Added onOpen to menu

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

@@ -68,6 +68,14 @@ public interface MenuBuilder {
      */
     MenuBuilder onClose(@NotNull CloseHandler action);
 
+    /**
+     * Set the menu open handler.
+     *
+     * @param action The handler.
+     * @return The builder.
+     */
+    MenuBuilder onOpen(@NotNull OpenHandler action);
+
     /**
      * Set the action to run on render.
      *

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

@@ -0,0 +1,19 @@
+package com.willfp.eco.core.gui.menu;
+
+import org.bukkit.entity.Player;
+import org.jetbrains.annotations.NotNull;
+
+/**
+ * Interface to run on menu open.
+ */
+@FunctionalInterface
+public interface OpenHandler {
+    /**
+     * Performs this operation on the given arguments.
+     *
+     * @param player The player.
+     * @param menu   The menu.
+     */
+    void handle(@NotNull Player player,
+                @NotNull Menu menu);
+}

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

@@ -109,6 +109,10 @@ fun slot(
 fun MenuBuilder.onClose(action: (InventoryCloseEvent, Menu) -> Unit): MenuBuilder =
     this.onClose { a, b -> action(a, b) }
 
+/** @see MenuBuilder.onOpen */
+fun MenuBuilder.onOpen(action: (Player, Menu) -> Unit): MenuBuilder =
+    this.onOpen { a, b -> action(a, b) }
+
 /** @see MenuBuilder.modify */
 fun MenuBuilder.modify(modifier: (MenuBuilder) -> Unit): MenuBuilder =
     this.modfiy { modifier(it) }