotlin code should never be called directly from the frontend Java API. Kotlin API extensions should always rely on
-  java, not the other way round.
-
-## Dependency Injection
-
-- eco uses Dependency Injection
-- Any calls to Eco#getHandler#getEcoPlugin are code smells and should never be used unless **absolutely necessary**.
-- NamespacedKeys, FixedMetadataValues, Runnables, and Schedules should be managed using AbstractEcoPlugin through DI.
-- Any DI class should extend PluginDependent where possible. If the class extends another, then you **must** store the
-  plugin instance in a private final variable called **plugin** with a private or protected getter.
-
-## Other
-
-- All drops **must** be sent through a DropQueue - calls to World#dropItem will get your PR rejected.
-- eco is built with java 17.
+If you have any questions about contributing, feel free to ask in the [Discord](https://discord.gg/ZcwpSsE)!

README.md

@@ -1,5 +1,5 @@
 # eco
-eco is a powerful Spigot development library that simplifies the process of plugin creation and supercharges
+eco is a powerful Spigot plugin framework that simplifies the process of plugin creation and supercharges
 your plugins.
 It's the engine behind [EcoEnchants](https://polymart.org/resource/490), [Reforges](https://polymart.org/resource/1330),
 [EcoItems](https://polymart.org/resource/1247), [EcoSkills](https://polymart.org/resource/1351),
@@ -16,30 +16,54 @@ and many more.
     <a href="https://bstats.org/plugin/bukkit/EcoEnchants" alt="bstats players">
         <img src="https://img.shields.io/bstats/players/7666?color=informational"/>
     </a>
-    <a href="https://plugins.auxilor.io/" alt="Docs (gitbook)">
-        <img src="https://img.shields.io/badge/docs-gitbook-informational"/>
-    </a>
     <a href="https://discord.gg/ZcwpSsE/" alt="Discord">
         <img src="https://img.shields.io/discord/452518336627081236?label=discord&color=informational"/>
     </a>
     <a href="https://github.com/Auxilor/eco/actions/workflows/java-ci.yml" alt="Latest Dev Build">
-        <img src="https://img.shields.io/github/workflow/status/Auxilor/eco/Java%20CI/develop?color=informational"/>
+        <img src="https://img.shields.io/github/actions/workflow/status/Auxilor/eco/java-ci.yml?branch=develop&color=informational"/>
     </a>
 </p>
 
+eco comes packed with all the tools you need in your plugins:
+
+- Modern command API
+- Native color parsing with full hex/RGB/MiniMessage support
+- Yaml/JSON/TOML config system
+- Persistent data storage API with Yaml/MySQL/MongoDB support
+- Packet item display system
+- Lightweight event loop based packet API
+- Entity AI API with near-1:1 NMS mappings
+- More events
+- Extension API, essentially plugins for plugins
+- Fluent dependency injection for NamespacedKey, Metadata values, etc.
+- Ultra-fast ItemStack reimplementation bypassing ItemMeta
+- Complete GUI API with pre-made components available from [ecomponent](https://github.com/Auxilor/ecomponent)
+- Over 30 native integrations for other plugins
+- First-class custom item support with lookup strings
+- Math expression parsing via [Crunch](https://github.com/Redempt/Crunch)
+- Particle lookups
+- Complete Placeholder API
+- Price system, supporting economy plugins, XP, Items, etc.
+- NMS/Version-specific tooling
+- Custom crafting recipe API with support for stacks and custom items
+- Native plugin update checking
+- Native bStats support
+- Full Kotlin support and native extensions
+- Tooling to make meta-frameworks, like [libreforge](https://github.com/Auxilor/libreforge)
+- And much more
+
 # For server owners
-- Requires ProtocolLib to be installed: get the latest version [here](https://www.spigotmc.org/resources/protocollib.1997/)
 - Supports 1.17+
 
 ## Downloads
 
-- Stable (Recommended): [GitHub](https://github.com/Auxilor/eco/releases), [Polymart](https://polymart.org/resource/eco.773)
-- Dev (Not Recommended): [GitHub](https://github.com/Auxilor/eco/actions/workflows/java-ci.yml) (Open latest run and download)
+- Stable: [GitHub](https://github.com/Auxilor/eco/releases), [Polymart](https://polymart.org/resource/eco.773)
+- Dev: [GitHub](https://github.com/Auxilor/eco/actions/workflows/java-ci.yml) (Open latest run and download)
 
 # For developers
 
 ## Javadoc
-The 6.45.0 Javadoc can be found [here](https://javadoc.jitpack.io/com/willfp/eco/6.45.0/javadoc/)
+The 6.49.0 Javadoc can be found [here](https://javadoc.jitpack.io/com/willfp/eco/6.49.0/javadoc/)
 
 ## Plugin Information
 
@@ -68,7 +92,7 @@ dependencies {
 }
 ```
 
-Replace `Tag` with a release tag for eco, eg `6.45.0`.
+Replace `Tag` with a release tag for eco, eg `6.49.0`.
 
 Maven:
 
@@ -88,7 +112,7 @@ Maven:
 </dependency>
 ```
 
-Replace `Tag` with a release tag for eco, eg `6.45.0`.
+Replace `Tag` with a release tag for eco, eg `6.49.0`.
 
 ## Build locally:
 
@@ -103,7 +127,7 @@ cd eco
 
 ## License
 
-*Click here to read [the entire license](https://github.com/Auxilor/eco/blob/master/LICENSE.md).*
+eco is licensed under GNU GPL3. *Click here to read [the entire license](https://github.com/Auxilor/eco/blob/master/LICENSE.md).*
 
 <h1 align="center">
   Check out our partners!

build.gradle.kts

@@ -25,6 +25,7 @@ dependencies {
     implementation(project(path = ":eco-core:core-nms:v1_18_R1", configuration = "reobf"))
     implementation(project(path = ":eco-core:core-nms:v1_18_R2", configuration = "reobf"))
     implementation(project(path = ":eco-core:core-nms:v1_19_R1", configuration = "reobf"))
+    implementation(project(path = ":eco-core:core-nms:v1_19_R2", configuration = "reobf"))
 }
 
 allprojects {
@@ -77,6 +78,8 @@ allprojects {
 
         // LibsDisguises
         maven("https://repo.md-5.net/content/groups/public/")
+
+        maven("https://repo.techscode.com/repository/maven-releases/")
     }
 
     dependencies {

eco-api/src/main/java/com/willfp/eco/core/AbstractPacketAdapter.java

@@ -13,27 +13,30 @@ import java.util.Collections;
 
 /**
  * Wrapper class for ProtocolLib packets.
+ *
+ * @deprecated ProtocolLib is no longer used by eco. Use {@link com.willfp.eco.core.packet.PacketListener} instead.
  */
+@Deprecated(since = "6.51.0")
 public abstract class AbstractPacketAdapter extends PacketAdapter {
     /**
-     * The packet type to listen for.
+     * The handle type to listen for.
      */
     private final PacketType type;
 
     /**
-     * Whether the packet adapter should be registered after the server has loaded.
+     * Whether the handle adapter should be registered after the server has loaded.
      * <p>
      * Useful for monitor priority adapters that <b>must</b> be ran last.
      */
     private final boolean postLoad;
 
     /**
-     * Create a new packet adapter for a specified plugin and type.
+     * Create a new handle adapter for a specified plugin and type.
      *
      * @param plugin   The plugin that ProtocolLib should mark as the owner.
      * @param type     The {@link PacketType} to listen for.
-     * @param priority The priority at which the adapter should be ran on packet send/receive.
-     * @param postLoad If the packet adapter should be registered after the server has loaded.
+     * @param priority The priority at which the adapter should be ran on handle send/receive.
+     * @param postLoad If the handle adapter should be registered after the server has loaded.
      */
     protected AbstractPacketAdapter(@NotNull final EcoPlugin plugin,
                                     @NotNull final PacketType type,
@@ -45,11 +48,11 @@ public abstract class AbstractPacketAdapter extends PacketAdapter {
     }
 
     /**
-     * Create a new packet adapter for a specified plugin and type.
+     * Create a new handle adapter for a specified plugin and type.
      *
      * @param plugin   The plugin that ProtocolLib should mark as the owner.
      * @param type     The {@link PacketType} to listen for.
-     * @param postLoad If the packet adapter should be registered after the server has loaded.
+     * @param postLoad If the handle adapter should be registered after the server has loaded.
      */
     protected AbstractPacketAdapter(@NotNull final EcoPlugin plugin,
                                     @NotNull final PacketType type,
@@ -58,9 +61,9 @@ public abstract class AbstractPacketAdapter extends PacketAdapter {
     }
 
     /**
-     * The code that should be executed once the packet has been received.
+     * The code that should be executed once the handle has been received.
      *
-     * @param packet The packet.
+     * @param packet The handle.
      * @param player The player.
      * @param event  The event.
      */
@@ -71,9 +74,9 @@ public abstract class AbstractPacketAdapter extends PacketAdapter {
     }
 
     /**
-     * THe code that should be executed once the packet has been sent.
+     * THe code that should be executed once the handle has been sent.
      *
-     * @param packet The packet.
+     * @param packet The handle.
      * @param player The player.
      * @param event  The event.
      */
@@ -84,7 +87,7 @@ public abstract class AbstractPacketAdapter extends PacketAdapter {
     }
 
     /**
-     * Boilerplate to assert that the packet is of the specified type.
+     * Boilerplate to assert that the handle is of the specified type.
      *
      * @param event The ProtocolLib event.
      */
@@ -102,7 +105,7 @@ public abstract class AbstractPacketAdapter extends PacketAdapter {
     }
 
     /**
-     * Boilerplate to assert that the packet is of the specified type.
+     * Boilerplate to assert that the handle is of the specified type.
      *
      * @param event The ProtocolLib event.
      */
@@ -125,7 +128,7 @@ public abstract class AbstractPacketAdapter extends PacketAdapter {
     }
 
     /**
-     * Register the packet adapter with ProtocolLib.
+     * Register the handle adapter with ProtocolLib.
      */
     public final void register() {
         if (!ProtocolLibrary.getProtocolManager().getPacketListeners().contains(this)) {
@@ -134,7 +137,7 @@ public abstract class AbstractPacketAdapter extends PacketAdapter {
     }
 
     /**
-     * Get if the packet adapter should be loaded last.
+     * Get if the handle adapter should be loaded last.
      *
      * @return If post load.
      */

eco-api/src/main/java/com/willfp/eco/core/Eco.java

@@ -1,5 +1,8 @@
 package com.willfp.eco.core;
 
+import com.willfp.eco.core.command.CommandBase;
+import com.willfp.eco.core.command.PluginCommandBase;
+import com.willfp.eco.core.command.impl.PluginCommand;
 import com.willfp.eco.core.config.ConfigType;
 import com.willfp.eco.core.config.interfaces.Config;
 import com.willfp.eco.core.config.interfaces.LoadableConfig;
@@ -23,6 +26,7 @@ import com.willfp.eco.core.gui.slot.SlotBuilder;
 import com.willfp.eco.core.gui.slot.functional.SlotProvider;
 import com.willfp.eco.core.items.TestableItem;
 import com.willfp.eco.core.math.MathContext;
+import com.willfp.eco.core.packet.Packet;
 import com.willfp.eco.core.proxy.ProxyFactory;
 import com.willfp.eco.core.scheduling.Scheduler;
 import net.kyori.adventure.platform.bukkit.BukkitAudiences;
@@ -47,18 +51,18 @@ import java.util.UUID;
 import java.util.logging.Logger;
 
 /**
- * Holds the instance of eco for bridging between the frontend
- * and backend.
+ * Holds the instance of eco for bridging between the frontend and backend.
  * <p>
  * <strong>Do not use this in your plugins!</strong> It can and will contain
- * breaking changes between minor versions and even patches, and you will create
- * compatibility issues by. All parts of this have been abstracted
- * into logically named API components that you can use.
+ * breaking changes between minor versions and even patches, and you will create compatibility
+ * issues by. All parts of this have been abstracted into logically named API components that you
+ * can use.
  *
  * @see Eco#get()
  */
 @ApiStatus.Internal
 public interface Eco {
+
     /**
      * Create a scheduler.
      *
@@ -71,7 +75,7 @@ public interface Eco {
     /**
      * Create an event manager.
      *
-     * @param plugin The plugin.
+     * @param plugin The plugin.F
      * @return The event manager.
      */
     @NotNull
@@ -155,6 +159,40 @@ public interface Eco {
     @NotNull
     EcoPlugin getEcoPlugin();
 
+    /**
+     * Create PluginCommandBase implementation of {@link PluginCommand}.
+     *
+     * @param parentDelegate the enclosing class of this implementation.
+     * @param plugin         the plugin.
+     * @param name           the name of the command.
+     * @param permission     the permission of the command.
+     * @param playersOnly    if the command is players only.
+     * @return The PluginCommandBase implementation
+     */
+    @NotNull
+    PluginCommandBase createPluginCommand(@NotNull CommandBase parentDelegate,
+                                          @NotNull EcoPlugin plugin,
+                                          @NotNull String name,
+                                          @NotNull String permission,
+                                          boolean playersOnly);
+
+    /**
+     * Create CommandBase implementation of {@link com.willfp.eco.core.command.impl.Subcommand Subcommand}.
+     *
+     * @param parentDelegate the enclosing class of this implementation.
+     * @param plugin         the plugin.
+     * @param name           the name of the command.
+     * @param permission     the permission of the command.
+     * @param playersOnly    if the command is players only.
+     * @return The CommandBase implementation
+     */
+    @NotNull
+    CommandBase createSubcommand(@NotNull CommandBase parentDelegate,
+                                 @NotNull EcoPlugin plugin,
+                                 @NotNull String name,
+                                 @NotNull String permission,
+                                 boolean playersOnly);
+
     /**
      * Updatable config.
      *
@@ -376,9 +414,8 @@ public interface Eco {
     /**
      * Create a {@link NamespacedKey} quickly
      * <p>
-     * Bypasses the constructor, allowing for the creation of invalid keys,
-     * therefore this is considered unsafe and should only be called after
-     * the key has been confirmed to be valid.
+     * Bypasses the constructor, allowing for the creation of invalid keys, therefore this is
+     * considered unsafe and should only be called after the key has been confirmed to be valid.
      *
      * @param namespace The namespace.
      * @param key       The key.
@@ -511,8 +548,23 @@ public interface Eco {
     void syncCommands();
 
     /**
-     * Get the instance of eco; the bridge between the api frontend
-     * and the implementation backend.
+     * Unregister a command.
+     *
+     * @param command The command.
+     */
+    void unregisterCommand(@NotNull PluginCommandBase command);
+
+    /**
+     * Send a packet.
+     *
+     * @param player The player.
+     * @param packet The packet.
+     */
+    void sendPacket(@NotNull Player player,
+                    @NotNull Packet packet);
+
+    /**
+     * Get the instance of eco; the bridge between the api frontend and the implementation backend.
      *
      * @return The instance of eco.
      */
@@ -526,6 +578,7 @@ public interface Eco {
      */
     @ApiStatus.Internal
     final class Instance {
+
         /**
          * Instance of eco.
          */

eco-api/src/main/java/com/willfp/eco/core/EcoPlugin.java

@@ -13,6 +13,7 @@ import com.willfp.eco.core.factory.MetadataValueFactory;
 import com.willfp.eco.core.factory.NamespacedKeyFactory;
 import com.willfp.eco.core.factory.RunnableFactory;
 import com.willfp.eco.core.integrations.IntegrationLoader;
+import com.willfp.eco.core.packet.PacketListener;
 import com.willfp.eco.core.proxy.ProxyFactory;
 import com.willfp.eco.core.scheduling.Scheduler;
 import com.willfp.eco.core.web.UpdateChecker;
@@ -52,7 +53,7 @@ import java.util.stream.Collectors;
  * <b>IMPORTANT: When reloading a plugin, all runnables / tasks will
  * be cancelled.</b>
  */
-@SuppressWarnings("unused")
+@SuppressWarnings({"unused", "DeprecatedIsStillUsed", "deprecation", "RedundantSuppression"})
 public abstract class EcoPlugin extends JavaPlugin implements PluginLike {
     /**
      * The polymart resource ID of the plugin.
@@ -344,6 +345,13 @@ public abstract class EcoPlugin extends JavaPlugin implements PluginLike {
         this.configHandler = Eco.get().createConfigHandler(this);
 
         this.langYml = this.createLangYml();
+
+        if (!this.langYml.isValid() && !(this instanceof Eco)) {
+            this.getLogger().warning("Notify plugin authors " + String.join(", ", this.getDescription().getAuthors()) + " that");
+            this.getLogger().warning("they are missing crucial lang.yml keys! They can be found");
+            this.getLogger().warning("in the LangYml class.");
+        }
+
         this.configYml = this.createConfigYml();
 
         Eco.get().addNewPlugin(this);
@@ -415,13 +423,16 @@ public abstract class EcoPlugin extends JavaPlugin implements PluginLike {
 
         Prerequisite.update();
 
+        if (Prerequisite.HAS_PROTOCOLLIB.isMet()) {
             this.loadPacketAdapters().forEach(abstractPacketAdapter -> {
                 if (!abstractPacketAdapter.isPostLoad()) {
                     abstractPacketAdapter.register();
                 }
             });
+        }
 
         this.loadListeners().forEach(listener -> this.getEventManager().registerListener(listener));
+        this.loadPacketListeners().forEach(listener -> this.getEventManager().registerPacketListener(listener));
 
         this.loadPluginCommands().forEach(PluginCommand::register);
 
@@ -513,11 +524,13 @@ public abstract class EcoPlugin extends JavaPlugin implements PluginLike {
             Display.registerDisplayModule(this.getDisplayModule());
         }
 
+        if (Prerequisite.HAS_PROTOCOLLIB.isMet()) {
             this.loadPacketAdapters().forEach(abstractPacketAdapter -> {
                 if (abstractPacketAdapter.isPostLoad()) {
                     abstractPacketAdapter.register();
                 }
             });
+        }
 
         if (!Prerequisite.HAS_PAPER.isMet()) {
             this.getLogger().severe("");
@@ -674,16 +687,27 @@ public abstract class EcoPlugin extends JavaPlugin implements PluginLike {
     }
 
     /**
-     * ProtocolLib packet adapters to be registered.
+     * ProtocolLib handle adapters to be registered.
      * <p>
      * If the plugin does not require ProtocolLib this can be left empty.
      *
-     * @return A list of packet adapters.
+     * @return A list of handle adapters.
+     * @deprecated Use {@link #loadPacketListeners()} instead.
      */
+    @Deprecated(since = "6.51.0")
     protected List<AbstractPacketAdapter> loadPacketAdapters() {
         return new ArrayList<>();
     }
 
+    /**
+     * Packet Listeners to be registered.
+     *
+     * @return A list of handle listeners.
+     */
+    protected List<PacketListener> loadPacketListeners() {
+        return new ArrayList<>();
+    }
+
     /**
      * All listeners to be registered.
      *
@@ -699,7 +723,15 @@ public abstract class EcoPlugin extends JavaPlugin implements PluginLike {
      * @return lang.yml.
      */
     protected LangYml createLangYml() {
+        try {
             return new LangYml(this);
+        } catch (NullPointerException e) {
+            this.getLogger().severe("Failed to load lang.yml!");
+            this.getLogger().severe("For the developer of this plugin: make sure you have a lang.yml");
+            e.printStackTrace();
+            Bukkit.getPluginManager().disablePlugin(this);
+            return null;
+        }
     }
 
