Add InventoryMoveItemEvent. Adds BUKKIT-3765

This event is being called whenever a block or entity (e.g. hopper) tries to
move an item from one inventory to another inventory (one inventory may be
the hopper itself).

By: Dennis Bliefernicht <dennis.bliefernicht@triphoenix.de>

paper-api/src/main/java/org/bukkit/event/inventory/InventoryMoveItemEvent.java

@@ -0,0 +1,109 @@
+package org.bukkit.event.inventory;
+
+import org.apache.commons.lang.Validate;
+import org.bukkit.event.Cancellable;
+import org.bukkit.event.Event;
+import org.bukkit.event.HandlerList;
+import org.bukkit.inventory.Inventory;
+import org.bukkit.inventory.ItemStack;
+
+/**
+ * Called when some entity or block (e.g. hopper) tries to move items
+ * directly from one inventory to another.
+ *
+ * When this event is called, the initiator may already have removed the item
+ * from the source inventory and is ready to move it into the destination
+ * inventory.
+ *
+ * If this event is cancelled, the items will be returned to the source
+ * inventory, if needed.
+ *
+ * If this event is not cancelled, the initiator will try to put the
+ * ItemStack into the destination inventory. If this is not possible and the
+ * ItemStack has not been modified, the source inventory slot will be
+ * restored to its former state. Otherwise any additional items will be
+ * discarded.
+ */
+public class InventoryMoveItemEvent extends Event implements Cancellable {
+    private static final HandlerList handlers = new HandlerList();
+    private boolean cancelled;
+    private final Inventory sourceInventory;
+    private final Inventory destinationInventory;
+    private ItemStack itemStack;
+    private final boolean didSourceInitiate;
+
+    public InventoryMoveItemEvent(final Inventory sourceInventory, final ItemStack itemStack, final Inventory destinationInventory, final boolean didSourceInitiate) {
+        Validate.notNull(itemStack, "ItemStack cannot be null");
+        this.sourceInventory = sourceInventory;
+        this.itemStack = itemStack;
+        this.destinationInventory = destinationInventory;
+        this.didSourceInitiate = didSourceInitiate;
+    }
+
+    /**
+     * Gets the Inventory that the ItemStack is being taken from
+     *
+     * @return Inventory that the ItemStack is being taken from
+     */
+    public Inventory getSource() {
+        return sourceInventory;
+    }
+
+    /**
+     * Gets the ItemStack being moved; if modified, the original item will
+     * not be removed from the source inventory.
+     *
+     * @return ItemStack
+     */
+    public ItemStack getItem() {
+        return itemStack.clone();
+    }
+
+    /**
+     * Sets the ItemStack being moved; if this is different from the original
+     * ItemStack, the original item will not be removed from the source
+     * inventory.
+     *
+     * @param itemStack The ItemStack
+     */
+    public void setItem(ItemStack itemStack) {
+        Validate.notNull(itemStack, "ItemStack cannot be null.  Cancel the event if you want nothing to be transferred.");
+        this.itemStack = itemStack.clone();
+    }
+
+    /**
+     * Gets the Inventory that the ItemStack is being put into
+     *
+     * @return Inventory that the ItemStack is being put into
+     */
+    public Inventory getDestination() {
+        return destinationInventory;
+    }
+
+    /**
+     * Gets the Inventory that initiated the transfer.  This will always
+     * be either the destination or source Inventory.
+     *
+     * @return Inventory that initiated the transfer
+     */
+    public Inventory getInitiator() {
+        return didSourceInitiate ? sourceInventory : destinationInventory;
+    }
+
+    public boolean isCancelled() {
+        return cancelled;
+    }
+
+    public void setCancelled(boolean cancel) {
+        this.cancelled = cancel;
+    }
+
+    @Override
+    public HandlerList getHandlers() {
+        return handlers;
+    }
+
+    public static HandlerList getHandlerList() {
+        return handlers;
+    }
+}