Added ability to filter items for captive slots

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.
@@ -49,6 +50,17 @@ public abstract class CustomSlot implements Slot {
         return delegate.isCaptive(player, menu);
     }
 
+    @Override
+    public boolean isCaptiveForItem(@NotNull final Player player,
+                             @NotNull final Menu menu,
+                             @Nullable final ItemStack item) {
+        if (delegate == null) {
+            throw new IllegalStateException("Custom Slot was not initialized!");
+        }
+
+        return delegate.isCaptiveForItem(player, menu, item);
+    }
+
     @Override
     public boolean isCaptiveFromEmpty() {
         if (delegate == null) {

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.
@@ -39,6 +40,13 @@ public abstract class ReactiveSlot implements Slot {
         return getSlot(player, menu).isCaptive(player, menu);
     }
 
+    @Override
+    public boolean isCaptiveForItem(@NotNull final Player player,
+                             @NotNull final Menu menu,
+                             @Nullable final ItemStack item) {
+        return getSlot(player, menu).isCaptiveForItem(player, menu, item);
+    }
+
     @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 is captive for this item. (Can this item be placed in it).
+     *
+     * @param player The player.
+     * @param menu   The menu.
+     * @param itemStack The item.
+     * @return If captive.
+     */
+    default boolean isCaptiveForItem(@NotNull final Player player,
+                              @NotNull final Menu menu,
+                              @Nullable final ItemStack itemStack) {
+        return false;
+    }
+
     /**
      * Get the actionable slot to be shown.
      * <p>

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

@@ -6,9 +6,12 @@ import com.willfp.eco.core.gui.slot.functional.SlotUpdater;
 import org.bukkit.entity.Player;
 import org.bukkit.event.inventory.ClickType;
 import org.bukkit.event.inventory.InventoryClickEvent;
+import org.bukkit.inventory.ItemStack;
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
 import java.util.function.BiConsumer;
+import java.util.function.BiPredicate;
 import java.util.function.Predicate;
 
 /**
@@ -143,7 +146,15 @@ 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(Predicate<Player> predicate);
+
+    /**
+     * Prevent captive for players that match a predicate.
+     *
+     * @param predicate The predicate. Returns true when the slot should not be captive.
+     * @return The builder.
+     */
+    SlotBuilder notCaptiveForItem(BiPredicate<Player, @Nullable ItemStack> predicate);
 
     /**
      * Set the ItemStack updater.

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

@@ -74,6 +74,10 @@ fun SlotBuilder.onClick(clickType: ClickType, action: (Player, InventoryClickEve
 fun SlotBuilder.notCaptiveFor(test: (Player) -> Boolean): SlotBuilder =
     this.notCaptiveFor { test(it) }
 
+/** @see SlotBuilder.notCaptiveFor */
+fun SlotBuilder.notCaptiveForItem(test: (Player, ItemStack?) -> Boolean): SlotBuilder =
+    this.notCaptiveForItem { player, item -> test(player, item) }
+
 /**
  * @see SlotBuilder.setModifier
  * @deprecated Use SlotUpdater instead.