     /**
@@ -710,7 +742,15 @@ public abstract class EcoPlugin extends JavaPlugin implements PluginLike {
      * @return config.yml.
      */
     protected ConfigYml createConfigYml() {
+        try {
             return new ConfigYml(this);
+        } catch (NullPointerException e) {
+            this.getLogger().severe("Failed to load config.yml!");
+            this.getLogger().severe("For the developer of this plugin: make sure you have a config.yml");
+            e.printStackTrace();
+            Bukkit.getPluginManager().disablePlugin(this);
+            return null;
+        }
     }
 
     /**

eco-api/src/main/java/com/willfp/eco/core/PluginProps.java

@@ -221,7 +221,7 @@ public final class PluginProps {
 
     /**
      * Create new props from known values.
-     *
+     * <p>
      * Marked as internal as this method will break whenever the properties themselves
      * are updated (e.g. if a new property is added) - so to prevent any potential
      * backwards-compatibility bugs, this method cannot be invoked outside eco itself.

eco-api/src/main/java/com/willfp/eco/core/Prerequisite.java

@@ -30,6 +30,14 @@ public class Prerequisite {
             "Requires server to be running paper (or a fork)"
     );
 
+    /**
+     * Requires the server to be running an implementation of paper.
+     */
+    public static final Prerequisite HAS_PROTOCOLLIB = new Prerequisite(
+            () -> ClassUtils.exists("com.comphenix.protocol.events.PacketAdapter"),
+            "Requires server to have ProtocolLib"
+    );
+
     /**
      * Requires the server to have vault installed.
      *
@@ -70,7 +78,10 @@ public class Prerequisite {
 
     /**
      * Requires the server to be running an implementation of BungeeCord.
+     *
+     * @deprecated This will never return true.
      */
+    @Deprecated(since = "6.49.0", forRemoval = true)
     public static final Prerequisite HAS_BUNGEECORD = new Prerequisite(
             () -> ClassUtils.exists("net.md_5.bungee.api.event.ServerConnectedEvent"),
             "Requires server to be running BungeeCord (or a fork)"
@@ -78,7 +89,10 @@ public class Prerequisite {
 
     /**
      * Requires the server to be running an implementation of Velocity.
+     *
+     * @deprecated This will never return true.
      */
+    @Deprecated(since = "6.49.0", forRemoval = true)
     public static final Prerequisite HAS_VELOCITY = new Prerequisite(
             () -> ClassUtils.exists("com.velocitypowered.api.event.player.ServerConnectedEvent"),
             "Requires server to be running Velocity (or a fork)"

eco-api/src/main/java/com/willfp/eco/core/command/CommandBase.java

@@ -1,32 +1,37 @@
 package com.willfp.eco.core.command;
 
-import com.google.common.collect.ImmutableList;
 import com.willfp.eco.core.EcoPlugin;
+import org.bukkit.Bukkit;
+import org.bukkit.OfflinePlayer;
 import org.bukkit.command.CommandSender;
 import org.bukkit.entity.Player;
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Objects;
+import java.util.function.Predicate;
 
 /**
- * Interface for all command implementations.
+ * Generic interface for commands.
  */
-@SuppressWarnings("removal")
+@SuppressWarnings("null")
 public interface CommandBase {
+
     /**
      * Get command name.
      *
      * @return The name.
      */
-    String getName();
+    @NotNull String getName();
 
     /**
      * Get command permission.
      *
      * @return The permission.
      */
-    String getPermission();
+    @NotNull String getPermission();
 
     /**
      * If only players can execute the command.
@@ -41,110 +46,237 @@ public interface CommandBase {
      * @param command The subcommand.
      * @return The parent command.
      */
-    CommandBase addSubcommand(@NotNull CommandBase command);
+    @NotNull CommandBase addSubcommand(@NotNull CommandBase command);
+
+    /**
+     * Get the subcommands of the command.
+     *
+     * @return The subcommands.
+     */
+    @NotNull List<CommandBase> getSubcommands();
+
+    /**
+     * Intended for returning the enclosing CommandBase,
+     * when this instance is serving as the delegate command base.
+     *
+     * @return the wrapping object of this delegate.
+     */
+    default @NotNull CommandBase getWrapped() {
+        return this;
+    }
 
     /**
      * Handle command execution.
+     * <p>
+     * This will always be called on command execution.
      *
      * @param sender The sender.
      * @param args   The args.
+     * @throws NotificationException naturally, this is handled as a part of the command system.
      */
-    default void onExecute(@NotNull CommandSender sender,
-                           @NotNull List<String> args) {
+    default void onExecute(@NotNull final CommandSender sender, @NotNull final List<String> args) throws NotificationException {
         // Do nothing.
     }
 
     /**
      * Handle command execution from players.
+     * <p>
+     * This will only be called if the sender is a player.
      *
      * @param sender The sender.
      * @param args   The args.
+     * @throws NotificationException naturally, this is handled as a part of the command system.
      */
-    default void onExecute(@NotNull Player sender,
-                           @NotNull List<String> args) {
+    default void onExecute(@NotNull final Player sender, @NotNull final List<String> args) throws NotificationException {
         // Do nothing.
     }
 
     /**
      * Handle tab completion.
+     * <p>
+     * This will always be called on tab completion.
      *
      * @param sender The sender.
      * @param args   The args.
      * @return The results.
      */
     @NotNull
-    default List<String> tabComplete(@NotNull CommandSender sender,
-                                     @NotNull List<String> args) {
+    default List<String> tabComplete(@NotNull final CommandSender sender, @NotNull final List<String> args) {
         return new ArrayList<>();
     }
 
     /**
      * Handle tab completion.
+     * <p>
+     * This will only be called if the sender is a player.
      *
      * @param sender The sender.
      * @param args   The args.
      * @return The results.
      */
     @NotNull
-    default List<String> tabComplete(@NotNull Player sender,
-                                     @NotNull List<String> args) {
+    default List<String> tabComplete(@NotNull final Player sender, @NotNull final List<String> args) {
         return new ArrayList<>();
     }
 
+    /**
+     * Throws an {@link NotificationException} relating to a specific lang.yml key.
+     * <p>
+     * This is automatically handled with eco, and should not be surrounded by a
+     * try/catch block.
+     *
+     * @param key The lang.yml key for the message to be sent.
+     * @throws NotificationException always.
+     */
+    default void notify(@NotNull final String key) throws NotificationException {
+        throw new NotificationException(key);
+    }
+
+    /**
+     * Throws an {@link NotificationException} relating to a specific lang.yml key
+     * if the passed object is null.
+     * <p>
+     * This is automatically handled with eco, and should not be surrounded by a
+     * try/catch block.
+     *
+     * @param obj The object to test.
+     * @param key The lang.yml key for the message to be sent.
+     * @param <T> The object type.
+     * @return Returns the object, definitely not-null.
+     * @throws NotificationException If the object is null.
+     */
+    @NotNull
+    default <T> T notifyNull(@Nullable final T obj,
+                             @NotNull final String key) throws NotificationException {
+        if (Objects.isNull(obj)) {
+            notify(key);
+        }
+
+        return Objects.requireNonNull(obj);
+    }
+
+    /**
+     * Throws an {@link NotificationException} relating to a specific lang.yml key
+     * if the passed object doesn't match the predicate.
+     * <p>
+     * This is automatically handled with eco, and should not be surrounded by a
+     * try/catch block.
+     *
+     * @param obj       The object to test.
+     * @param key       The lang.yml key for the message to be sent.
+     * @param predicate The predicate to test the object against.
+     * @param <T>       The type of the object.
+     * @return Returns the object, definitely not-null.
+     * @throws NotificationException If the object doesn't satisfy the predicate.
+     */
+    @NotNull
+    default <T> T notifyFalse(@NotNull final T obj,
+                              @NotNull final String key,
+                              @NotNull final Predicate<T> predicate) throws NotificationException {
+        notifyFalse(predicate.test(obj), key);
+
+        return obj;
+    }
+
+
+    /**
+     * Throws an {@link NotificationException} relating to a specific lang.yml key
+     * if a condition is false.
+     * <p>
+     * This is automatically handled with eco, and should not be surrounded by a
+     * try/catch block.
+     *
+     * @param condition The condition to test.
+     * @param key       The lang.yml key for the message to be sent.
+     * @return True.
+     * @throws NotificationException If the condition is false.
+     */
+    default boolean notifyFalse(final boolean condition,
+                                @NotNull final String key) throws NotificationException {
+        if (!condition) {
+            notify(key);
+        }
+
+        return true;
+    }
+
+    /**
+     * Throws an {@link NotificationException} relating to a specific lang.yml key
+     * if the passed string doesn't relate to a currently online player.
+     * <p>
+     * This is automatically handled with eco, and should not be surrounded by a
+     * try/catch block.
+     *
+     * @param playerName The player name.
+     * @param key        The lang.yml key for the message to be sent.
+     * @return Returns the player, definitely not-null.
+     * @throws NotificationException If the player name is invalid.
+     */
+    @NotNull
+    default Player notifyPlayerRequired(@Nullable final String playerName, @NotNull final String key) throws NotificationException {
+        if (playerName == null) {
+            notify(key);
+        }
+
+        assert playerName != null;
+
+        final Player player = Bukkit.getPlayer(playerName);
+
+        notifyNull(player, key);
+
+        return Objects.requireNonNull(player);
+    }
+
+    /**
+     * Throws an {@link NotificationException} relating to a specific lang.yml key
+     * if the passed string doesn't relate to a player on the server.
+     * <p>
+     * This is automatically handled with eco, and should not be surrounded by a
+     * try/catch block.
+     *
+     * @param playerName The player name.
+     * @param key        The lang.yml key for the message to be sent.
+     * @return Returns the offline player, definitely not-null.
+     * @throws NotificationException If the player name is invalid.
+     */
+    @NotNull
+    default OfflinePlayer notifyOfflinePlayerRequired(@Nullable final String playerName,
+                                                      @NotNull final String key) throws NotificationException {
+        if (playerName == null) {
+            notify(key);
+        }
+
+        assert playerName != null;
+
+        @SuppressWarnings("deprecation") final OfflinePlayer player = Bukkit.getOfflinePlayer(playerName);
+
+        boolean hasPlayedBefore = player.hasPlayedBefore() || player.isOnline();
+
+        notifyFalse(!hasPlayedBefore, key);
+
+        return player;
+    }
+
+    /**
+     * Throws an exception containing a langYml key if player doesn't have permission.
+     *
+     * @param player     The player.
+     * @param permission The permission.
+     * @param key        The lang.yml key for the message to be sent.
+     * @return The player.
+     * @throws NotificationException If the player doesn't have the required permission.
+     */
+    @NotNull
+    default Player notifyPermissionRequired(@NotNull final Player player,
+                                            @NotNull final String permission,
+                                            @NotNull final String key) throws NotificationException {
+        return notifyFalse(player, key, p -> p.hasPermission(permission));
+    }
+
     /**
      * Get the plugin.
      *
      * @return The plugin.
      */
     EcoPlugin getPlugin();
-
-    /**
-     * Get the handler.
-     *
-     * @return The handler.
-     * @see CommandHandler
-     * @deprecated Use {@link CommandBase#onExecute(CommandSender, List)} instead.
-     */
-    @Deprecated(forRemoval = true)
-    default CommandHandler getHandler() {
-        return (a, b) -> {
-
-        };
-    }
-
-    /**
-     * Set the handler.
-     *
-     * @param handler The handler.
-     * @see CommandHandler
-     * @deprecated Handlers have been deprecated.
-     */
-    @Deprecated(forRemoval = true)
-    default void setHandler(@NotNull final CommandHandler handler) {
-        // Do nothing.
-    }
-
-    /**
-     * Get the tab completer.
-     *
-     * @return The tab completer.
-     * @see TabCompleteHandler
-     * @deprecated Use {@link CommandBase#tabComplete(CommandSender, List)} instead.
-     */
-    @Deprecated(forRemoval = true)
-    default TabCompleteHandler getTabCompleter() {
-        return (a, b) -> ImmutableList.of();
-    }
-
-    /**
-     * Set the tab completer.
-     *
-     * @param handler The handler.
-     * @see TabCompleteHandler
-     * @deprecated Handlers have been deprecated.
-     */
-    @Deprecated(forRemoval = true)
-    default void setTabCompleter(@NotNull final TabCompleteHandler handler) {
-        // Do nothing.
-    }
 }

eco-api/src/main/java/com/willfp/eco/core/command/CommandHandler.java

@@ -1,29 +0,0 @@
-package com.willfp.eco.core.command;
-
-import org.bukkit.command.Command;
-import org.bukkit.command.CommandSender;
-import org.jetbrains.annotations.NotNull;
-
-import java.util.List;
-
-/**
- * A command handler handles the actual code for a command.
- * <p>
- * The replacement for {@link org.bukkit.command.CommandExecutor#onCommand(CommandSender, Command, String, String[])}
- *
- * @see CommandBase
- * @deprecated Handlers have been deprecated. This legacy system will eventually be removed,
- * update to use the new system: {@link CommandBase#onExecute(CommandSender, List)}.
- */
-@FunctionalInterface
-@Deprecated(since = "6.17.0", forRemoval = true)
-public interface CommandHandler {
-    /**
-     * The code to be called on execution.
-     *
-     * @param sender The sender.
-     * @param args   The arguments.
-     */
-    void onExecute(@NotNull CommandSender sender,
-                   @NotNull List<String> args);
-}

eco-api/src/main/java/com/willfp/eco/core/command/NotificationException.java

@@ -0,0 +1,36 @@
+package com.willfp.eco.core.command;
+
+import org.jetbrains.annotations.NotNull;
+
+/**
+ * A notification exception is thrown when {@link org.bukkit.command.CommandSender}s don't
+ * specify valid arguments in commands.
+ * <p>
+ * Methods in eco that throw this will contain automatic handling and thus
+ * should not be surrounded by try / catch blocks.
+ */
+public class NotificationException extends Exception {
+    /**
+     * The key for the lang.yml message to be sent.
+     */
+    private final String key;
+
+    /**
+     * Creates a notification exception.
+     *
+     * @param key The lang key of the notification.
+     */
+    public NotificationException(@NotNull final String key) {
+        super(key);
+        this.key = key;
+    }
+
+    /**
+     * Get the lang key.
+     *
+     * @return The lang key.
+     */
+    public String getKey() {
+        return key;
+    }
+}

eco-api/src/main/java/com/willfp/eco/core/command/PluginCommandBase.java

@@ -0,0 +1,44 @@
+package com.willfp.eco.core.command;
+
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Plugin command bases can be registered directly with the server,
+ * this essentially functions as the interface that is implemented generically
+ * via {@link com.willfp.eco.core.command.impl.PluginCommand}.
+ */
+public interface PluginCommandBase extends CommandBase {
+    /**
+     * Register the PluginCommandBase to the bukkit commandMap.
+     */
+    void register();
+
+    /**
+     * Unregister the PluginCommandBase from the bukkit commandMap.
+     */
+    void unregister();
+
+    /**
+     * Get aliases. Leave null if this command is from plugin.yml.
+     *
+     * @return The aliases.
+     */
+    @NotNull
+    default List<String> getAliases() {
+        return new ArrayList<>();
+    }
+
+    /**
+     * Get description.
+     *
+     * @return The description.
+     */
+    @Nullable
+    default String getDescription() {
+        return null;
+    }
+}

eco-api/src/main/java/com/willfp/eco/core/command/TabCompleteHandler.java

@@ -1,30 +0,0 @@
-package com.willfp.eco.core.command;
-
-import org.bukkit.command.Command;
-import org.bukkit.command.CommandSender;
-import org.jetbrains.annotations.NotNull;
-
-import java.util.List;
-
-/**
- * A Tab Complete handler handles the actual tab-completion code.
- * <p>
- * The replacement for {@link org.bukkit.command.TabCompleter#onTabComplete(CommandSender, Command, String, String[])}
- *
- * @see CommandBase
- * @deprecated Handlers have been deprecated. This legacy system will eventually be removed,
- * update to use the new system: {@link CommandBase#tabComplete(CommandSender, List)}
- */
-@FunctionalInterface
-@Deprecated(since = "6.17.0", forRemoval = true)
-public interface TabCompleteHandler {
-    /**
-     * Handle Tab Completion.
-     *
-     * @param sender The sender.
-     * @param args   The arguments.
-     * @return The tab completion results.
-     */
-    List<String> tabComplete(@NotNull CommandSender sender,
-                             @NotNull List<String> args);
-}

eco-api/src/main/java/com/willfp/eco/core/command/impl/DelegatedBukkitCommand.java

@@ -6,13 +6,15 @@ import org.bukkit.command.PluginIdentifiableCommand;
 import org.bukkit.command.TabCompleter;
 import org.bukkit.plugin.Plugin;
 import org.jetbrains.annotations.NotNull;
-import org.jetbrains.annotations.Nullable;
 
 import java.util.List;
 
 /**
  * Delegates a bukkit command to an eco command (for registrations).
+ *
+ * @deprecated Internal command implementations have been removed from the API.
  */
+@Deprecated(forRemoval = true, since = "6.49.0")
 public final class DelegatedBukkitCommand extends Command implements TabCompleter, PluginIdentifiableCommand {
     /**
      * The delegate command.
@@ -34,7 +36,7 @@ public final class DelegatedBukkitCommand extends Command implements TabComplete
     public boolean execute(@NotNull final CommandSender commandSender,
                            @NotNull final String label,
                            @NotNull final String[] args) {
-        return delegate.onCommand(commandSender, this, label, args);
+        return false;
     }
 
     @Override
@@ -42,7 +44,7 @@ public final class DelegatedBukkitCommand extends Command implements TabComplete
                                       @NotNull final Command command,
                                       @NotNull final String label,
                                       @NotNull final String[] args) {
-        return delegate.onTabComplete(commandSender, command, label, args);
+        return List.of();
     }
 
     @NotNull
@@ -51,9 +53,8 @@ public final class DelegatedBukkitCommand extends Command implements TabComplete
         return this.delegate.getPlugin();
     }
 
