InventoryGui allows item duplication in GUIs which use GuiStorageElement

@@ -22,6 +22,7 @@
  * SOFTWARE.
  */
 
+import org.bukkit.Bukkit;
 import org.bukkit.ChatColor;
 import org.bukkit.Material;
 import org.bukkit.entity.HumanEntity;
@@ -40,6 +41,8 @@
  * accessed by the player then it will translate to the second slot in the inventory.
  */
 public class GuiStorageElement extends GuiElement {
+    private final static String STORAGE_SYSTEM_PROPERTY = GuiStorageElement.class.getName() + ".forceAllow";
+
     private final Inventory storage;
     private final int invSlot;
     private Runnable applyStorage;
@@ -54,7 +57,7 @@ public class GuiStorageElement extends GuiElement {
     public GuiStorageElement(char slotChar, Inventory storage) {
         this(slotChar, storage, -1);
     }
-    
+
     /**
      * An element used to access a specific slot in an {@link Inventory}.
      * @param slotChar  The character to replace in the gui setup string.
@@ -64,7 +67,7 @@ public GuiStorageElement(char slotChar, Inventory storage) {
     public GuiStorageElement(char slotChar, Inventory storage, int invSlot) {
         this(slotChar, storage, invSlot, null, null);
     }
-    
+
     /**
      * An element used to access a specific slot in an {@link Inventory}.
      * @param slotChar      The character to replace in the gui setup string.
@@ -91,6 +94,11 @@ public GuiStorageElement(char slotChar, Inventory storage, int invSlot, Runnable
      */
     public GuiStorageElement(char slotChar, Inventory storage, int invSlot, Runnable applyStorage, Function<ValidatorInfo, Boolean> placeValidator, Function<ValidatorInfo, Boolean> takeValidator) {
         super(slotChar, null);
+        if (Bukkit.getUnsafe().getDataVersion() < 4554 && !Boolean.getBoolean(STORAGE_SYSTEM_PROPERTY)) {
+            throw new UnsupportedOperationException("GuiStorageElements require server version 1.21.9 or later to work properly!"
+                    + " If you understand the risk and only want to use this element for internal use you can disable this check"
+                    + " by setting the system property " + STORAGE_SYSTEM_PROPERTY + "=true");
+        }
         this.invSlot = invSlot;
         this.applyStorage = applyStorage;
         this.placeValidator = placeValidator;
@@ -99,15 +107,24 @@ public GuiStorageElement(char slotChar, Inventory storage, int invSlot, Runnable
             if (getStorageSlot(click.getWhoClicked(), click.getSlot()) < 0) {
                 return true;
             }
+            ItemStack storageItem = getStorageItem(click.getWhoClicked(), click.getSlot());
             ItemStack slotItem = GuiView.of(click.getRawEvent().getView()).getTopInventory().getItem(click.getSlot());
 
             if (click.getType() == ClickType.RIGHT && (
                     click.getCursor() != null && click.getCursor().getType().getKey().getKey().contains("bundle")
+                            || storageItem != null && storageItem.getType().getKey().getKey().contains("bundle")
                             || slotItem != null && slotItem.getType().getKey().getKey().contains("bundle"))) {
                 gui.draw(click.getWhoClicked(), false);
                 return true;
             }
 
+            if (slotItem == null && storageItem != null && storageItem.getType() != Material.AIR
+                    || storageItem == null && slotItem != null && slotItem.getType() != Material.AIR
+                    || storageItem != null && !storageItem.equals(slotItem)) {
+                gui.draw(click.getWhoClicked(), false);
+                return true;
+            }
+
             if (!(click.getRawEvent() instanceof InventoryClickEvent)) {
                 // Only the click event will be handled here, drag event is handled separately
                 return true;
@@ -245,14 +262,18 @@ public GuiStorageElement(char slotChar, Inventory storage, int invSlot, Runnable
                     click.getRawEvent().getWhoClicked().sendMessage(ChatColor.RED + "The action " + event.getAction() + " is not supported! Sorry about that :(");
                     return true;
             }
-            return !validateItemPlace(click.getWhoClicked(), click.getSlot(), movedItem);
+            return !setStorageItem(click.getWhoClicked(), click.getSlot(), movedItem);
         });
         this.storage = storage;
     }
 
     @Override
     public ItemStack getItem(HumanEntity who, int slot) {
-        return getStorageItem(who, slot);
+        int index = getStorageSlot(who, slot);
+        if (index > -1 && index < storage.getSize()) {
+            return storage.getItem(index);
+        }
+        return null;
     }
 
