Prevent dragging items outside of invsee (#5902)

Fixes #3065

---------

Co-authored-by: JRoy <10731363+JRoy@users.noreply.github.com>

Author: tanyaofei

Essentials/src/main/java/com/earth2me/essentials/EssentialsPlayerListener.java

@@ -43,6 +43,7 @@
 import org.bukkit.event.inventory.ClickType;
 import org.bukkit.event.inventory.InventoryClickEvent;
 import org.bukkit.event.inventory.InventoryCloseEvent;
+import org.bukkit.event.inventory.InventoryDragEvent;
 import org.bukkit.event.inventory.InventoryType;
 import org.bukkit.event.player.AsyncPlayerChatEvent;
 import org.bukkit.event.player.PlayerBucketEmptyEvent;
@@ -995,6 +996,26 @@ private boolean isPreventBindingHat(User user, PlayerInventory inventory) {
         return false;
     }
 
+    @EventHandler(priority = EventPriority.LOWEST, ignoreCancelled = true)
+    public void onInventoryDragEvent(final InventoryDragEvent event) {
+        final InventoryViewProvider provider = ess.provider(InventoryViewProvider.class);
+        final Inventory top = provider.getTopInventory(event.getView());
+        if (top.getType() != InventoryType.PLAYER) {
+            return;
+        }
+        final User user = ess.getUser((Player) event.getWhoClicked());
+        if (!user.isInvSee()) {
+            return;
+        }
+
+        for (int slot : event.getNewItems().keySet()) {
+            if (Inventories.isBottomInventorySlot(slot)) {
+                event.setCancelled(true);
+                break;
+            }
+        }
+    }
+
     @EventHandler(priority = EventPriority.MONITOR)
     public void onInventoryCloseEvent(final InventoryCloseEvent event) {
         Player refreshPlayer = null;

Essentials/src/main/java/com/earth2me/essentials/craftbukkit/Inventories.java

@@ -424,4 +424,8 @@ public static boolean isContortedSlot(final int slot) {
     private static boolean isArmorSlot(final int slot) {
         return slot == HELM_SLOT || slot == CHEST_SLOT || slot == LEG_SLOT || slot == BOOT_SLOT;
     }
+
+    public static boolean isBottomInventorySlot(final int slot) {
+        return slot > 35;
+    }
 }