-    @Nullable
     @Override
-    public String getPermission() {
+    public @NotNull String getPermission() {
         return this.delegate.getPermission();
     }
 

eco-api/src/main/java/com/willfp/eco/core/command/impl/HandledCommand.java

@@ -1,294 +0,0 @@
-package com.willfp.eco.core.command.impl;
-
-import com.willfp.eco.core.EcoPlugin;
-import com.willfp.eco.core.command.CommandBase;
-import org.bukkit.command.CommandSender;
-import org.bukkit.entity.Player;
-import org.bukkit.util.StringUtil;
-import org.jetbrains.annotations.NotNull;
-import org.jetbrains.annotations.Nullable;
-
-import java.util.ArrayList;
-import java.util.Arrays;
-import java.util.Collections;
-import java.util.List;
-import java.util.stream.Collectors;
-
-/**
- * Abstract class for commands that can be handled.
- * <p>
- * Handled commands have a method to pass in raw input from bukkit commands
- * in order to execute the command-specific code. It's essentially an internal
- * layer, hence why it's a package-private class.
- */
-@SuppressWarnings({"DeprecatedIsStillUsed", "removal"})
-abstract class HandledCommand implements CommandBase {
-    /**
-     * The plugin.
-     */
-    private final EcoPlugin plugin;
-
-    /**
-     * The name of the command.
-     */
-    private final String name;
-
-    /**
-     * The permission required to execute the command.
-     * <p>
-     * Written out as a string for flexibility with subclasses.
-     */
-    private final String permission;
-
-    /**
-     * Should the command only be allowed to be executed by players?
-     * <p>
-     * In other worlds, only allowed to be executed by console.
-     */
-    private final boolean playersOnly;
-
-    /**
-     * The actual code to be executed in the command.
-     */
-    @Deprecated
-    @Nullable
-    private com.willfp.eco.core.command.CommandHandler handler = null;
-
-    /**
-     * The tab completion code to be executed in the command.
-     */
-    @Deprecated
-    @Nullable
-    private com.willfp.eco.core.command.TabCompleteHandler tabCompleter = null;
-
-    /**
-     * All subcommands for the command.
-     */
-    private final List<CommandBase> subcommands;
-
-    /**
-     * Create a new command.
-     * <p>
-     * The name cannot be the same as an existing command as this will conflict.
-     *
-     * @param plugin      Instance of a plugin.
-     * @param name        The name used in execution.
-     * @param permission  The permission required to execute the command.
-     * @param playersOnly If only players should be able to execute this command.
-     */
-    HandledCommand(@NotNull final EcoPlugin plugin,
-                   @NotNull final String name,
-                   @NotNull final String permission,
-                   final boolean playersOnly) {
-        this.plugin = plugin;
-        this.name = name;
-        this.permission = permission;
-        this.playersOnly = playersOnly;
-        this.subcommands = new ArrayList<>();
-    }
-
-    /**
-     * Add a subcommand to the command.
-     *
-     * @param subcommand The subcommand.
-     * @return The parent command.
-     */
-    @Override
-    public final CommandBase addSubcommand(@NotNull final CommandBase subcommand) {
-        subcommands.add(subcommand);
-
-        return this;
-    }
-
-    /**
-     * Get the plugin.
-     *
-     * @return The plugin.
-     */
-    @Override
-    public EcoPlugin getPlugin() {
-        return this.plugin;
-    }
-
-    /**
-     * Handle the command.
-     *
-     * @param sender The sender.
-     * @param args   The arguments.
-     */
-    protected final void handle(@NotNull final CommandSender sender,
-                                @NotNull final String[] args) {
-        if (!canExecute(sender, this, this.getPlugin())) {
-            return;
-        }
-
-        if (args.length > 0) {
-            for (CommandBase subcommand : this.getSubcommands()) {
-                if (subcommand.getName().equalsIgnoreCase(args[0])) {
-                    if (!canExecute(sender, subcommand, this.getPlugin())) {
-                        return;
-                    }
-
-                    ((HandledCommand) subcommand).handle(sender, Arrays.copyOfRange(args, 1, args.length));
-
-                    return;
-                }
-            }
-        }
-
-        if (this.isPlayersOnly() && !(sender instanceof Player)) {
-            sender.sendMessage(this.getPlugin().getLangYml().getMessage("not-player"));
-            return;
-        }
-
-        if (this.getHandler() != null) {
-            this.getHandler().onExecute(sender, Arrays.asList(args));
-        } else {
-            this.onExecute(sender, Arrays.asList(args));
-            if (sender instanceof Player player) {
-                this.onExecute(player, Arrays.asList(args));
-            }
-        }
-    }
-
-    /**
-     * Handle the tab completion.
-     *
-     * @param sender The sender.
-     * @param args   The arguments.
-     * @return The tab completion results.
-     */
-    protected final List<String> handleTabCompletion(@NotNull final CommandSender sender,
-                                                     @NotNull final String[] args) {
-
-        if (!sender.hasPermission(this.getPermission())) {
-            return null;
-        }
-
-        if (args.length == 1) {
-            List<String> completions = new ArrayList<>();
-
-            StringUtil.copyPartialMatches(
-                    args[0],
-                    this.getSubcommands().stream()
-                            .filter(subCommand -> sender.hasPermission(subCommand.getPermission()))
-                            .map(CommandBase::getName)
-                            .collect(Collectors.toList()),
-                    completions
-            );
-
-            Collections.sort(completions);
-
-            if (!completions.isEmpty()) {
-                return completions;
-            }
-        }
-
-        if (args.length >= 2) {
-            HandledCommand command = null;
-
-            for (CommandBase subcommand : this.getSubcommands()) {
-                if (!sender.hasPermission(subcommand.getPermission())) {
-                    continue;
-                }
-
-                if (args[0].equalsIgnoreCase(subcommand.getName())) {
-                    command = (HandledCommand) subcommand;
-                }
-            }
-
-            if (command != null) {
-                return command.handleTabCompletion(sender, Arrays.copyOfRange(args, 1, args.length));
-            }
-        }
-
-        if (this.getTabCompleter() != null) {
-            return this.getTabCompleter().tabComplete(sender, Arrays.asList(args));
-        } else {
-            List<String> completions = new ArrayList<>(this.tabComplete(sender, Arrays.asList(args)));
-            if (sender instanceof Player player) {
-                completions.addAll(this.tabComplete(player, Arrays.asList(args)));
-            }
-            return completions;
-        }
-    }
-
-    /**
-     * If a sender can execute the command.
-     *
-     * @param sender  The sender.
-     * @param command The command.
-     * @param plugin  The plugin.
-     * @return If the sender can execute.
-     */
-    public static boolean canExecute(@NotNull final CommandSender sender,
-                                     @NotNull final CommandBase command,
-                                     @NotNull final EcoPlugin plugin) {
-        if (!sender.hasPermission(command.getPermission()) && sender instanceof Player) {
-            sender.sendMessage(plugin.getLangYml().getNoPermission());
-            return false;
-        }
-
-        return true;
-    }
-
-    /**
-     * Get the command name.
-     *
-     * @return The name.
-     */
-    public String getName() {
-        return this.name;
-    }
-
-    /**
-     * Get the permission required to execute the command.
-     *
-     * @return The permission.
-     */
-    public String getPermission() {
-        return this.permission;
-    }
-
-    /**
-     * Get if the command can only be executed by players.
-     *
-     * @return If players only.
-     */
-    public boolean isPlayersOnly() {
-        return this.playersOnly;
-    }
-
-    /**
-     * Get the subcommands of the command.
-     *
-     * @return The subcommands.
-     */
-    public List<CommandBase> getSubcommands() {
-        return this.subcommands;
-    }
-
-    @Deprecated(forRemoval = true)
-    @Override
-    public @Nullable com.willfp.eco.core.command.CommandHandler getHandler() {
-        return this.handler;
-    }
-
-    @Deprecated(forRemoval = true)
-    @Override
-    public @Nullable com.willfp.eco.core.command.TabCompleteHandler getTabCompleter() {
-        return this.tabCompleter;
-    }
-
-    @Deprecated(forRemoval = true)
-    @Override
-    public void setHandler(@Nullable final com.willfp.eco.core.command.CommandHandler handler) {
-        this.handler = handler;
-    }
-
-    @Deprecated(forRemoval = true)
-    @Override
-    public void setTabCompleter(@Nullable final com.willfp.eco.core.command.TabCompleteHandler tabCompleter) {
-        this.tabCompleter = tabCompleter;
-    }
-}

eco-api/src/main/java/com/willfp/eco/core/command/impl/PluginCommand.java

@@ -2,29 +2,27 @@ package com.willfp.eco.core.command.impl;
 
 import com.willfp.eco.core.Eco;
 import com.willfp.eco.core.EcoPlugin;
-import org.bukkit.Bukkit;
-import org.bukkit.command.Command;
-import org.bukkit.command.CommandExecutor;
-import org.bukkit.command.CommandMap;
-import org.bukkit.command.CommandSender;
-import org.bukkit.command.TabCompleter;
+import com.willfp.eco.core.command.CommandBase;
+import com.willfp.eco.core.command.PluginCommandBase;
 import org.jetbrains.annotations.NotNull;
-import org.jetbrains.annotations.Nullable;
 
-import java.lang.reflect.Field;
-import java.util.ArrayList;
 import java.util.List;
 
 /**
- * PluginCommands are the class to be used instead of CommandExecutor,
- * they function as the base command, e.g. {@code /ecoenchants} would be a base command, with each
- * subsequent argument functioning as subcommands.
+ * PluginCommands are the class to be used instead of CommandExecutor, they function as the base
+ * command, e.g. {@code /ecoenchants} would be a base command, with each subsequent argument
+ * functioning as subcommands.
  * <p>
  * The command will not be registered until register() is called.
  * <p>
  * The name cannot be the same as an existing command as this will conflict.
  */
-public abstract class PluginCommand extends HandledCommand implements CommandExecutor, TabCompleter {
+public abstract class PluginCommand implements PluginCommandBase {
+    /**
+     * The delegate command.
+     */
+    private final PluginCommandBase delegate;
+
     /**
      * Create a new command.
      *
@@ -37,128 +35,51 @@ public abstract class PluginCommand extends HandledCommand implements CommandExe
                             @NotNull final String name,
                             @NotNull final String permission,
                             final boolean playersOnly) {
-        super(plugin, name, permission, playersOnly);
+        this.delegate = Eco.get().createPluginCommand(this, plugin, name, permission, playersOnly);
     }
 
-    /**
-     * Registers the command with the server,
-     */
-    public final void register() {
-        org.bukkit.command.PluginCommand command = Bukkit.getPluginCommand(this.getName());
-        if (command != null) {
-            command.setExecutor(this);
-            command.setTabCompleter(this);
-
-            if (this.getDescription() != null) {
-                command.setDescription(this.getDescription());
-            }
-
-            List<String> aliases = new ArrayList<>(command.getAliases());
-            aliases.addAll(this.getAliases());
-            command.setAliases(aliases);
-        } else {
-            this.unregister();
-
-            CommandMap commandMap = getCommandMap();
-
-            commandMap.register(this.getPlugin().getName().toLowerCase(), new DelegatedBukkitCommand(this));
-        }
-
-        Eco.get().syncCommands();
-    }
-
-    /**
-     * Unregisters the command from the server.
-     */
-    public final void unregister() {
-        CommandMap commandMap = getCommandMap();
-
-        Command found = commandMap.getCommand(this.getName());
-        if (found != null) {
-            found.unregister(commandMap);
-        }
-
-        Eco.get().syncCommands();
-    }
-
-    /**
-     * Get aliases. Leave null if this command is from plugin.yml.
-     *
-     * @return The aliases.
-     */
-    @NotNull
-    public List<String> getAliases() {
-        return new ArrayList<>();
-    }
-
-    /**
-     * Get description.
-     *
-     * @return The description.
-     */
-    @Nullable
-    public String getDescription() {
-        return null;
-    }
-
-    /**
-     * Internal implementation used to clean up boilerplate.
-     * Used for parity with {@link CommandExecutor#onCommand(CommandSender, Command, String, String[])}.
-     *
-     * @param sender  The executor of the command.
-     * @param command The bukkit command.
-     * @param label   The name of the executed command.
-     * @param args    The arguments of the command (anything after the physical command name)
-     * @return If the command was processed by the linked {@link EcoPlugin}
-     */
     @Override
-    public final boolean onCommand(@NotNull final CommandSender sender,
-                                   @NotNull final Command command,
-                                   @NotNull final String label,
-                                   @NotNull final String[] args) {
-        if (!command.getName().equalsIgnoreCase(this.getName())) {
-            return false;
+    public @NotNull String getName() {
+        return delegate.getName();
     }
 
-        this.handle(sender, args);
-
-        return true;
-    }
-
-    /**
-     * Internal implementation used to clean up boilerplate.
-     * Used for parity with {@link TabCompleter#onTabComplete(CommandSender, Command, String, String[])}.
-     *
-     * @param sender  The executor of the command.
-     * @param command The bukkit command.
-     * @param label   The name of the executed command.
-     * @param args    The arguments of the command (anything after the physical command name).
-     * @return The list of tab-completions.
-     */
     @Override
-    public @Nullable List<String> onTabComplete(@NotNull final CommandSender sender,
-                                                @NotNull final Command command,
-                                                @NotNull final String label,
-                                                @NotNull final String[] args) {
-        if (!command.getName().equalsIgnoreCase(this.getName())) {
-            return null;
+    public @NotNull String getPermission() {
+        return delegate.getPermission();
     }
 
-        return this.handleTabCompletion(sender, args);
+    @Override
+    public boolean isPlayersOnly() {
+        return delegate.isPlayersOnly();
     }
 
-    /**
-     * Get the internal server CommandMap.
-     *
-     * @return The CommandMap.
-     */
-    public static CommandMap getCommandMap() {
-        try {
-            Field field = Bukkit.getServer().getClass().getDeclaredField("commandMap");
-            field.setAccessible(true);
-            return (CommandMap) field.get(Bukkit.getServer());
-        } catch (NoSuchFieldException | IllegalAccessException e) {
-            throw new NullPointerException("Command map wasn't found!");
-        }
+    @Override
+    public @NotNull CommandBase addSubcommand(@NotNull CommandBase command) {
+        return delegate.addSubcommand(command);
+    }
+
+    @Override
+    public @NotNull List<CommandBase> getSubcommands() {
+        return delegate.getSubcommands();
+    }
+
+    @Override
+    public @NotNull CommandBase getWrapped() {
+        return this;
+    }
+
+    @Override
+    public void register() {
+        delegate.register();
+    }
+
+    @Override
+    public void unregister() {
+        delegate.unregister();
+    }
+
+    @Override
+    public EcoPlugin getPlugin() {
+        return delegate.getPlugin();
     }
 }

eco-api/src/main/java/com/willfp/eco/core/command/impl/Subcommand.java

@@ -1,13 +1,21 @@
 package com.willfp.eco.core.command.impl;
 
+import com.willfp.eco.core.Eco;
 import com.willfp.eco.core.EcoPlugin;
 import com.willfp.eco.core.command.CommandBase;
 import org.jetbrains.annotations.NotNull;
 
+import java.util.List;
+
 /**
- * Subcommands can be added to PluginCommands or to other Subcommands.
+ * A command implementation that must exist as a subcommand (i.e. cannot be registered directly).
  */
-public abstract class Subcommand extends HandledCommand {
+public abstract class Subcommand implements CommandBase {
+    /**
+     * The delegate command.
+     */
+    private final CommandBase delegate;
+
     /**
      * Create subcommand.
      *
@@ -20,7 +28,7 @@ public abstract class Subcommand extends HandledCommand {
                          @NotNull final String name,
                          @NotNull final String permission,
                          final boolean playersOnly) {
-        super(plugin, name, permission, playersOnly);
+        this.delegate = Eco.get().createSubcommand(this, plugin, name, permission, playersOnly);
     }
 
     /**
@@ -33,6 +41,41 @@ public abstract class Subcommand extends HandledCommand {
     protected Subcommand(@NotNull final EcoPlugin plugin,
                          @NotNull final String name,
                          @NotNull final CommandBase parent) {
-        super(plugin, name, parent.getPermission(), parent.isPlayersOnly());
+        this(plugin, name, parent.getPermission(), parent.isPlayersOnly());
+    }
+
+    @Override
+    public @NotNull String getName() {
+        return delegate.getName();
+    }
+
+    @Override
+    public @NotNull String getPermission() {
+        return delegate.getPermission();
+    }
+
+    @Override
+    public boolean isPlayersOnly() {
+        return delegate.isPlayersOnly();
+    }
+
+    @Override
+    public @NotNull CommandBase addSubcommand(@NotNull CommandBase command) {
+        return delegate.addSubcommand(command);
+    }
+
+    @Override
+    public @NotNull List<CommandBase> getSubcommands() {
+        return delegate.getSubcommands();
+    }
+
+    @Override
+    public @NotNull CommandBase getWrapped() {
+        return this;
+    }
+
+    @Override
+    public EcoPlugin getPlugin() {
+        return delegate.getPlugin();
     }
 }

eco-api/src/main/java/com/willfp/eco/core/config/base/LangYml.java

@@ -6,10 +6,32 @@ import com.willfp.eco.core.config.ConfigType;
 import com.willfp.eco.util.StringUtils;
 import org.jetbrains.annotations.NotNull;
 
+import java.util.List;
+
 /**
  * Default plugin lang.yml.
  */
 public class LangYml extends BaseConfig {
+    /**
+     * The messages key.
+     */
+    public static final String KEY_MESSAGES = "messages";
+
+    /**
+     * The prefix key.
+     */
+    public static final String KEY_PREFIX = "messages.prefix";
+
+    /**
+     * The no permission key.
+     */
+    public static final String KEY_NO_PERMISSION = "messages.no-permission";
+
+    /**
+     * The not player key.
+     */
+    public static final String KEY_NOT_PLAYER = "messages.not-player";
+
     /**
      * Lang.yml.
      *
@@ -19,13 +41,31 @@ public class LangYml extends BaseConfig {
         super("lang", plugin, false, ConfigType.YAML);
     }
 
+    /**
+     * lang.yml requires certain keys to be present.
+     * <p>
+     * If the lang.yml does not contain these keys, it is considered to be
+     * invalid and thus will show a warning in console.
+     *
+     * @return If valid.
+     */
+    public boolean isValid() {
+        for (String key : List.of(KEY_MESSAGES, KEY_PREFIX, KEY_NO_PERMISSION, KEY_NOT_PLAYER)) {
+            if (!this.has(key)) {
+                return false;
+            }
+        }
+
+        return true;
+    }
+
     /**
      * Get the prefix for messages in chat.
      *
      * @return The prefix.
      */
     public String getPrefix() {
-        return this.getFormattedString("messages.prefix");
+        return this.getFormattedString(KEY_PREFIX);
     }
 
     /**
@@ -34,7 +74,7 @@ public class LangYml extends BaseConfig {
      * @return The message.
      */
     public String getNoPermission() {
-        return getPrefix() + this.getFormattedString("messages.no-permission");
+        return getPrefix() + this.getFormattedString(KEY_NO_PERMISSION);
     }
 
     /**
@@ -56,6 +96,6 @@ public class LangYml extends BaseConfig {
      */
     public String getMessage(@NotNull final String message,
                              @NotNull final StringUtils.FormatOption option) {
-        return getPrefix() + this.getFormattedString("messages." + message, option);
+        return getPrefix() + this.getFormattedString(KEY_MESSAGES + "." + message, option);
     }
 }

eco-api/src/main/java/com/willfp/eco/core/data/keys/PersistentDataKey.java

@@ -134,7 +134,7 @@ public final class PersistentDataKey<T> {
         if (this == o) {
             return true;
         }
-        if (!(o instanceof PersistentDataKey that)) {
+        if (!(o instanceof PersistentDataKey<?> that)) {
             return false;
         }
         return Objects.equals(this.getKey(), that.getKey());

eco-api/src/main/java/com/willfp/eco/core/data/keys/PersistentDataKeyType.java

@@ -99,7 +99,7 @@ public final class PersistentDataKeyType<T> {
         if (this == that) {
             return true;
         }
-        if (!(that instanceof PersistentDataKeyType type)) {
+        if (!(that instanceof PersistentDataKeyType<?> type)) {
             return false;
         }
         return Objects.equals(this.name, type.name);

eco-api/src/main/java/com/willfp/eco/core/display/Display.java

@@ -1,6 +1,7 @@
 package com.willfp.eco.core.display;
 
 import com.willfp.eco.core.fast.FastItemStack;
+import com.willfp.eco.core.integrations.guidetection.GUIDetectionManager;
 import com.willfp.eco.util.NamespacedKeyUtils;
 import org.bukkit.NamespacedKey;
 import org.bukkit.entity.Player;
@@ -18,6 +19,9 @@ import java.util.TreeMap;
 
 /**
  * Utility class to manage client-side item display.
+ * <p>
+ * Packet display is not done on the main thread, so make sure
+ * all your modules are thread-safe.
  */
 public final class Display {
     /**
@@ -71,7 +75,7 @@ public final class Display {
         ItemStack original = itemStack.clone();
         Inventory inventory = player == null ? null : player.getOpenInventory().getTopInventory();
         boolean inInventory = inventory != null && inventory.contains(original);
-        boolean inGui = inventory != null && inventory.getHolder() == null;
+        boolean inGui = player != null && GUIDetectionManager.hasGUIOpen(player);
 
         DisplayProperties properties = new DisplayProperties(
                 inInventory,

eco-api/src/main/java/com/willfp/eco/core/display/DisplayModule.java

@@ -8,6 +8,8 @@ import org.jetbrains.annotations.Nullable;
 
 /**
  * Class for all plugin-specific client-side item display modules.
+ * <p>
+ * Display modules are called in the netty thread, so make sure they are thread-safe.
  */
 public abstract class DisplayModule {
     /**

eco-api/src/main/java/com/willfp/eco/core/entities/ai/entity/EntityGoalAvoidEntity.java

@@ -45,7 +45,6 @@ public record EntityGoalAvoidEntity(
                 return null;
             }
 
-            try {
             TestableEntity entity = Entities.lookup(config.getString("entity"));
 
             return new EntityGoalAvoidEntity(
@@ -54,14 +53,6 @@ public record EntityGoalAvoidEntity(
                     config.getDouble("slowSpeed"),
                     config.getDouble("fastSpeed")
             );
-            } catch (Exception e) {
-                /*
-                Exceptions could be caused by configs having values of a wrong type,
-                invalid enum parameters, etc. Serializers shouldn't throw exceptions,
-                so we encapsulate them as null.
-                 */
-                return null;
-            }
         }
 
         @NotNull

eco-api/src/main/java/com/willfp/eco/core/entities/ai/entity/EntityGoalBreakDoors.java

@@ -34,18 +34,9 @@ public record EntityGoalBreakDoors(
                 return null;
             }
 
-            try {
             return new EntityGoalBreakDoors(
                     config.getInt("ticks")
             );
-            } catch (Exception e) {
-                /*
-                Exceptions could be caused by configs having values of a wrong type,
-                invalid enum parameters, etc. Serializers shouldn't throw exceptions,
-                so we encapsulate them as null.
-                 */
-                return null;
-            }
         }
 
         @NotNull

eco-api/src/main/java/com/willfp/eco/core/entities/ai/entity/EntityGoalBreed.java

@@ -34,18 +34,9 @@ public record EntityGoalBreed(
                 return null;
             }
 
-            try {
             return new EntityGoalBreed(
                     config.getDouble("speed")
             );
-            } catch (Exception e) {
-                /*
-                Exceptions could be caused by configs having values of a wrong type,
-                invalid enum parameters, etc. Serializers shouldn't throw exceptions,
-                so we encapsulate them as null.
-                 */
-                return null;
-            }
         }
 
         @NotNull

eco-api/src/main/java/com/willfp/eco/core/entities/ai/entity/EntityGoalCatLieOnBed.java

@@ -37,19 +37,10 @@ public record EntityGoalCatLieOnBed(
                 return null;
             }
 
-            try {
             return new EntityGoalCatLieOnBed(
                     config.getDouble("speed"),
                     config.getInt("range")
             );
-            } catch (Exception e) {
-                /*
-                Exceptions could be caused by configs having values of a wrong type,
-                invalid enum parameters, etc. Serializers shouldn't throw exceptions,
-                so we encapsulate them as null.
-                 */
-                return null;
-            }
         }
 
         @NotNull

eco-api/src/main/java/com/willfp/eco/core/entities/ai/entity/EntityGoalCatSitOnBed.java

@@ -34,18 +34,9 @@ public record EntityGoalCatSitOnBed(
                 return null;
             }
 
-            try {
             return new EntityGoalCatSitOnBed(
                     config.getDouble("speed")
             );
-            } catch (Exception e) {
-                /*
-                Exceptions could be caused by configs having values of a wrong type,
-                invalid enum parameters, etc. Serializers shouldn't throw exceptions,
-                so we encapsulate them as null.
-                 */
-                return null;
-            }
         }
 
         @NotNull

eco-api/src/main/java/com/willfp/eco/core/entities/ai/entity/EntityGoalFleeSun.java

@@ -34,18 +34,9 @@ public record EntityGoalFleeSun(
                 return null;
             }
 
-            try {
             return new EntityGoalFleeSun(
                     config.getDouble("speed")
             );
-            } catch (Exception e) {
-                /*
-                Exceptions could be caused by configs having values of a wrong type,
-                invalid enum parameters, etc. Serializers shouldn't throw exceptions,
-                so we encapsulate them as null.
-                 */
-                return null;
-            }
         }
 
         @NotNull

eco-api/src/main/java/com/willfp/eco/core/entities/ai/entity/EntityGoalFollowMobs.java

@@ -40,20 +40,11 @@ public record EntityGoalFollowMobs(
                 return null;
             }
 
-            try {
             return new EntityGoalFollowMobs(
                     config.getDouble("speed"),
                     config.getDouble("minDistance"),
                     config.getDouble("maxDistance")
             );
-            } catch (Exception e) {
-                /*
-                Exceptions could be caused by configs having values of a wrong type,
-                invalid enum parameters, etc. Serializers shouldn't throw exceptions,
-                so we encapsulate them as null.
-                 */
-                return null;
-            }
         }
 
         @NotNull

eco-api/src/main/java/com/willfp/eco/core/entities/ai/entity/EntityGoalInteract.java

@@ -42,20 +42,11 @@ public record EntityGoalInteract(
                 return null;
             }
 
-            try {
             return new EntityGoalInteract(
                     Entities.lookup(config.getString("target")),
                     config.getDouble("range"),
                     config.getDouble("chance")
             );
-            } catch (Exception e) {
-                /*
-                Exceptions could be caused by configs having values of a wrong type,
-                invalid enum parameters, etc. Serializers shouldn't throw exceptions,
-                so we encapsulate them as null.
-                 */
-                return null;
-            }
         }
 
         @NotNull

eco-api/src/main/java/com/willfp/eco/core/entities/ai/entity/EntityGoalLeapAtTarget.java

@@ -34,18 +34,9 @@ public record EntityGoalLeapAtTarget(
                 return null;
             }
 
-            try {
             return new EntityGoalLeapAtTarget(
                     config.getDouble("velocity")
             );
-            } catch (Exception e) {
-                /*
-                Exceptions could be caused by configs having values of a wrong type,
-                invalid enum parameters, etc. Serializers shouldn't throw exceptions,
-                so we encapsulate them as null.
-                 */
-                return null;
-            }
         }
 
         @NotNull

eco-api/src/main/java/com/willfp/eco/core/entities/ai/entity/EntityGoalLookAtPlayer.java

@@ -37,19 +37,10 @@ public record EntityGoalLookAtPlayer(
                 return null;
             }
 
-            try {
             return new EntityGoalLookAtPlayer(
                     config.getDouble("range"),
                     config.getDouble("chance")
             );
-            } catch (Exception e) {
-                /*
-                Exceptions could be caused by configs having values of a wrong type,
-                invalid enum parameters, etc. Serializers shouldn't throw exceptions,
-                so we encapsulate them as null.
-                 */
-                return null;
-            }
         }
 
         @NotNull

eco-api/src/main/java/com/willfp/eco/core/entities/ai/entity/EntityGoalMeleeAttack.java

@@ -37,19 +37,10 @@ public record EntityGoalMeleeAttack(
                 return null;
             }
 
-            try {
             return new EntityGoalMeleeAttack(
                     config.getDouble("speed"),
                     config.getBool("pauseWhenMobIdle")
             );
-            } catch (Exception e) {
-                /*
-                Exceptions could be caused by configs having values of a wrong type,
-                invalid enum parameters, etc. Serializers shouldn't throw exceptions,
-                so we encapsulate them as null.
-                 */
-                return null;
-            }
         }
 
         @NotNull

eco-api/src/main/java/com/willfp/eco/core/entities/ai/entity/EntityGoalMoveBackToVillage.java

@@ -37,19 +37,10 @@ public record EntityGoalMoveBackToVillage(
                 return null;
             }
 
-            try {
             return new EntityGoalMoveBackToVillage(
                     config.getDouble("speed"),
                     config.getBool("canDespawn")
             );
-            } catch (Exception e) {
-                /*
-                Exceptions could be caused by configs having values of a wrong type,
-                invalid enum parameters, etc. Serializers shouldn't throw exceptions,
-                so we encapsulate them as null.
-                 */
-                return null;
-            }
         }
 
         @NotNull

eco-api/src/main/java/com/willfp/eco/core/entities/ai/entity/EntityGoalMoveThroughVillage.java

@@ -43,21 +43,12 @@ public record EntityGoalMoveThroughVillage(
                 return null;
             }
 
-            try {
             return new EntityGoalMoveThroughVillage(
                     config.getDouble("speed"),
                     config.getBool("onlyAtNight"),
                     config.getInt("distance"),
                     config.getBool("canPassThroughDoors")
             );
-            } catch (Exception e) {
-                /*
-                Exceptions could be caused by configs having values of a wrong type,
-                invalid enum parameters, etc. Serializers shouldn't throw exceptions,
-                so we encapsulate them as null.
-                 */
-                return null;
-            }
         }
 
         @NotNull

eco-api/src/main/java/com/willfp/eco/core/entities/ai/entity/EntityGoalMoveTowardsRestriction.java

@@ -34,18 +34,9 @@ public record EntityGoalMoveTowardsRestriction(
                 return null;
             }
 
-            try {
             return new EntityGoalMoveTowardsRestriction(
                     config.getDouble("speed")
             );
-            } catch (Exception e) {
-                /*
-                Exceptions could be caused by configs having values of a wrong type,
-                invalid enum parameters, etc. Serializers shouldn't throw exceptions,
-                so we encapsulate them as null.
-                 */
-                return null;
-            }
         }
 
         @NotNull

eco-api/src/main/java/com/willfp/eco/core/entities/ai/entity/EntityGoalMoveTowardsTarget.java

@@ -37,19 +37,10 @@ public record EntityGoalMoveTowardsTarget(
                 return null;
             }
 
-            try {
             return new EntityGoalMoveTowardsTarget(
                     config.getDouble("speed"),
                     config.getDouble("maxDistance")
             );
-            } catch (Exception e) {
-                /*
-                Exceptions could be caused by configs having values of a wrong type,
-                invalid enum parameters, etc. Serializers shouldn't throw exceptions,
-                so we encapsulate them as null.
-                 */
-                return null;
-            }
         }
 
         @NotNull

eco-api/src/main/java/com/willfp/eco/core/entities/ai/entity/EntityGoalOpenDoors.java

@@ -34,18 +34,9 @@ public record EntityGoalOpenDoors(
                 return null;
             }
 
-            try {
             return new EntityGoalOpenDoors(
                     config.getBool("delayClosing")
             );
-            } catch (Exception e) {
-                /*
-                Exceptions could be caused by configs having values of a wrong type,
-                invalid enum parameters, etc. Serializers shouldn't throw exceptions,
-                so we encapsulate them as null.
-                 */
-                return null;
-            }
         }
 
         @NotNull

eco-api/src/main/java/com/willfp/eco/core/entities/ai/entity/EntityGoalPanic.java

@@ -34,18 +34,9 @@ public record EntityGoalPanic(
                 return null;
             }
 
-            try {
             return new EntityGoalPanic(
                     config.getDouble("speed")
             );
-            } catch (Exception e) {
-                /*
-                Exceptions could be caused by configs having values of a wrong type,
-                invalid enum parameters, etc. Serializers shouldn't throw exceptions,
-                so we encapsulate them as null.
-                 */
-                return null;
-            }
         }
 
         @NotNull

eco-api/src/main/java/com/willfp/eco/core/entities/ai/entity/EntityGoalRandomStroll.java

@@ -40,20 +40,11 @@ public record EntityGoalRandomStroll(
                 return null;
             }
 
-            try {
             return new EntityGoalRandomStroll(
                     config.getDouble("speed"),
                     config.getInt("interval"),
                     config.getBool("canDespawn")
             );
-            } catch (Exception e) {
-                /*
-                Exceptions could be caused by configs having values of a wrong type,
-                invalid enum parameters, etc. Serializers shouldn't throw exceptions,
-                so we encapsulate them as null.
-                 */
-                return null;
-            }
         }
 
         @NotNull

eco-api/src/main/java/com/willfp/eco/core/entities/ai/entity/EntityGoalRandomSwimming.java

@@ -37,19 +37,10 @@ public record EntityGoalRandomSwimming(
                 return null;
             }
 
-            try {
             return new EntityGoalRandomSwimming(
                     config.getDouble("speed"),
                     config.getInt("interval")
             );
-            } catch (Exception e) {
-                /*
-                Exceptions could be caused by configs having values of a wrong type,
-                invalid enum parameters, etc. Serializers shouldn't throw exceptions,
-                so we encapsulate them as null.
-                 */
-                return null;
-            }
         }
 
         @NotNull

eco-api/src/main/java/com/willfp/eco/core/entities/ai/entity/EntityGoalRangedAttack.java

@@ -45,21 +45,12 @@ public record EntityGoalRangedAttack(
                 return null;
             }
 
-            try {
             return new EntityGoalRangedAttack(
                     config.getDouble("speed"),
                     config.getInt("minInterval"),
                     config.getInt("maxInterval"),
                     config.getDouble("range")
             );
-            } catch (Exception e) {
-                /*
-                Exceptions could be caused by configs having values of a wrong type,
-                invalid enum parameters, etc. Serializers shouldn't throw exceptions,
-                so we encapsulate them as null.
-                 */
-                return null;
-            }
         }
 
         @NotNull

eco-api/src/main/java/com/willfp/eco/core/entities/ai/entity/EntityGoalRangedBowAttack.java

@@ -42,20 +42,11 @@ public record EntityGoalRangedBowAttack(
                 return null;
             }
 
-            try {
             return new EntityGoalRangedBowAttack(
                     config.getDouble("speed"),
                     config.getInt("interval"),
                     config.getDouble("range")
             );
-            } catch (Exception e) {
-                /*
-                Exceptions could be caused by configs having values of a wrong type,
-                invalid enum parameters, etc. Serializers shouldn't throw exceptions,
-                so we encapsulate them as null.
-                 */
-                return null;
-            }
         }
 
         @NotNull

eco-api/src/main/java/com/willfp/eco/core/entities/ai/entity/EntityGoalRangedCrossbowAttack.java

@@ -39,19 +39,10 @@ public record EntityGoalRangedCrossbowAttack(
                 return null;
             }
 
-            try {
             return new EntityGoalRangedCrossbowAttack(
                     config.getDouble("speed"),
                     config.getDouble("range")
             );
-            } catch (Exception e) {
-                /*
-                Exceptions could be caused by configs having values of a wrong type,
-                invalid enum parameters, etc. Serializers shouldn't throw exceptions,
-                so we encapsulate them as null.
-                 */
-                return null;
-            }
         }
 
         @NotNull

eco-api/src/main/java/com/willfp/eco/core/entities/ai/entity/EntityGoalStrollThroughVillage.java

@@ -34,18 +34,9 @@ public record EntityGoalStrollThroughVillage(
                 return null;
             }
 
-            try {
             return new EntityGoalStrollThroughVillage(
                     config.getInt("searchRange")
             );
-            } catch (Exception e) {
-                /*
-                Exceptions could be caused by configs having values of a wrong type,
-                invalid enum parameters, etc. Serializers shouldn't throw exceptions,
-                so we encapsulate them as null.
-                 */
-                return null;
-            }
         }
 
         @NotNull

eco-api/src/main/java/com/willfp/eco/core/entities/ai/entity/EntityGoalTempt.java

@@ -58,7 +58,6 @@ public record EntityGoalTempt(
                 return null;
             }
 
-            try {
             Collection<TestableItem> items = config.getStrings("items").stream()
                     .map(Items::lookup)
                     .filter(it -> !(it instanceof EmptyTestableItem))
@@ -69,14 +68,6 @@ public record EntityGoalTempt(
                     items,
                     config.getBool("canBeScared")
             );
-            } catch (Exception e) {
-                /*
-                Exceptions could be caused by configs having values of a wrong type,
-                invalid enum parameters, etc. Serializers shouldn't throw exceptions,
-                so we encapsulate them as null.
-                 */
-                return null;
-            }
         }
 
         @NotNull

eco-api/src/main/java/com/willfp/eco/core/entities/ai/entity/EntityGoalUseItem.java

@@ -48,7 +48,6 @@ public record EntityGoalUseItem(
                 return null;
             }
 
-            try {
             TestableEntity filter = Entities.lookup(config.getString("condition"));
 
             return new EntityGoalUseItem(
@@ -56,14 +55,6 @@ public record EntityGoalUseItem(
                     Sound.valueOf(config.getString("sound").toUpperCase()),
                     filter::matches
             );
-            } catch (Exception e) {
-                /*
-                Exceptions could be caused by configs having values of a wrong type,
-                invalid enum parameters, etc. Serializers shouldn't throw exceptions,
-                so we encapsulate them as null.
-                 */
-                return null;
-            }
         }
 
         @NotNull

eco-api/src/main/java/com/willfp/eco/core/entities/ai/entity/EntityGoalWaterAvoidingRandomFlying.java

@@ -34,18 +34,9 @@ public record EntityGoalWaterAvoidingRandomFlying(
                 return null;
             }
 
-            try {
             return new EntityGoalWaterAvoidingRandomFlying(
                     config.getDouble("speed")
             );
-            } catch (Exception e) {
-                /*
-                Exceptions could be caused by configs having values of a wrong type,
-                invalid enum parameters, etc. Serializers shouldn't throw exceptions,
-                so we encapsulate them as null.
-                 */
-                return null;
-            }
         }
 
         @NotNull

eco-api/src/main/java/com/willfp/eco/core/entities/ai/entity/EntityGoalWaterAvoidingRandomStroll.java

@@ -37,19 +37,10 @@ public record EntityGoalWaterAvoidingRandomStroll(
                 return null;
             }
 
-            try {
             return new EntityGoalWaterAvoidingRandomStroll(
                     config.getDouble("speed"),
                     config.getDouble("chance")
             );
-            } catch (Exception e) {
-                /*
-                Exceptions could be caused by configs having values of a wrong type,
-                invalid enum parameters, etc. Serializers shouldn't throw exceptions,
-                so we encapsulate them as null.
-                 */
-                return null;
-            }
         }
 
         @NotNull

eco-api/src/main/java/com/willfp/eco/core/entities/ai/entity/EntityGoalWolfBeg.java

@@ -34,18 +34,9 @@ public record EntityGoalWolfBeg(
                 return null;
             }
 
-            try {
             return new EntityGoalWolfBeg(
                     config.getDouble("distance")
             );
-            } catch (Exception e) {
-                /*
-                Exceptions could be caused by configs having values of a wrong type,
-                invalid enum parameters, etc. Serializers shouldn't throw exceptions,
-                so we encapsulate them as null.
-                 */
-                return null;
-            }
         }
 
         @NotNull

eco-api/src/main/java/com/willfp/eco/core/entities/ai/target/TargetGoalHurtBy.java

@@ -37,18 +37,9 @@ public record TargetGoalHurtBy(
                 return null;
             }
 
-            try {
             return new TargetGoalHurtBy(
                     Entities.lookup(config.getString("blacklist"))
             );
-            } catch (Exception e) {
-                /*
-                Exceptions could be caused by configs having values of a wrong type,
-                invalid enum parameters, etc. Serializers shouldn't throw exceptions,
-                so we encapsulate them as null.
-                 */
-                return null;
-            }
         }
 
         @NotNull

eco-api/src/main/java/com/willfp/eco/core/entities/ai/target/TargetGoalNearestAttackable.java

@@ -63,7 +63,6 @@ public record TargetGoalNearestAttackable(
                 return null;
             }
 
-            try {
             if (config.has("targetFilter")) {
                 TestableEntity filter = Entities.lookup(config.getString("targetFilter"));
 
@@ -82,14 +81,6 @@ public record TargetGoalNearestAttackable(
                         config.getInt("reciprocalChance")
                 );
             }
-            } catch (Exception e) {
-                /*
-                Exceptions could be caused by configs having values of a wrong type,
-                invalid enum parameters, etc. Serializers shouldn't throw exceptions,
-                so we encapsulate them as null.
-                 */
-                return null;
-            }
         }
 
         @NotNull

eco-api/src/main/java/com/willfp/eco/core/entities/ai/target/TargetGoalNearestAttackableWitch.java

@@ -63,7 +63,6 @@ public record TargetGoalNearestAttackableWitch(
                 return null;
             }
 
-            try {
             if (config.has("targetFilter")) {
                 TestableEntity filter = Entities.lookup(config.getString("targetFilter"));
 
@@ -82,14 +81,6 @@ public record TargetGoalNearestAttackableWitch(
                         config.getInt("reciprocalChance")
                 );
             }
-            } catch (Exception e) {
-                /*
-                Exceptions could be caused by configs having values of a wrong type,
-                invalid enum parameters, etc. Serializers shouldn't throw exceptions,
-                so we encapsulate them as null.
-                 */
-                return null;
-            }
         }
 
         @NotNull

eco-api/src/main/java/com/willfp/eco/core/entities/ai/target/TargetGoalNearestHealableRaider.java

@@ -53,7 +53,6 @@ public record TargetGoalNearestHealableRaider(
                 return null;
             }
 
-            try {
             if (config.has("targetFilter")) {
                 TestableEntity filter = Entities.lookup(config.getString("targetFilter"));
 
@@ -68,14 +67,6 @@ public record TargetGoalNearestHealableRaider(
                         config.getBool("checkVisibility")
                 );
             }
-            } catch (Exception e) {
-                /*
-                Exceptions could be caused by configs having values of a wrong type,
-                invalid enum parameters, etc. Serializers shouldn't throw exceptions,
-                so we encapsulate them as null.
-                 */
-                return null;
-            }
         }
 
         @NotNull

eco-api/src/main/java/com/willfp/eco/core/entities/ai/target/TargetGoalNonTameRandom.java

@@ -53,7 +53,6 @@ public record TargetGoalNonTameRandom(
                 return null;
             }
 
-            try {
             if (config.has("targetFilter")) {
                 TestableEntity filter = Entities.lookup(config.getString("targetFilter"));
 
@@ -68,14 +67,6 @@ public record TargetGoalNonTameRandom(
                         config.getBool("checkVisibility")
                 );
             }
-            } catch (Exception e) {
-                /*
-                Exceptions could be caused by configs having values of a wrong type,
-                invalid enum parameters, etc. Serializers shouldn't throw exceptions,
-                so we encapsulate them as null.
-                 */
-                return null;
-            }
         }
 
         @NotNull

eco-api/src/main/java/com/willfp/eco/core/entities/ai/target/TargetGoalResetUniversalAnger.java

@@ -36,18 +36,9 @@ public record TargetGoalResetUniversalAnger(
                 return null;
             }
 
-            try {
             return new TargetGoalResetUniversalAnger(
                     config.getBool("triggerOthers")
             );
-            } catch (Exception e) {
-                /*
-                Exceptions could be caused by configs having values of a wrong type,
-                invalid enum parameters, etc. Serializers shouldn't throw exceptions,
-                so we encapsulate them as null.
-                 */
-                return null;
-            }
         }
 
         @NotNull

eco-api/src/main/java/com/willfp/eco/core/events/EventManager.java

@@ -1,5 +1,6 @@
 package com.willfp.eco.core.events;
 
+import com.willfp.eco.core.packet.PacketListener;
 import org.bukkit.event.Listener;
 import org.jetbrains.annotations.NotNull;
 
@@ -25,4 +26,11 @@ public interface EventManager {
      * Unregister all listeners associated with the plugin.
      */
     void unregisterAllListeners();
+
+    /**
+     * Register a packet listener.
+     *
+     * @param listener The listener.
+     */
+    void registerPacketListener(@NotNull PacketListener listener);
 }

eco-api/src/main/java/com/willfp/eco/core/gui/menu/MenuBuilder.java

@@ -139,7 +139,7 @@ public interface MenuBuilder extends PageBuilder {
      * @return The builder.
      */
     default MenuBuilder maxPages(@NotNull final Function<Player, Integer> pages) {
-        return onRender((player, menu) -> menu.setState(player, Page.MAX_PAGE_KEY, pages.apply(player)));
+        return this.onRender((player, menu) -> menu.setState(player, Page.MAX_PAGE_KEY, pages.apply(player)));
     }
 
     /**

eco-api/src/main/java/com/willfp/eco/core/gui/slot/ConfigSlot.java

@@ -1,12 +1,14 @@
 package com.willfp.eco.core.gui.slot;
 
 import com.willfp.eco.core.config.interfaces.Config;
+import com.willfp.eco.core.fast.FastItemStack;
 import com.willfp.eco.core.gui.slot.functional.SlotHandler;
 import com.willfp.eco.core.items.Items;
 import com.willfp.eco.util.StringUtils;
 import org.bukkit.Bukkit;
 import org.bukkit.entity.Player;
 import org.bukkit.event.inventory.ClickType;
+import org.bukkit.inventory.ItemStack;
 import org.jetbrains.annotations.NotNull;
 
 import java.util.ArrayList;
@@ -37,7 +39,25 @@ public class ConfigSlot extends CustomSlot {
     public ConfigSlot(@NotNull final Config config) {
         this.config = config;
 
-        SlotBuilder builder = Slot.builder(Items.lookup(config.getString("item")));
+        ItemStack item = Items.lookup(config.getString("item")).getItem();
+
+        SlotBuilder builder = Slot.builder((player, menu) -> {
+            if (!config.has("lore")) {
+                return item;
+            } else {
+                FastItemStack fast = FastItemStack.wrap(item.clone());
+                List<String> newLore = new ArrayList<>(fast.getLore());
+                newLore.addAll(
+                        StringUtils.formatList(
+                                config.getStrings("lore"),
+                                player,
+                                StringUtils.FormatOption.WITH_PLACEHOLDERS
+                        )
+                );
+                fast.setLore(newLore);
+                return fast.unwrap();
+            }
+        });
 
         for (ClickType clickType : ClickType.values()) {
             builder.onClick(

eco-api/src/main/java/com/willfp/eco/core/gui/slot/CustomSlot.java

@@ -4,6 +4,7 @@ import com.willfp.eco.core.gui.menu.Menu;
 import org.bukkit.entity.Player;
 import org.bukkit.inventory.ItemStack;
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
 /**
  * Base class for custom slot implementations.
@@ -31,7 +32,7 @@ public abstract class CustomSlot implements Slot {
     }
 
     @Override
-    public @NotNull ItemStack getItemStack(@NotNull final Player player) {
+    public final @NotNull ItemStack getItemStack(@NotNull final Player player) {
         if (delegate == null) {
             throw new IllegalStateException("Custom Slot was not initialized!");
         }
@@ -40,7 +41,7 @@ public abstract class CustomSlot implements Slot {
     }
 
     @Override
-    public boolean isCaptive(@NotNull final Player player,
+    public final boolean isCaptive(@NotNull final Player player,
                                    @NotNull final Menu menu) {
         if (delegate == null) {
             throw new IllegalStateException("Custom Slot was not initialized!");
@@ -50,7 +51,18 @@ public abstract class CustomSlot implements Slot {
     }
 
     @Override
-    public boolean isCaptiveFromEmpty() {
+    public final boolean isAllowedCaptive(@NotNull final Player player,
+                                          @NotNull final Menu menu,
+                                          @Nullable final ItemStack itemStack) {
+        if (delegate == null) {
+            throw new IllegalStateException("Custom Slot was not initialized!");
+        }
+
+        return delegate.isAllowedCaptive(player, menu, itemStack);
+    }
+
+    @Override
+    public final boolean isCaptiveFromEmpty() {
         if (delegate == null) {
             throw new IllegalStateException("Custom Slot was not initialized!");
         }
@@ -59,7 +71,7 @@ public abstract class CustomSlot implements Slot {
     }
 
     @Override
-    public final Slot getActionableSlot(@NotNull final Player player,
+    public final @NotNull Slot getActionableSlot(@NotNull final Player player,
                                                  @NotNull final Menu menu) {
         return delegate;
     }

eco-api/src/main/java/com/willfp/eco/core/gui/slot/ReactiveSlot.java

@@ -5,6 +5,7 @@ import org.bukkit.Material;
 import org.bukkit.entity.Player;
 import org.bukkit.inventory.ItemStack;
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
 /**
  * Base class for custom slot implementations.
@@ -34,11 +35,18 @@ public abstract class ReactiveSlot implements Slot {
     }
 
     @Override
-    public boolean isCaptive(@NotNull final Player player,
+    public final boolean isCaptive(@NotNull final Player player,
                                    @NotNull final Menu menu) {
         return getSlot(player, menu).isCaptive(player, menu);
     }
 
+    @Override
+    public final boolean isAllowedCaptive(@NotNull final Player player,
+                                          @NotNull final Menu menu,
+                                          @Nullable final ItemStack itemStack) {
+        return getSlot(player, menu).isAllowedCaptive(player, menu, itemStack);
+    }
+
     @Override
     public final @NotNull Slot getActionableSlot(@NotNull final Player player,
                                                  @NotNull final Menu menu) {

eco-api/src/main/java/com/willfp/eco/core/gui/slot/Slot.java

@@ -9,6 +9,7 @@ import org.bukkit.Material;
 import org.bukkit.entity.Player;
 import org.bukkit.inventory.ItemStack;
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
 import java.util.function.Function;
 
@@ -45,6 +46,20 @@ public interface Slot extends GUIComponent {
         return false;
     }
 
+    /**
+     * If the slot allows a certain item to be placed in it.
+     *
+     * @param player    The player.
+     * @param menu      The menu.
+     * @param itemStack The item; use null if the item is unknown.
+     * @return If captive.
+     */
+    default boolean isAllowedCaptive(@NotNull final Player player,
+                                     @NotNull final Menu menu,
+                                     @Nullable final ItemStack itemStack) {
+        return this.isCaptive(player, menu);
+    }
+
     /**
      * Get the actionable slot to be shown.
      * <p>

eco-api/src/main/java/com/willfp/eco/core/gui/slot/SlotBuilder.java

@@ -1,5 +1,6 @@
 package com.willfp.eco.core.gui.slot;
 
+import com.willfp.eco.core.gui.slot.functional.CaptiveFilter;
 import com.willfp.eco.core.gui.slot.functional.SlotHandler;
 import com.willfp.eco.core.gui.slot.functional.SlotModifier;
 import com.willfp.eco.core.gui.slot.functional.SlotUpdater;
@@ -143,7 +144,17 @@ public interface SlotBuilder {
      * @param predicate The predicate. Returns true when the slot should not be captive.
      * @return The builder.
      */
-    SlotBuilder notCaptiveFor(@NotNull Predicate<Player> predicate);
+    SlotBuilder notCaptiveFor(@NotNull final Predicate<Player> predicate);
+
+    /**
+     * Set a whitelist for allowed captive items.
+     *
+     * @param filter The filter.
+     * @return The builder.
+     */
+    default SlotBuilder setCaptiveFilter(@NotNull final CaptiveFilter filter) {
+        return this;
+    }
 
     /**
      * Set the ItemStack updater.

eco-api/src/main/java/com/willfp/eco/core/gui/slot/functional/CaptiveFilter.java

@@ -0,0 +1,25 @@
+package com.willfp.eco.core.gui.slot.functional;
+
+import com.willfp.eco.core.gui.menu.Menu;
+import org.bukkit.entity.Player;
+import org.bukkit.inventory.ItemStack;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+/**
+ * Interface to test if a captive slot is allowed to contain an item given a player and a menu.
+ */
+@FunctionalInterface
+public interface CaptiveFilter {
+    /**
+     * Get if allowed.
+     *
+     * @param player    The player.
+     * @param menu      The menu.
+     * @param itemStack The item.
+     * @return If captive.
+     */
+    boolean isAllowed(@NotNull Player player,
+                      @NotNull Menu menu,
+                      @Nullable ItemStack itemStack);
+}

eco-api/src/main/java/com/willfp/eco/core/integrations/guidetection/GUIDetectionIntegration.java

@@ -0,0 +1,18 @@
+package com.willfp.eco.core.integrations.guidetection;
+
+import com.willfp.eco.core.integrations.Integration;
+import org.bukkit.entity.Player;
+import org.jetbrains.annotations.NotNull;
+
+/**
+ * Wrapper class for GUI integrations.
+ */
+public interface GUIDetectionIntegration extends Integration {
+    /**
+     * Determine if a player is in a GUI.
+     *
+     * @param player The player.
+     * @return If the player is in a GUI.
+     */
+    boolean hasGUIOpen(@NotNull final Player player);
+}

eco-api/src/main/java/com/willfp/eco/core/integrations/guidetection/GUIDetectionManager.java

@@ -0,0 +1,52 @@
+package com.willfp.eco.core.integrations.guidetection;
+
+import com.willfp.eco.util.MenuUtils;
+import org.bukkit.entity.Player;
+import org.jetbrains.annotations.NotNull;
+
+import java.util.HashSet;
+import java.util.Set;
+
+/**
+ * Class to handle GUI detection.
+ */
+public final class GUIDetectionManager {
+    /**
+     * A set of all registered integrations.
+     */
+    private static final Set<GUIDetectionIntegration> REGISTERED = new HashSet<>();
+
+    /**
+     * Register a new integration.
+     *
+     * @param integration The integration to register.
+     */
+    public static void register(@NotNull final GUIDetectionIntegration integration) {
+        REGISTERED.removeIf(it -> it.getPluginName().equalsIgnoreCase(integration.getPluginName()));
+        REGISTERED.add(integration);
+    }
+
+    /**
+     * Get if a player is in a GUI.
+     *
+     * @param player The player.
+     * @return If the player has a GUI open.
+     */
+    public static boolean hasGUIOpen(@NotNull final Player player) {
+        if (MenuUtils.getOpenMenu(player) != null) {
+            return true;
+        }
+
+        for (GUIDetectionIntegration integration : REGISTERED) {
+            if (integration.hasGUIOpen(player)) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    private GUIDetectionManager() {
+        throw new UnsupportedOperationException("This is a utility class and cannot be instantiated");
+    }
+}

eco-api/src/main/java/com/willfp/eco/core/integrations/mcmmo/McmmoManager.java

@@ -33,10 +33,15 @@ public final class McmmoManager {
      * @return The bonus drop count.
      */
     public static int getBonusDropCount(@NotNull final Block block) {
+        int finalValue = 0;
         for (McmmoIntegration mcmmoIntegration : REGISTERED) {
-            return mcmmoIntegration.getBonusDropCount(block);
+            finalValue += mcmmoIntegration.getBonusDropCount(block);
+            
+
+
+            
         }
-        return 0;
+        return finalValue;
     }
 
     /**
@@ -47,7 +52,10 @@ public final class McmmoManager {
      */
     public static boolean isFake(@NotNull final Event event) {
         for (McmmoIntegration mcmmoIntegration : REGISTERED) {
-            return mcmmoIntegration.isFake(event);
+            if (mcmmoIntegration.isFake(event)) {
+                return true;
+            }
+
         }
         return false;
     }

eco-api/src/main/java/com/willfp/eco/core/integrations/placeholder/PlaceholderManager.java

@@ -1,13 +1,16 @@
 package com.willfp.eco.core.integrations.placeholder;
 
+import com.github.benmanes.caffeine.cache.Cache;
 import com.github.benmanes.caffeine.cache.Caffeine;
 import com.github.benmanes.caffeine.cache.LoadingCache;
 import com.willfp.eco.core.Eco;
 import com.willfp.eco.core.EcoPlugin;
 import com.willfp.eco.core.placeholder.AdditionalPlayer;
+import com.willfp.eco.core.placeholder.DynamicPlaceholder;
 import com.willfp.eco.core.placeholder.InjectablePlaceholder;
 import com.willfp.eco.core.placeholder.Placeholder;
 import com.willfp.eco.core.placeholder.PlaceholderInjectable;
+import com.willfp.eco.core.placeholder.PlayerDynamicPlaceholder;
 import com.willfp.eco.core.placeholder.PlayerPlaceholder;
 import com.willfp.eco.core.placeholder.PlayerStaticPlaceholder;
 import com.willfp.eco.core.placeholder.PlayerlessPlaceholder;
@@ -24,6 +27,7 @@ import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
+import java.util.Optional;
 import java.util.Set;
 import java.util.concurrent.TimeUnit;
 import java.util.regex.Matcher;
@@ -37,13 +41,20 @@ public final class PlaceholderManager {
     /**
      * All registered placeholders.
      */
-    private static final Map<EcoPlugin, Map<String, Placeholder>> REGISTERED_PLACEHOLDERS = new HashMap<>();
+    private static final Map<EcoPlugin, Map<Pattern, Placeholder>> REGISTERED_PLACEHOLDERS = new HashMap<>();
 
     /**
      * All registered placeholder integrations.
      */
     private static final Set<PlaceholderIntegration> REGISTERED_INTEGRATIONS = new HashSet<>();
 
+    /**
+     * Placeholder Lookup Cache.
+     */
+    private static final Cache<PlaceholderLookup, Optional<Placeholder>> PLACEHOLDER_LOOKUP_CACHE = Caffeine.newBuilder()
+            .expireAfterWrite(1, TimeUnit.SECONDS)
+            .build();
+
     /**
      * Placeholder Cache.
      */
@@ -51,10 +62,17 @@ public final class PlaceholderManager {
             .expireAfterWrite(50, TimeUnit.MILLISECONDS)
             .build(key -> key.entry.getValue(key.player));
 
+    /**
+     * Dynamic Placeholder Cache.
+     */
+    private static final LoadingCache<DynamicEntryWithPlayer, String> DYNAMIC_PLACEHOLDER_CACHE = Caffeine.newBuilder()
+            .expireAfterWrite(50, TimeUnit.MILLISECONDS)
+            .build(key -> key.entry.getValue(key.args, key.player));
+
     /**
      * The default PlaceholderAPI pattern; brought in for compatibility.
      */
-    private static final Pattern PATTERN = Pattern.compile("[%]([^% ]+)[%]");
+    private static final Pattern PATTERN = Pattern.compile("%([^% ]+)%");
 
     /**
      * Empty injectable object.
@@ -88,14 +106,17 @@ public final class PlaceholderManager {
      * @param placeholder The placeholder to register.
      */
     public static void registerPlaceholder(@NotNull final Placeholder placeholder) {
-        if (placeholder instanceof StaticPlaceholder) {
+        if (placeholder instanceof StaticPlaceholder || placeholder instanceof PlayerStaticPlaceholder) {
             throw new IllegalArgumentException("Static placeholders cannot be registered!");
         }
 
         EcoPlugin plugin = placeholder.getPlugin() == null ? Eco.get().getEcoPlugin() : placeholder.getPlugin();
-        Map<String, Placeholder> pluginPlaceholders = REGISTERED_PLACEHOLDERS
+
+        Map<Pattern, Placeholder> pluginPlaceholders = REGISTERED_PLACEHOLDERS
                 .getOrDefault(plugin, new HashMap<>());
-        pluginPlaceholders.put(placeholder.getIdentifier(), placeholder);
+
+        pluginPlaceholders.put(placeholder.getPattern(), placeholder);
+
         REGISTERED_PLACEHOLDERS.put(plugin, pluginPlaceholders);
     }
 
@@ -136,21 +157,47 @@ public final class PlaceholderManager {
     public static String getResult(@Nullable final Player player,
                                    @NotNull final String identifier,
                                    @Nullable final EcoPlugin plugin) {
+        // This is really janky, and it sucks, but it works so?
+        // Compensating for regex being slow so that's why we get it.
+        Placeholder placeholder = PLACEHOLDER_LOOKUP_CACHE.get(
+                new PlaceholderLookup(identifier, plugin),
+                (it) -> {
                     EcoPlugin owner = plugin == null ? Eco.get().getEcoPlugin() : plugin;
-        Placeholder placeholder = REGISTERED_PLACEHOLDERS.getOrDefault(owner, new HashMap<>()).get(identifier.toLowerCase());
 
-        if (placeholder == null && plugin != null) {
-            Placeholder alternate = REGISTERED_PLACEHOLDERS.getOrDefault(Eco.get().getEcoPlugin(), new HashMap<>())
-                    .get(identifier.toLowerCase());
-            if (alternate != null) {
-                placeholder = alternate;
+                    // I hate the streams API.
+                    Optional<Placeholder> found = REGISTERED_PLACEHOLDERS
+                            .getOrDefault(owner, new HashMap<>())
+                            .entrySet()
+                            .stream().filter(entry -> entry.getKey().matcher(identifier).matches())
+                            .map(Map.Entry::getValue)
+                            .findFirst();
+
+                    if (found.isEmpty() && plugin != null) {
+                        // Here we go again! Something about legacy support? I don't remember.
+                        // I won't touch it though, I'm scared of the placeholder system.
+                        found = REGISTERED_PLACEHOLDERS
+                                .getOrDefault(Eco.get().getEcoPlugin(), new HashMap<>())
+                                .entrySet()
+                                .stream().filter(entry -> entry.getKey().matcher(identifier).matches())
+                                .map(Map.Entry::getValue)
+                                .findFirst();
                     }
+
+                    return found;
                 }
+        ).orElse(null);
 
         if (placeholder == null) {
             return "";
         }
 
+        /*
+        This code here is *really* not very good. It's mega externalized logic hacked
+        together and made worse by the addition of dynamic placeholders. But it works,
+        and it means I don't have to rewrite the whole placeholder system. So it's
+        good enough for me.
+         */
+
         if (placeholder instanceof PlayerPlaceholder playerPlaceholder) {
             if (player == null) {
                 return "";
@@ -159,6 +206,14 @@ public final class PlaceholderManager {
             }
         } else if (placeholder instanceof PlayerlessPlaceholder playerlessPlaceholder) {
             return playerlessPlaceholder.getValue();
+        } else if (placeholder instanceof PlayerDynamicPlaceholder playerDynamicPlaceholder) {
+            if (player == null) {
+                return "";
+            } else {
+                return DYNAMIC_PLACEHOLDER_CACHE.get(new DynamicEntryWithPlayer(playerDynamicPlaceholder, identifier, player));
+            }
+        } else if (placeholder instanceof DynamicPlaceholder dynamicPlaceholder) {
+            return dynamicPlaceholder.getValue(identifier);
         } else {
             return "";
         }
@@ -245,8 +300,10 @@ public final class PlaceholderManager {
         for (PlaceholderIntegration integration : REGISTERED_INTEGRATIONS) {
             processed = integration.translate(processed, player);
         }
+
         for (InjectablePlaceholder injection : context.getPlaceholderInjections()) {
             // Do I know this is a bad way of doing this? Yes.
+            // I know it's deprecated, but it's fast.
             if (injection instanceof StaticPlaceholder placeholder) {
                 processed = processed.replace("%" + placeholder.getIdentifier() + "%", placeholder.getValue());
             } else if (injection instanceof PlayerStaticPlaceholder placeholder && player != null) {
@@ -280,11 +337,22 @@ public final class PlaceholderManager {
         return new ArrayList<>(found);
     }
 
+    private record PlaceholderLookup(@NotNull String identifier,
+                                     @Nullable EcoPlugin plugin) {
+
+    }
+
     private record EntryWithPlayer(@NotNull PlayerPlaceholder entry,
                                    @NotNull Player player) {
 
     }
 
+    private record DynamicEntryWithPlayer(@NotNull PlayerDynamicPlaceholder entry,
+                                          @NotNull String args,
+                                          @NotNull Player player) {
+
+    }
+
     private PlaceholderManager() {
         throw new UnsupportedOperationException("This is a utility class and cannot be instantiated");
     }

eco-api/src/main/java/com/willfp/eco/core/integrations/shop/ShopIntegration.java

@@ -1,6 +1,8 @@
 package com.willfp.eco.core.integrations.shop;
 
 import com.willfp.eco.core.integrations.Integration;
+import com.willfp.eco.core.price.Price;
+import com.willfp.eco.core.price.impl.PriceFree;
 import org.bukkit.entity.Player;
 import org.bukkit.event.Listener;
 import org.bukkit.inventory.ItemStack;
@@ -29,12 +31,41 @@ public interface ShopIntegration extends Integration {
         return null;
     }
 
+    /**
+     * Get if an item is sellable for a player.
+     *
+     * @param itemStack The item.
+     * @param player    The player.
+     * @return If sellable.
+     */
+    default boolean isSellable(@NotNull final ItemStack itemStack,
+                               @NotNull final Player player) {
+        return false;
+    }
+
+    /**
+     * Get the value of one of an item for a player.
+     * <p>
+     * For example, if you pass in a stack, it will only return the value of <b>one</b> item, not the full stack.
+     *
+     * @param itemStack The item.
+     * @param player    The player.
+     * @return The price.
+     */
+    @NotNull
+    default Price getUnitValue(@NotNull final ItemStack itemStack,
+                               @NotNull final Player player) {
+        return new PriceFree();
+    }
+
     /**
      * Get the price of an item.
      *
      * @param itemStack The item.
      * @return The price.
+     * @deprecated Use getValue instead.
      */
+    @Deprecated(since = "6.47.0", forRemoval = true)
     default double getPrice(@NotNull final ItemStack itemStack) {
         // Do nothing unless overridden.
         return 0.0;
@@ -46,9 +77,11 @@ public interface ShopIntegration extends Integration {
      * @param itemStack The item.
      * @param player    The player.
      * @return The price.
+     * @deprecated Use getValue instead.
      */
+    @Deprecated(since = "6.47.0", forRemoval = true)
     default double getPrice(@NotNull final ItemStack itemStack,
                             @NotNull final Player player) {
-        return getPrice(itemStack);
+        return getUnitValue(itemStack, player).getValue(player);
     }
 }

eco-api/src/main/java/com/willfp/eco/core/integrations/shop/ShopManager.java

@@ -1,5 +1,7 @@
 package com.willfp.eco.core.integrations.shop;
 
+import com.willfp.eco.core.price.Price;
+import com.willfp.eco.core.price.impl.PriceFree;
 import org.bukkit.entity.Player;
 import org.bukkit.inventory.ItemStack;
 import org.jetbrains.annotations.NotNull;
@@ -36,12 +38,57 @@ public final class ShopManager {
         }
     }
 
+    /**
+     * Get if an item is sellable for a player.
+     *
+     * @param itemStack The item.
+     * @param player    The player.
+     * @return If sellable.
+     */
+    public static boolean isSellable(@Nullable final ItemStack itemStack,
+                                     @NotNull final Player player) {
+        if (itemStack == null) {
+            return false;
+        }
+
+        for (ShopIntegration integration : REGISTERED) {
+            return integration.isSellable(itemStack, player);
+        }
+
+        return false;
+    }
+
+    /**
+     * Get the value of one of an item for a player.
+     * <p>
+     * For example, if you pass in a stack, it will only return the value of <b>one</b> item, not the full stack.
+     *
+     * @param itemStack The item.
+     * @param player    The player.
+     * @return The price.
+     */
+    @NotNull
+    public static Price getUnitValue(@Nullable final ItemStack itemStack,
+                                     @NotNull final Player player) {
+        if (itemStack == null) {
+            return new PriceFree();
+        }
+
+        for (ShopIntegration integration : REGISTERED) {
+            return integration.getUnitValue(itemStack, player);
+        }
+
+        return new PriceFree();
+    }
+
     /**
      * Get the price of an item.
      *
      * @param itemStack The item.
      * @return The price.
+     * @deprecated Use getValue instead. This will always return 0 as prices depend on players.
      */
+    @Deprecated(since = "6.47.0", forRemoval = true)
     public static double getItemPrice(@Nullable final ItemStack itemStack) {
         return getItemPrice(itemStack, null);
     }
@@ -52,19 +99,17 @@ public final class ShopManager {
      * @param itemStack The item.
      * @param player    The player.
      * @return The price.
+     * @deprecated Use getValue instead. Null players / null items will always return 0.
      */
+    @Deprecated(since = "6.47.0", forRemoval = true)
     public static double getItemPrice(@Nullable final ItemStack itemStack,
                                       @Nullable final Player player) {
-        if (itemStack == null) {
+        if (itemStack == null || player == null) {
             return 0.0;
         }
 
         for (ShopIntegration shopIntegration : REGISTERED) {
-            if (player == null) {
-                return shopIntegration.getPrice(itemStack);
-            } else {
-                return shopIntegration.getPrice(itemStack, player);
-            }
+            return shopIntegration.getUnitValue(itemStack, player).getValue(player, itemStack.getAmount());
         }
 
         return 0.0;

eco-api/src/main/java/com/willfp/eco/core/integrations/shop/ShopSellEvent.java

@@ -1,5 +1,7 @@
 package com.willfp.eco.core.integrations.shop;
 
+import com.willfp.eco.core.price.Price;
+import com.willfp.eco.core.price.impl.PriceEconomy;
 import org.bukkit.entity.Player;
 import org.bukkit.event.HandlerList;
 import org.bukkit.event.player.PlayerEvent;
@@ -19,7 +21,12 @@ public class ShopSellEvent extends PlayerEvent {
     /**
      * The sell price.
      */
-    private double price;
+    private Price price;
+
+    /**
+     * The price multiplier.
+     */
+    private double multiplier;
 
     /**
      * The item to be sold.
@@ -33,31 +40,64 @@ public class ShopSellEvent extends PlayerEvent {
      * @param who   The player.
      * @param price The price.
      * @param item  The item.
+     * @deprecated Use the price system instead.
      */
+    @Deprecated(since = "6.47.0", forRemoval = true)
     public ShopSellEvent(@NotNull final Player who,
                          final double price,
                          @Nullable final ItemStack item) {
+        this(who, new PriceEconomy(price), item);
+    }
+
+    /**
+     * Create new shop sell event.
+     *
+     * @param who   The player.
+     * @param price The price.
+     * @param item  The item.
+     */
+    public ShopSellEvent(@NotNull final Player who,
+                         @NotNull final Price price,
+                         @Nullable final ItemStack item) {
+        this(who, price, item, 1.0);
+    }
+
+    /**
+     * Create new shop sell event.
+     *
+     * @param who        The player.
+     * @param price      The price.
+     * @param item       The item.
+     * @param multiplier The multiplier.
+     */
+    public ShopSellEvent(@NotNull final Player who,
+                         @NotNull final Price price,
+                         @Nullable final ItemStack item,
+                         final double multiplier) {
         super(who);
 
         this.price = price;
         this.item = item;
+
+        this.multiplier = multiplier;
     }
 
     /**
-     * Get the price.
+     * Get the value.
      *
-     * @return The price.
+     * @return The value.
      */
-    public double getPrice() {
+    @NotNull
+    public Price getValue() {
         return this.price;
     }
 
     /**
-     * Set the price.
+     * Set the value.
      *
-     * @param price The price.
+     * @param price The value.
      */
-    public void setPrice(final double price) {
+    public void setValue(@NotNull final Price price) {
         this.price = price;
     }
 
@@ -81,6 +121,46 @@ public class ShopSellEvent extends PlayerEvent {
         return item != null;
     }
 
+    /**
+     * Get the price multiplier.
+     *
+     * @return The multiplier.
+     */
+    public double getMultiplier() {
+        return multiplier;
+    }
+
+    /**
+     * Set the price multiplier.
+     *
+     * @param multiplier The multiplier.
+     */
+    public void setMultiplier(final double multiplier) {
+        this.multiplier = multiplier;
+    }
+
+    /**
+     * Get the price.
+     *
+     * @return The price.
+     * @deprecated Use the price system instead.
+     */
+    @Deprecated(since = "6.47.0", forRemoval = true)
+    public double getPrice() {
+        return this.getValue().getValue(player);
+    }
+
+    /**
+     * Set the price.
+     *
+     * @param price The price.
+     * @deprecated Use the price system instead.
+     */
+    @Deprecated(since = "6.47.0", forRemoval = true)
+    public void setPrice(final double price) {
+        this.setValue(new PriceEconomy(price));
+    }
+
     /**
      * Bukkit parity.
      *

eco-api/src/main/java/com/willfp/eco/core/items/builder/AbstractItemStackBuilder.java

@@ -70,7 +70,7 @@ public abstract class AbstractItemStackBuilder<T extends ItemMeta, U extends Abs
 
     @Override
     public U setAmount(final int amount) {
-        Validate.isTrue(amount >= 1 && amount <= base.getMaxStackSize());
+        Validate.isTrue(amount >= 1);
         base.setAmount(amount);
         return (U) this;
     }

eco-api/src/main/java/com/willfp/eco/core/packet/Packet.java

@@ -0,0 +1,21 @@
+package com.willfp.eco.core.packet;
+
+import com.willfp.eco.core.Eco;
+import org.bukkit.entity.Player;
+import org.jetbrains.annotations.NotNull;
+
+/**
+ * Represents a packet.
+ *
+ * @param handle The NMS handle.
+ */
+public record Packet(@NotNull Object handle) {
+    /**
+     * Send to a player.
+     *
+     * @param player The player.
+     */
+    void send(@NotNull final Player player) {
+        Eco.get().sendPacket(player, this);
+    }
+}

eco-api/src/main/java/com/willfp/eco/core/packet/PacketEvent.java

@@ -0,0 +1,67 @@
+package com.willfp.eco.core.packet;
+
+import org.bukkit.entity.Player;
+import org.bukkit.event.Cancellable;
+import org.jetbrains.annotations.NotNull;
+
+/**
+ * Represents a packet being sent or received.
+ */
+public class PacketEvent implements Cancellable {
+    /**
+     * The packet.
+     */
+    private final Packet packet;
+
+    /**
+     * The player.
+     */
+    private final Player player;
+
+    /**
+     * If the event should be cancelled.
+     */
+    private boolean cancelled = false;
+
+    /**
+     * Create a new packet event.
+     *
+     * @param packet The packet.
+     * @param player The player.
+     */
+    public PacketEvent(@NotNull final Packet packet,
+                       @NotNull final Player player) {
+        this.packet = packet;
+        this.player = player;
+    }
+
+    /**
+     * Get the packet.
+     *
+     * @return The packet.
+     */
+    @NotNull
+    public Packet getPacket() {
+        return packet;
+    }
+
+    /**
+     * Get the player.
+     *
+     * @return The player.
+     */
+    @NotNull
+    public Player getPlayer() {
+        return player;
+    }
+
+    @Override
+    public boolean isCancelled() {
+        return cancelled;
+    }
+
+    @Override
+    public void setCancelled(final boolean cancelled) {
+        this.cancelled = cancelled;
+    }
+}

eco-api/src/main/java/com/willfp/eco/core/packet/PacketListener.java

@@ -0,0 +1,35 @@
+package com.willfp.eco.core.packet;
+
+import org.jetbrains.annotations.NotNull;
+
+/**
+ * Listens to packets.
+ */
+public interface PacketListener {
+    /**
+     * Called when a handle is sent.
+     *
+     * @param event The event.
+     */
+    default void onSend(@NotNull final PacketEvent event) {
+        // Override when needed.
+    }
+
+    /**
+     * Called when a handle is received.
+     *
+     * @param event The event.
+     */
+    default void onReceive(@NotNull final PacketEvent event) {
+        // Override when needed.
+    }
+
+    /**
+     * Get the priority of the listener.
+     *
+     * @return The priority.
+     */
+    default PacketPriority getPriority() {
+        return PacketPriority.NORMAL;
+    }
+}

eco-api/src/main/java/com/willfp/eco/core/packet/PacketPriority.java

@@ -0,0 +1,31 @@
+package com.willfp.eco.core.packet;
+
+/**
+ * The priority (order) of packet listeners.
+ */
+public enum PacketPriority {
+    /**
+     * Ran first.
+     */
+    LOWEST,
+
+    /**
+     * Ran second.
+     */
+    LOW,
+
+    /**
+     * Ran third.
+     */
+    NORMAL,
+
+    /**
+     * Ran fourth.
+     */
+    HIGH,
+
+    /**
+     * Ran last.
+     */
+    HIGHEST
+}

eco-api/src/main/java/com/willfp/eco/core/placeholder/DynamicPlaceholder.java

@@ -0,0 +1,102 @@
+package com.willfp.eco.core.placeholder;
+
+import com.willfp.eco.core.EcoPlugin;
+import com.willfp.eco.core.integrations.placeholder.PlaceholderManager;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.Objects;
+import java.util.function.Function;
+import java.util.regex.Pattern;
+
+/**
+ * A placeholder that does not require a player and supports dynamic styles.
+ */
+public final class DynamicPlaceholder implements Placeholder {
+    /**
+     * The placeholder pattern.
+     */
+    private final Pattern pattern;
+
+    /**
+     * The function to retrieve the output of the placeholder.
+     */
+    private final Function<String, String> function;
+
+    /**
+     * The plugin for the placeholder.
+     */
+    private final EcoPlugin plugin;
+
+    /**
+     * Create a new dynamic placeholder.
+     *
+     * @param plugin   The plugin.
+     * @param pattern  The pattern.
+     * @param function The function to retrieve the value.
+     */
+    public DynamicPlaceholder(@NotNull final EcoPlugin plugin,
+                              @NotNull final Pattern pattern,
+                              @NotNull final Function<String, String> function) {
+        this.plugin = plugin;
+        this.pattern = pattern;
+        this.function = function;
+    }
+
+    /**
+     * Get the value of the placeholder.
+     *
+     * @param args The args.
+     * @return The value.
+     */
+    @NotNull
+    public String getValue(@NotNull final String args) {
+        return function.apply(args);
+    }
+
+    /**
+     * Register the placeholder.
+     *
+     * @return The placeholder.
+     */
+    public DynamicPlaceholder register() {
+        PlaceholderManager.registerPlaceholder(this);
+        return this;
+    }
+
+    @Override
+    public @NotNull EcoPlugin getPlugin() {
+        return this.plugin;
+    }
+
+    @Override
+    @Deprecated
+    public @NotNull String getIdentifier() {
+        return "dynamic";
+    }
+
+    @NotNull
+    @Override
+    public Pattern getPattern() {
+        return this.pattern;
+    }
+
+    @Override
+    public boolean equals(@Nullable final Object o) {
+        if (this == o) {
+            return true;
+        }
+
+        if (!(o instanceof DynamicPlaceholder that)) {
+            return false;
+        }
+
+        return Objects.equals(this.getPattern(), that.getPattern())
+                && Objects.equals(this.getPlugin(), that.getPlugin());
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(this.getIdentifier(), this.getPlugin());
+    }
+}

eco-api/src/main/java/com/willfp/eco/core/placeholder/InjectablePlaceholder.java

@@ -2,13 +2,14 @@ package com.willfp.eco.core.placeholder;
 
 import com.willfp.eco.core.Eco;
 import com.willfp.eco.core.EcoPlugin;
+import org.jetbrains.annotations.NotNull;
 
 /**
  * Placeholders that can be injected into {@link PlaceholderInjectable} objects.
  */
 public sealed interface InjectablePlaceholder extends Placeholder permits PlayerStaticPlaceholder, StaticPlaceholder {
     @Override
-    default EcoPlugin getPlugin() {
+    default @NotNull EcoPlugin getPlugin() {
         return Eco.get().getEcoPlugin();
     }
 }

eco-api/src/main/java/com/willfp/eco/core/placeholder/Placeholder.java

@@ -1,16 +1,22 @@
 package com.willfp.eco.core.placeholder;
 
 import com.willfp.eco.core.EcoPlugin;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.regex.Pattern;
 
 /**
  * A placeholder represents a string that can hold a value.
  */
-public sealed interface Placeholder permits PlayerPlaceholder, PlayerlessPlaceholder, InjectablePlaceholder {
+public sealed interface Placeholder permits PlayerPlaceholder, PlayerlessPlaceholder,
+        DynamicPlaceholder, PlayerDynamicPlaceholder, InjectablePlaceholder {
     /**
      * Get the plugin that holds the placeholder.
      *
      * @return The plugin.
      */
+    @Nullable
     EcoPlugin getPlugin();
 
     /**
@@ -18,5 +24,16 @@ public sealed interface Placeholder permits PlayerPlaceholder, PlayerlessPlaceho
      *
      * @return The identifier.
      */
+    @NotNull
     String getIdentifier();
+
+    /**
+     * Get the pattern for the placeholder.
+     *
+     * @return The pattern.
+     */
+    @NotNull
+    default Pattern getPattern() {
+        return Pattern.compile(this.getIdentifier());
+    }
 }

eco-api/src/main/java/com/willfp/eco/core/placeholder/PlayerDynamicPlaceholder.java

@@ -0,0 +1,105 @@
+package com.willfp.eco.core.placeholder;
+
+import com.willfp.eco.core.EcoPlugin;
+import com.willfp.eco.core.integrations.placeholder.PlaceholderManager;
+import org.bukkit.entity.Player;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.Objects;
+import java.util.function.BiFunction;
+import java.util.regex.Pattern;
+
+/**
+ * A placeholder that does not require a player and supports dynamic styles.
+ */
+public final class PlayerDynamicPlaceholder implements Placeholder {
+    /**
+     * The placeholder pattern.
+     */
+    private final Pattern pattern;
+
+    /**
+     * The function to retrieve the output of the placeholder.
+     */
+    private final BiFunction<String, Player, String> function;
+
+    /**
+     * The plugin for the placeholder.
+     */
+    private final EcoPlugin plugin;
+
+    /**
+     * Create a new dynamic placeholder.
+     *
+     * @param plugin   The plugin.
+     * @param pattern  The pattern.
+     * @param function The function to retrieve the value.
+     */
+    public PlayerDynamicPlaceholder(@NotNull final EcoPlugin plugin,
+                                    @NotNull final Pattern pattern,
+                                    @NotNull final BiFunction<String, Player, String> function) {
+        this.plugin = plugin;
+        this.pattern = pattern;
+        this.function = function;
+    }
+
+    /**
+     * Get the value of the placeholder.
+     *
+     * @param args   The args.
+     * @param player The player.
+     * @return The value.
+     */
+    @NotNull
+    public String getValue(@NotNull final String args,
+                           @NotNull final Player player) {
+        return function.apply(args, player);
+    }
+
+    /**
+     * Register the placeholder.
+     *
+     * @return The placeholder.
+     */
+    public PlayerDynamicPlaceholder register() {
+        PlaceholderManager.registerPlaceholder(this);
+        return this;
+    }
+
+    @Override
+    public @NotNull EcoPlugin getPlugin() {
+        return this.plugin;
+    }
+
+    @Override
+    @Deprecated
+    public @NotNull String getIdentifier() {
+        return "dynamic";
+    }
+
+    @NotNull
+    @Override
+    public Pattern getPattern() {
+        return this.pattern;
+    }
+
+    @Override
+    public boolean equals(@Nullable final Object o) {
+        if (this == o) {
+            return true;
+        }
+
+        if (!(o instanceof PlayerDynamicPlaceholder that)) {
+            return false;
+        }
+
+        return Objects.equals(this.getPattern(), that.getPattern())
+                && Objects.equals(this.getPlugin(), that.getPlugin());
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(this.getIdentifier(), this.getPlugin());
+    }
+}

eco-api/src/main/java/com/willfp/eco/core/placeholder/PlayerPlaceholder.java

@@ -8,6 +8,7 @@ import org.jetbrains.annotations.Nullable;
 
 import java.util.Objects;
 import java.util.function.Function;
+import java.util.regex.Pattern;
 
 /**
  * A placeholder that requires a player.
@@ -18,6 +19,11 @@ public final class PlayerPlaceholder implements Placeholder {
      */
     private final String identifier;
 
+    /**
+     * The placeholder pattern.
+     */
+    private final Pattern pattern;
+
     /**
      * The function to retrieve the output of the placeholder given a player.
      */
@@ -40,6 +46,7 @@ public final class PlayerPlaceholder implements Placeholder {
                              @NotNull final Function<Player, String> function) {
         this.plugin = plugin;
         this.identifier = identifier;
+        this.pattern = Pattern.compile(identifier);
         this.function = function;
     }
 
@@ -49,6 +56,7 @@ public final class PlayerPlaceholder implements Placeholder {
      * @param player The player.
      * @return The value.
      */
+    @NotNull
     public String getValue(@NotNull final Player player) {
         return function.apply(player);
     }
@@ -64,15 +72,21 @@ public final class PlayerPlaceholder implements Placeholder {
     }
 
     @Override
-    public EcoPlugin getPlugin() {
+    public @NotNull EcoPlugin getPlugin() {
         return this.plugin;
     }
 
     @Override
-    public String getIdentifier() {
+    public @NotNull String getIdentifier() {
         return this.identifier;
     }
 
+    @NotNull
+    @Override
+    public Pattern getPattern() {
+        return this.pattern;
+    }
+
     @Override
     public boolean equals(@Nullable final Object o) {
         if (this == o) {

eco-api/src/main/java/com/willfp/eco/core/placeholder/PlayerStaticPlaceholder.java

@@ -6,6 +6,7 @@ import org.jetbrains.annotations.Nullable;
 
 import java.util.Objects;
 import java.util.function.Function;
+import java.util.regex.Pattern;
 
 /**
  * A placeholder that cannot be registered, and exists purely in injection.
@@ -16,6 +17,11 @@ public final class PlayerStaticPlaceholder implements InjectablePlaceholder {
      */
     private final String identifier;
 
+    /**
+     * The placeholder pattern.
+     */
+    private final Pattern pattern;
+
     /**
      * The function to retrieve the output of the placeholder.
      */
@@ -30,6 +36,7 @@ public final class PlayerStaticPlaceholder implements InjectablePlaceholder {
     public PlayerStaticPlaceholder(@NotNull final String identifier,
                                    @NotNull final Function<Player, String> function) {
         this.identifier = identifier;
+        this.pattern = Pattern.compile(identifier);
         this.function = function;
     }
 
@@ -39,15 +46,22 @@ public final class PlayerStaticPlaceholder implements InjectablePlaceholder {
      * @param player The player.
      * @return The value.
      */
+    @NotNull
     public String getValue(@NotNull final Player player) {
         return function.apply(player);
     }
 
     @Override
-    public String getIdentifier() {
+    public @NotNull String getIdentifier() {
         return this.identifier;
     }
 
+    @NotNull
+    @Override
+    public Pattern getPattern() {
+        return this.pattern;
+    }
+
     @Override
     public boolean equals(@Nullable final Object o) {
         if (this == o) {

eco-api/src/main/java/com/willfp/eco/core/placeholder/PlayerlessPlaceholder.java

@@ -7,16 +7,22 @@ import org.jetbrains.annotations.Nullable;
 
 import java.util.Objects;
 import java.util.function.Supplier;
+import java.util.regex.Pattern;
 
 /**
  * A placeholder that does not require a player.
  */
 public final class PlayerlessPlaceholder implements Placeholder {
     /**
-     * The name of the placeholder.
+     * The placeholder identifier.
      */
     private final String identifier;
 
+    /**
+     * The placeholder pattern.
+     */
+    private final Pattern pattern;
+
     /**
      * The function to retrieve the output of the placeholder.
      */
@@ -39,6 +45,7 @@ public final class PlayerlessPlaceholder implements Placeholder {
                                  @NotNull final Supplier<String> function) {
         this.plugin = plugin;
         this.identifier = identifier;
+        this.pattern = Pattern.compile(identifier);
         this.function = function;
     }
 
@@ -62,15 +69,21 @@ public final class PlayerlessPlaceholder implements Placeholder {
     }
 
     @Override
-    public EcoPlugin getPlugin() {
+    public @NotNull EcoPlugin getPlugin() {
         return this.plugin;
     }
 
     @Override
-    public String getIdentifier() {
+    public @NotNull String getIdentifier() {
         return this.identifier;
     }
 
+    @NotNull
+    @Override
+    public Pattern getPattern() {
+        return this.pattern;
+    }
+
     @Override
     public boolean equals(@Nullable final Object o) {
         if (this == o) {

eco-api/src/main/java/com/willfp/eco/core/placeholder/StaticPlaceholder.java

@@ -5,6 +5,7 @@ import org.jetbrains.annotations.Nullable;
 
 import java.util.Objects;
 import java.util.function.Supplier;
+import java.util.regex.Pattern;
 
 /**
  * A placeholder that cannot be registered, and exists purely in injection.
@@ -15,6 +16,11 @@ public final class StaticPlaceholder implements InjectablePlaceholder {
      */
     private final String identifier;
 
+    /**
+     * The placeholder pattern.
+     */
+    private final Pattern pattern;
+
     /**
      * The function to retrieve the output of the placeholder.
      */
@@ -29,6 +35,7 @@ public final class StaticPlaceholder implements InjectablePlaceholder {
     public StaticPlaceholder(@NotNull final String identifier,
                              @NotNull final Supplier<String> function) {
         this.identifier = identifier;
+        this.pattern = Pattern.compile(identifier);
         this.function = function;
     }
 
@@ -37,15 +44,22 @@ public final class StaticPlaceholder implements InjectablePlaceholder {
      *
      * @return The value.
      */
+    @NotNull
     public String getValue() {
         return function.get();
     }
 
     @Override
-    public String getIdentifier() {
+    public @NotNull String getIdentifier() {
         return this.identifier;
     }
 
+    @NotNull
+    @Override
+    public Pattern getPattern() {
+        return this.pattern;
+    }
+
     @Override
     public boolean equals(@Nullable final Object o) {
         if (this == o) {

eco-api/src/main/java/com/willfp/eco/core/price/CombinedDisplayPrice.java

@@ -0,0 +1,156 @@
+package com.willfp.eco.core.price;
+
+import org.bukkit.entity.Player;
+import org.jetbrains.annotations.NotNull;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * A group of {@link ConfiguredPrice}s in order to show them
+ * to players in one go.
+ */
+public final class CombinedDisplayPrice {
+    /**
+     * Maps configured prices to multipliers.
+     */
+    private final Map<ConfiguredPrice, Double> prices;
+
+    /**
+     * The player to format for.
+     */
+    private final Player player;
+
+    /**
+     * Initialize a new combined price mapping formatters to multipliers.
+     *
+     * @param player The player.
+     * @param prices The prices.
+     */
+    private CombinedDisplayPrice(@NotNull final Player player,
+                                 @NotNull final Map<ConfiguredPrice, Double> prices) {
+        this.player = player;
+        this.prices = prices;
+    }
+
+    /**
+     * Get the display strings.
+     *
+     * @return The display strings.
+     */
+    @NotNull
+    public String[] getDisplayStrings() {
+        List<String> displayStrings = new ArrayList<>();
+
+        for (Map.Entry<ConfiguredPrice, Double> entry : prices.entrySet()) {
+            displayStrings.add(entry.getKey().getDisplay(player, entry.getValue()));
+        }
+
+        return displayStrings.toArray(new String[0]);
+    }
+
+    /**
+     * The builder.
+     */
+    public static class Builder {
+        /**
+         * All multiplied prices.
+         */
+        private final List<MultipliedPrice> prices = new ArrayList<>();
+
+        /**
+         * The player.
+         */
+        private final Player player;
+
+        /**
+         * Create a new builder.
+         *
+         * @param player The player.
+         */
+        Builder(@NotNull final Player player) {
+            this.player = player;
+        }
+
+        /**
+         * Add a new price with a certain multiplier.
+         *
+         * @param price      The price.
+         * @param multiplier The multiplier.
+         * @return The builder.
+         */
+        @NotNull
+        public Builder add(@NotNull final ConfiguredPrice price,
+                           final double multiplier) {
+            prices.add(new MultipliedPrice(price, multiplier));
+            return this;
+        }
+
+
+        /**
+         * Add a new price.
+         *
+         * @param price The price.
+         * @return The builder.
+         */
+        @NotNull
+        public Builder add(@NotNull final ConfiguredPrice price) {
+            return this.add(price, 1D);
+        }
+
+        /**
+         * Build into a {@link CombinedDisplayPrice}.
+         *
+         * @return The combined price.
+         */
+        @NotNull
+        public CombinedDisplayPrice build() {
+            Map<ConfiguredPrice, Double> unitPrices = new HashMap<>();
+
+            // Take first configured price at each ID as the format for all prices with that ID.
+            for (MultipliedPrice price : prices) {
+                // Find the base price.
+                ConfiguredPrice base = unitPrices.keySet()
+                        .stream()
+                        .filter(it -> it.getIdentifier().equals(price.price().getIdentifier()))
+                        .findFirst()
+                        .orElse(price.price());
+
+                // Find the multiplier for a value of 1, e.g. a price that's worth 20 will be 0.05.
+                double unitMultiplier = 1 / base.getValue(player);
+
+                double currentMultiplier = unitPrices.getOrDefault(base, 0D);
+                currentMultiplier += unitMultiplier * price.price().getValue(player, price.multiplier());
+                unitPrices.put(base, currentMultiplier);
+            }
+
+            return new CombinedDisplayPrice(player, unitPrices);
+        }
+
+        /**
+         * A price with a multiplier.
+         *
+         * @param price      The price.
+         * @param multiplier The multiplier.
+         */
+        private record MultipliedPrice(
+                @NotNull ConfiguredPrice price,
+                double multiplier
+        ) {
+
+        }
+    }
+
+    /**
+     * Create a new builder for a player.
+     *
+     * @param player The player.
+     * @return The builder.
+     */
+    @NotNull
+    public static Builder builder(@NotNull final Player player) {
+        return new Builder(player);
+    }
+}

eco-api/src/main/java/com/willfp/eco/core/price/ConfiguredPrice.java

@@ -24,7 +24,7 @@ public final class ConfiguredPrice implements Price {
     /**
      * Free.
      */
-    private static final ConfiguredPrice FREE = new ConfiguredPrice(
+    public static final ConfiguredPrice FREE = new ConfiguredPrice(
             new PriceFree(),
             "Free"
     );
@@ -52,23 +52,27 @@ public final class ConfiguredPrice implements Price {
     }
 
     @Override
-    public boolean canAfford(@NotNull final Player player) {
-        return this.price.canAfford(player);
+    public boolean canAfford(@NotNull final Player player,
+                             final double multiplier) {
+        return this.price.canAfford(player, multiplier);
     }
 
     @Override
-    public void pay(@NotNull final Player player) {
-        this.price.pay(player);
+    public void pay(@NotNull final Player player,
+                    final double multiplier) {
+        this.price.pay(player, multiplier);
     }
 
     @Override
-    public void giveTo(@NotNull final Player player) {
-        this.price.giveTo(player);
+    public void giveTo(@NotNull final Player player,
+                       final double multiplier) {
+        this.price.giveTo(player, multiplier);
     }
 
     @Override
-    public double getValue(@NotNull final Player player) {
-        return this.price.getValue(player);
+    public double getValue(@NotNull final Player player,
+                           final double multiplier) {
+        return this.price.getValue(player, multiplier);
     }
 
     @Override
@@ -82,6 +86,11 @@ public final class ConfiguredPrice implements Price {
         this.price.setMultiplier(player, multiplier);
     }
 
+    @Override
+    public String getIdentifier() {
+        return this.price.getIdentifier();
+    }
+
     /**
      * Get the price that this delegates to.
      *
@@ -98,8 +107,20 @@ public final class ConfiguredPrice implements Price {
      * @return The display string.
      */
     public String getDisplay(@NotNull final Player player) {
+        return this.getDisplay(player, 1.0);
+    }
+
+    /**
+     * Get the display string for a player.
+     *
+     * @param player     The player.
+     * @param multiplier The multiplier.
+     * @return The display string.
+     */
+    public String getDisplay(@NotNull final Player player,
+                             final double multiplier) {
         return StringUtils.format(
-                formatString.replace("%value%", NumberUtils.format(this.getPrice().getValue(player))),
+                formatString.replace("%value%", NumberUtils.format(this.getPrice().getValue(player, multiplier))),
                 player,
                 StringUtils.FormatOption.WITH_PLACEHOLDERS
         );

eco-api/src/main/java/com/willfp/eco/core/price/Price.java

@@ -1,49 +1,150 @@
 package com.willfp.eco.core.price;
 
+import org.apache.commons.lang.NotImplementedException;
 import org.bukkit.entity.Player;
 import org.jetbrains.annotations.NotNull;
 
 /**
  * A price that a player should pay.
+ * <p>
+ * There are important implementation details:
+ * <p>
+ * For backwards compatibility, all methods are default, however you must override the following:
+ * <ul>
+ *     <li><code>canAfford(Player, double)</code></li>
+ *     <li><code>pay(Player, double)</code></li>
+ *     <li><code>giveTo(Player, double)</code></li>
+ *     <li><code>getValue(Player, double)</code></li>
+ *     <li><code>getMultiplier(Player)</code></li>
+ *     <li><code>setMultiplier(Player, double)</code></li>
+ * </ul>
+ * Otherwise, your implementation will throw {@link NotImplementedException}.
+ * <p>
+ * Also, getValue() should always return the value with player multipliers applied.
  */
 public interface Price {
     /**
-     * Get if the player can afford the price.
+     * Get if a player can afford to pay the price.
      *
      * @param player The player.
      * @return If the player can afford.
      */
-    boolean canAfford(@NotNull Player player);
+    default boolean canAfford(@NotNull final Player player) {
+        return this.canAfford(player, 1);
+    }
+
+    /**
+     * Get if a player can afford to pay x times the price.
+     *
+     * @param player     The player.
+     * @param multiplier The multiplier.
+     * @return If the player can afford.
+     */
+    default boolean canAfford(@NotNull final Player player,
+                              final double multiplier) {
+        throw new NotImplementedException("Override canAfford(Player, double) in your Price implementation!");
+    }
 
     /**
      * Make the player pay the price.
      * <p>
-     * Only run this if the player can afford the price.
+     * Check canAfford first.
      *
      * @param player The player.
      */
-    void pay(@NotNull Player player);
-
-    /**
-     * Give the value of the price to the player.
-     * <p>
-     * You should override this method, it's only marked as default for
-     * backwards compatibility purposes.
-     *
-     * @param player The player.
-     */
-    default void giveTo(@NotNull Player player) {
-        // Override when needed.
+    default void pay(@NotNull final Player player) {
+        this.pay(player, 1);
     }
 
     /**
-     * If the price is backed by a value, get it here.
+     * Make the player pay the price x times.
+     * <p>
+     * Check canAfford first.
+     *
+     * @param player     The player.
+     * @param multiplier The multiplier.
+     */
+    default void pay(@NotNull final Player player,
+                     final double multiplier) {
+        throw new NotImplementedException("Override pay(Player, double) in your Price implementation!");
+    }
+
+    /**
+     * Give the price to the player.
+     *
+     * @param player The player.
+     */
+    default void giveTo(@NotNull final Player player) {
+        this.giveTo(player, 1);
+    }
+
+    /**
+     * Give the price to the player x times.
+     *
+     * @param player     The player.
+     * @param multiplier The multiplier.
+     */
+    default void giveTo(@NotNull final Player player,
+                        final double multiplier) {
+        throw new NotImplementedException("Override giveTo(Player, double) in your Price implementation!");
+    }
+
+    /**
+     * Get the numerical value that backs this price.
      *
      * @param player The player.
      * @return The value.
      */
     default double getValue(@NotNull final Player player) {
-        return 0;
+        return getValue(player, 1);
+    }
+
+    /**
+     * Get the numeral value that backs this price multiplied x times.
+     *
+     * @param player     The player.
+     * @param multiplier The multiplier.
+     * @return The value.
+     */
+    default double getValue(@NotNull final Player player,
+                            final double multiplier) {
+        throw new NotImplementedException("Override getValue(Player, double) in your Price implementation!");
+    }
+
+    /**
+     * Get the value multiplier for the player.
+     *
+     * @param player The player.
+     * @return The multiplier.
+     */
+    default double getMultiplier(@NotNull final Player player) {
+        return 1;
+    }
+
+    /**
+     * Set the value multiplier for the player.
+     *
+     * @param player     The player.
+     * @param multiplier The multiplier.
+     */
+    default void setMultiplier(@NotNull final Player player,
+                               final double multiplier) {
+        throw new NotImplementedException("Override setMultiplier(Player, double) in your Price implementation!");
+    }
+
+    /**
+     * Get the identifier of this price (as type/instance checks break with delegation,
+     * this is used for combining prices, etc.)
+     * <p>
+     * By default, this uses the class name, but it's good practice to override this.
+     * <p>
+     * It's also good practice to prefix your identifiers with some kind of namespace or
+     * internal ID, in order to prevent conflicts.
+     *
+     * @return The identifier.
+     */
+    default String getIdentifier() {
+        return this.getClass().getName();
     }
 
     /**
@@ -61,31 +162,10 @@ public interface Price {
      * If the price is backed by a value, set it here.
      *
      * @param value The value.
-     * @deprecated Values shouldn't be fixed.
+     * @deprecated Values shouldn't be fixed. This method should never work.
      */
     @Deprecated(since = "6.45.0", forRemoval = true)
     default void setValue(final double value) {
         // Override when needed.
     }
-
-    /**
-     * Get the price multiplier for a player.
-     *
-     * @param player The player.
-     * @return The value.
-     */
-    default double getMultiplier(@NotNull final Player player) {
-        return 1;
-    }
-
-    /**
-     * Set the price multiplier for a player.
-     *
-     * @param player     The        player.
-     * @param multiplier The multiplier.
-     */
-    default void setMultiplier(@NotNull final Player player,
-                               final double multiplier) {
-        // Override when needed.
-    }
 }

eco-api/src/main/java/com/willfp/eco/core/price/Prices.java

@@ -71,10 +71,6 @@ public final class Prices {
                 ctx
         );
 
-        if (function.apply(context) <= 0) {
-            return new PriceFree();
-        }
-
         // Default to economy
         if (priceName == null) {
             return new PriceEconomy(context, function);

eco-api/src/main/java/com/willfp/eco/core/price/impl/PriceEconomy.java

@@ -52,23 +52,27 @@ public final class PriceEconomy implements Price {
     }
 
     @Override
-    public boolean canAfford(@NotNull final Player player) {
-        return EconomyManager.getBalance(player) >= getValue(player);
+    public boolean canAfford(@NotNull final Player player,
+                             final double multiplier) {
+        return EconomyManager.getBalance(player) >= getValue(player, multiplier);
     }
 
     @Override
-    public void pay(@NotNull final Player player) {
-        EconomyManager.removeMoney(player, getValue(player));
+    public void pay(@NotNull final Player player,
+                    final double multiplier) {
+        EconomyManager.removeMoney(player, getValue(player, multiplier));
     }
 
     @Override
-    public void giveTo(@NotNull final Player player) {
-        EconomyManager.giveMoney(player, getValue(player));
+    public void giveTo(@NotNull final Player player,
+                       final double multiplier) {
+        EconomyManager.giveMoney(player, getValue(player, multiplier));
     }
 
     @Override
-    public double getValue(@NotNull final Player player) {
-        return this.function.apply(MathContext.copyWithPlayer(baseContext, player)) * getMultiplier(player);
+    public double getValue(@NotNull final Player player,
+                           final double multiplier) {
+        return this.function.apply(MathContext.copyWithPlayer(baseContext, player)) * getMultiplier(player) * multiplier;
     }
 
     @Override
@@ -81,4 +85,9 @@ public final class PriceEconomy implements Price {
                               final double multiplier) {
         this.multipliers.put(player.getUniqueId(), multiplier);
     }
+
+    @Override
+    public String getIdentifier() {
+        return "eco:economy";
+    }
 }

eco-api/src/main/java/com/willfp/eco/core/price/impl/PriceFree.java

@@ -16,12 +16,42 @@ public final class PriceFree implements Price {
     }
 
     @Override
-    public boolean canAfford(@NotNull final Player player) {
+    public boolean canAfford(@NotNull final Player player,
+                             final double multiplier) {
         return true;
     }
 
     @Override
-    public void pay(@NotNull final Player player) {
-        // Do nothing.
+    public void pay(@NotNull final Player player,
+                    final double multiplier) {
+        // Nothing.
+    }
+
+    @Override
+    public void giveTo(@NotNull final Player player,
+                       final double multiplier) {
+        // Nothing.
+    }
+
+    @Override
+    public double getMultiplier(@NotNull final Player player) {
+        return 1.0;
+    }
+
+    @Override
+    public void setMultiplier(@NotNull final Player player,
+                              final double multiplier) {
+        // Nothing.
+    }
+
+    @Override
+    public double getValue(@NotNull final Player player,
+                           final double multiplier) {
+        return 0;
+    }
+
+    @Override
+    public String getIdentifier() {
+        return "eco:free";
     }
 }

eco-api/src/main/java/com/willfp/eco/core/price/impl/PriceItem.java

@@ -1,6 +1,7 @@
 package com.willfp.eco.core.price.impl;
 
 import com.willfp.eco.core.drops.DropQueue;
+import com.willfp.eco.core.items.HashedItem;
 import com.willfp.eco.core.items.TestableItem;
 import com.willfp.eco.core.math.MathContext;
 import com.willfp.eco.core.price.Price;
@@ -74,8 +75,9 @@ public final class PriceItem implements Price {
     }
 
     @Override
-    public boolean canAfford(@NotNull final Player player) {
-        int toRemove = (int) getValue(player);
+    public boolean canAfford(@NotNull final Player player,
+                             final double multiplier) {
+        int toRemove = (int) getValue(player, multiplier);
         if (toRemove <= 0) {
             return true;
         }
@@ -92,8 +94,9 @@ public final class PriceItem implements Price {
     }
 
     @Override
-    public void pay(@NotNull final Player player) {
-        int toRemove = (int) getValue(player);
+    public void pay(@NotNull final Player player,
+                    final double multiplier) {
+        int toRemove = (int) getValue(player, multiplier);
         int count = 0;
 
         for (ItemStack itemStack : player.getInventory().getContents()) {
@@ -119,9 +122,10 @@ public final class PriceItem implements Price {
     }
 
     @Override
-    public void giveTo(@NotNull final Player player) {
+    public void giveTo(@NotNull final Player player,
+                       final double multiplier) {
         ItemStack itemStack = item.getItem().clone();
-        itemStack.setAmount((int) getValue(player));
+        itemStack.setAmount((int) getValue(player, multiplier));
 
         new DropQueue(player)
                 .addItem(itemStack)
@@ -130,9 +134,11 @@ public final class PriceItem implements Price {
     }
 
     @Override
-    public double getValue(@NotNull final Player player) {
+    public double getValue(@NotNull final Player player,
+                           final double multiplier) {
         return Math.toIntExact(Math.round(
-                this.function.apply(MathContext.copyWithPlayer(baseContext, player)) * getMultiplier(player)
+                this.function.apply(MathContext.copyWithPlayer(baseContext, player))
+                        * getMultiplier(player) * multiplier
         ));
     }
 
@@ -146,4 +152,9 @@ public final class PriceItem implements Price {
                               final double multiplier) {
         this.multipliers.put(player.getUniqueId(), multiplier);
     }
+
+    @Override
+    public String getIdentifier() {
+        return "eco:item-" + HashedItem.of(this.item.getItem()).getHash();
+    }
 }

eco-api/src/main/java/com/willfp/eco/core/proxy/ProxyConstants.java

@@ -21,7 +21,8 @@ public final class ProxyConstants {
             "v1_17_R1",
             "v1_18_R1",
             "v1_18_R2",
-            "v1_19_R1"
+            "v1_19_R1",
+            "v1_19_R2"
     );
 
     private ProxyConstants() {

eco-api/src/main/java/com/willfp/eco/core/sound/PlayableSound.java

@@ -85,8 +85,8 @@ public record PlayableSound(@NotNull Sound sound,
             try {
                 Sound sound = Sound.valueOf(config.getString("sound").toUpperCase());
 
-                double pitch = Objects.requireNonNullElse(config.getDouble("pitch"), 1.0);
-                double volume = Objects.requireNonNullElse(config.getDouble("volume"), 1.0);
+                double pitch = Objects.requireNonNullElse(config.getDoubleOrNull("pitch"), 1.0);
+                double volume = Objects.requireNonNullElse(config.getDoubleOrNull("volume"), 1.0);
 
                 return new PlayableSound(
                         sound,

eco-api/src/main/java/com/willfp/eco/util/DurabilityUtils.java

@@ -16,6 +16,8 @@ import org.jetbrains.annotations.NotNull;
 /**
  * Utilities / API methods for item durability.
  */
+// Have to suppress casts to ItemMeta because the methods don't exist for some older versions that eco supports.
+@SuppressWarnings("RedundantCast")
 public final class DurabilityUtils {
     /**
      * Damage an item in a player's inventory.

eco-api/src/main/java/com/willfp/eco/util/StringUtils.java

@@ -579,7 +579,7 @@ public final class StringUtils {
      *
      * @param lookup The lookup string.
      * @return An array of tokens to be processed.
-     * @author Shawn (https://stackoverflow.com/questions/70606170/split-a-list-on-spaces-and-group-quoted-characters/70606653#70606653)
+     * @author Shawn (<a href="https://stackoverflow.com/questions/70606170/split-a-list-on-spaces-and-group-quoted-characters/70606653#70606653">...</a>)
      */
     @NotNull
     public static String[] parseTokens(@NotNull final String lookup) {

eco-api/src/main/kotlin/com/willfp/eco/core/commands/CommandHelpers.kt

@@ -4,9 +4,14 @@ package com.willfp.eco.core.commands
 
 import com.willfp.eco.core.EcoPlugin
 import com.willfp.eco.core.command.CommandBase
+import com.willfp.eco.core.command.NotificationException
 import com.willfp.eco.core.command.impl.PluginCommand
 import com.willfp.eco.core.command.impl.Subcommand
+import org.bukkit.Bukkit
+import org.bukkit.OfflinePlayer
 import org.bukkit.command.CommandSender
+import org.bukkit.entity.Player
+import java.util.function.Predicate
 
 /**
  * Helper class for creating commands with builders.
@@ -140,3 +145,92 @@ fun CommandBase.addSubcommand(
     init(command)
     return command
 }
+
+/**
+ * Throws an exception containing a langYml key if obj is null.
+ * <p>The {@link CommandBase#onExecute(CommandSender, List) onExecute } in PluginCommand and Subcommand
+ * automatically handles sending the message to the sender.</p>
+ * <br>
+ * @param key key of notification message in langYml
+ * @return Returns the object given or throws an exception
+ * @throws NotificationException exception thrown when null
+ */
+fun <T> T.notifyNull(key: String): T {
+    return this ?: throw NotificationException(key)
+}
+
+/**
+ * Throws an exception containing a langYml key if predicate tests false
+ * <p>The {@link CommandBase#onExecute(CommandSender, List) onExecute } in PluginCommand and Subcommand
+ * automatically handles sending the message to the sender.</p>
+ * <br>
+ * @param predicate predicate to test
+ * @param key       key of notification message in langYml
+ * @param <T>       the generic type of object
+ * @return Returns the object given or throws an exception
+ */
+fun <T> T.notifyFalse(predicate: Predicate<T>, key: String): T {
+    predicate.test(this).notifyFalse(key)
+    return this
+}
+
+/**
+ * Throws an exception containing a langYml key if condition is false.
+ * <p>The {@link CommandBase#onExecute(CommandSender, List) onExecute } in PluginCommand and Subcommand
+ * automatically handles sending the message to the sender.</p>
+ * <br>
+ * @param key       value in the langYml
+ * @return Returns the condition given or throws an exception
+ * @throws NotificationException exception thrown when false
+ */
+fun Boolean?.notifyFalse(key: String): Boolean {
+    return if (this == true) true else throw NotificationException(key)
+}
+
+/**
+ * Throws an exception containing a langYml key if Bukkit.getPlayer(playerName) is null.
+ * <p>The {@link CommandBase#onExecute(CommandSender, List) onExecute } in PluginCommand and Subcommand
+ * automatically handles sending the message to the sender.</p>
+ * <br>
+ * @param key        value in the langYml
+ * @return Returns the player
+ * @throws NotificationException exception thrown when invalid playerName
+ */
+fun String?.notifyPlayerRequired(key: String): Player {
+    return Bukkit.getPlayer(this ?: "") ?: throw NotificationException(key)
+}
+
+/**
+ * Throws an exception containing a langYml key if Bukkit.getPlayer(playerName) is null.
+ * <p>The {@link CommandBase#onExecute(CommandSender, List) onExecute } in PluginCommand and Subcommand
+ * automatically handles sending the message to the sender.</p>
+ * <br>
+ * @param key        value in the langYml
+ * @return Returns the player
+ * @throws NotificationException exception thrown when invalid playerName
+ */
+fun String?.notifyOfflinePlayerRequired(key: String): OfflinePlayer {
+    @Suppress("DEPRECATION")
+    val player = Bukkit.getOfflinePlayer(this ?: "")
+
+    if (!player.hasPlayedBefore() && !player.isOnline) {
+        throw NotificationException(key)
+    }
+
+    return player
+}
+
+/**
+ * Throws an exception containing a langYml key if player doesn't have permission.
+ * <p>The {@link CommandBase#onExecute(CommandSender, List) onExecute } in PluginCommand and Subcommand
+ * automatically handles sending the message to the sender.</p>
+ * <br>
+ * @param permission the permission
+ * @param key        value in the langYml
+ * @return Returns the player
+ * @throws NotificationException exception thrown when player doesn't have permission
+ */
+fun Player?.notifyPermissionRequired(permission: String, key: String): Player {
+    this ?: throw NotificationException(key)
+    return this.notifyFalse({ this.hasPermission(permission) }, key)
+}

eco-api/src/main/kotlin/com/willfp/eco/core/gui/GUIHelpers.kt

@@ -74,12 +74,15 @@ fun SlotBuilder.onClick(clickType: ClickType, action: (Player, InventoryClickEve
 fun SlotBuilder.notCaptiveFor(test: (Player) -> Boolean): SlotBuilder =
     this.notCaptiveFor { test(it) }
 
+/** @see SlotBuilder.setCaptiveFilter */
+fun SlotBuilder.setCaptiveFilter(test: (Player, Menu, ItemStack?) -> Boolean): SlotBuilder =
+    this.setCaptiveFilter { a, b, c -> test(a, b, c) }
+
 /**
  * @see SlotBuilder.setModifier
  * @deprecated Use SlotUpdater instead.
  */
 @Deprecated("Use SlotUpdater instead")
-@Suppress("DEPRECATION")
 fun SlotBuilder.setModifier(action: (Player, Menu, item: ItemStack) -> Unit): SlotBuilder =
     this.setUpdater { a, b, c -> c.apply { action(a, b, c) } }
 

eco-api/src/main/kotlin/com/willfp/eco/core/integrations/shop/ShopHelpers.kt

@@ -2,13 +2,31 @@
 
 package com.willfp.eco.core.integrations.shop
 
+import com.willfp.eco.core.price.Price
 import org.bukkit.entity.Player
 import org.bukkit.inventory.ItemStack
 
 /** @see ShopManager.getItemPrice * */
+@Deprecated(
+    "Prices depend on players, this will always return 0.",
+    level = DeprecationLevel.ERROR,
+    replaceWith = ReplaceWith("this.getValue(player)")
+)
 val ItemStack.price: Double
-    get() = ShopManager.getItemPrice(this)
+    get() = 0.0
 
 /** @see ShopManager.getItemPrice * */
+@Deprecated(
+    "Use the price system instead, prices may not be currencies.",
+    ReplaceWith("this.getValue(player)"),
+)
 fun ItemStack.getPrice(player: Player): Double =
-    ShopManager.getItemPrice(this, player)
+    this.getUnitValue(player).getValue(player, this.amount.toDouble())
+
+/** @see ShopManager.getUnitValue */
+fun ItemStack.getUnitValue(player: Player): Price =
+    ShopManager.getUnitValue(this, player)
+
+/** @see ShopManager.isSellable */
+fun ItemStack?.isSellable(player: Player): Boolean =
+    ShopManager.isSellable(this, player)

eco-api/src/main/kotlin/com/willfp/eco/core/packet/Packet.kt

@@ -0,0 +1,9 @@
+@file:JvmName("PacketExtensions")
+
+package com.willfp.eco.core.packet
+
+import org.bukkit.entity.Player
+
+/** @see Packet.send */
+fun Player.sendPacket(packet: Packet) =
+    packet.send(this)

eco-core/core-backend/src/main/kotlin/com/willfp/eco/internal/command/DelegatedBukkitCommand.kt

@@ -0,0 +1,41 @@
+package com.willfp.eco.internal.command
+
+import org.bukkit.command.Command
+import org.bukkit.command.CommandSender
+import org.bukkit.command.PluginIdentifiableCommand
+import org.bukkit.command.TabCompleter
+
+class DelegatedBukkitCommand(
+    private val delegate: EcoPluginCommand
+) : Command(delegate.name), TabCompleter, PluginIdentifiableCommand {
+    private var _aliases: List<String>? = null
+    private var _description: String? = null
+
+    override fun execute(sender: CommandSender, label: String, args: Array<out String>?): Boolean {
+        return delegate.onCommand(sender, this, label, args)
+    }
+
+    override fun onTabComplete(
+        sender: CommandSender,
+        command: Command,
+        label: String,
+        args: Array<out String>?
+    ): List<String> {
+        return delegate.onTabComplete(sender, this, label, args) ?: emptyList()
+    }
+
+    override fun getPlugin() = delegate.plugin
+    override fun getPermission() = delegate.permission
+    override fun getDescription() = _description ?: delegate.description ?: ""
+    override fun getAliases(): List<String> = _aliases ?: delegate.aliases
+
+    override fun setDescription(description: String): Command {
+        this._description = description
+        return this
+    }
+
+    override fun setAliases(aliases: List<String>): Command {
+        this._aliases = aliases
+        return this
+    }
+}