     /**
@@ -262,7 +283,7 @@ public ItemStack getItem(HumanEntity who, int slot) {
     public Inventory getStorage() {
         return storage;
     }
-    
+
     /**
      * Get the storage slot index that corresponds to the InventoryGui slot
      * @param player    The player which is using the GUI view
@@ -276,7 +297,7 @@ private int getStorageSlot(HumanEntity player, int slot) {
         }
         return index;
     }
-    
+
     /**
      * Get the item in the storage that corresponds to the InventoryGui slot
      * @param slot      The slot in the GUI
@@ -301,7 +322,7 @@ public ItemStack getStorageItem(HumanEntity player, int slot) {
         }
         return null;
     }
-    
+
     /**
      * Set the item in the storage that corresponds to the InventoryGui slot.
      * @param slot  The slot in the GUI
@@ -335,15 +356,15 @@ public boolean setStorageItem(HumanEntity player, int slot, ItemStack item) {
         }
         return true;
     }
-    
+
     /**
      * Get the runnable that applies the storage
      * @return The storage applying runnable; might be null
      */
     public Runnable getApplyStorage() {
         return applyStorage;
     }
-    
+
     /**
      * Set what should be done to apply the storage.
      * Not necessary if the storage is directly backed by a real inventory.
@@ -352,7 +373,7 @@ public Runnable getApplyStorage() {
     public void setApplyStorage(Runnable applyStorage) {
         this.applyStorage = applyStorage;
     }
-    
+
     /**
      * Get the item place validator
      * @return The item place validator
@@ -378,7 +399,7 @@ public Function<ValidatorInfo, Boolean> getPlaceValidator() {
     public Function<ValidatorInfo, Boolean> getTakeValidator() {
         return takeValidator;
     }
-    
+
     /**
      * Set a function that can validate whether an item can be placed in the slot
      * @param placeValidator The item validator that takes a {@link ValidatorInfo} and returns <code>true</code> for items that
@@ -407,7 +428,7 @@ public void setPlaceValidator(Function<ValidatorInfo, Boolean> placeValidator) {
     public void setTakeValidator(Function<ValidatorInfo, Boolean> takeValidator) {
         this.takeValidator = takeValidator;
     }
-    
+
     /**
      * Validate whether an item can be placed in a slot with the item validator set in {@link #setItemValidator(Function)}
      * @param slot  The slot the item should be tested for
@@ -455,21 +476,21 @@ public static class ValidatorInfo {
         private final GuiElement element;
         private final int slot;
         private final ItemStack item;
-    
+
         public ValidatorInfo(GuiElement element, int slot, ItemStack item) {
             this.item = item;
             this.slot = slot;
             this.element = element;
         }
-    
+
         public GuiElement getElement() {
             return element;
         }
-    
+
         public int getSlot() {
             return slot;
         }
-    
+
         public ItemStack getItem() {
             return item;
         }

@@ -527,12 +527,8 @@ public void setPageNumber(int pageNumber) {
      * @param pageNumber    The page number to set
      */
     public void setPageNumber(HumanEntity player, int pageNumber) {
-        Inventory inventory = getInventory(player);
-        if (inventory != null) {
-            storeItems(player, inventory);
-        }
         setPageNumberInternal(player, pageNumber);
-        draw(player, false, false, false);
+        draw(player, false, false);
     }
 
     private void setPageNumberInternal(HumanEntity player, int pageNumber) {
@@ -684,18 +680,11 @@ public void draw(HumanEntity who, boolean updateDynamic) {
      * @param recreateInventory Recreate the inventory
      */
     public void draw(HumanEntity who, boolean updateDynamic, boolean recreateInventory) {
-        draw(who, updateDynamic, recreateInventory, true);
-    }
-
-    private void draw(HumanEntity who, boolean updateDynamic, boolean recreateInventory, boolean storeItems) {
         if (updateDynamic) {
             updateElements(who, elements.values());
         }
         calculatePageAmount(who);
         Inventory inventory = getInventory(who);
-        if (storeItems && inventory != null) {
-            storeItems(who, inventory);
-        }
         if (inventory == null || recreateInventory) {
             build();
             if (slots.length != inventoryType.getDefaultSize()) {
@@ -718,19 +707,6 @@ private void draw(HumanEntity who, boolean updateDynamic, boolean recreateInvent
         }
     }
 
-    private void storeItems(HumanEntity who, Inventory inventory) {
-        for (int i = 0; i < inventory.getSize(); i++) {
-            GuiElement element = getElement(i);
-            if (element != null) {
-                GuiElement effectiveElement = element.getEffectiveElement(who, i);
-                if (effectiveElement instanceof GuiStorageElement) {
-                    GuiStorageElement storageElement = (GuiStorageElement) effectiveElement;
-                    storageElement.setStorageItem(who, i, inventory.getItem(i));
-                }
-            }
-        }
-    }
-
     /**
      * Schedule a task on a {@link HumanEntity}/main thread to run on the next tick
      * @param entity the human entity to schedule a task on
@@ -1393,7 +1369,7 @@ public void onInventoryDrag(InventoryDragEvent event) {
                     if (items.getKey() < inventory.getSize()) {
                         GuiElement element = getElement(items.getKey());
                         if (!(element instanceof GuiStorageElement)
-                                || !((GuiStorageElement) element).validateItemPlace(event.getWhoClicked(), items.getKey(), items.getValue())) {
+                                || !((GuiStorageElement) element).setStorageItem(event.getWhoClicked(), items.getKey(), items.getValue())) {
                             ItemStack slotItem = event.getInventory().getItem(items.getKey());
                             if (!items.getValue().isSimilar(slotItem)) {
                                 rest += items.getValue().getAmount();
@@ -1440,7 +1416,6 @@ public void onInventoryDrag(InventoryDragEvent event) {
         public void onInventoryClose(InventoryCloseEvent event) {
             Inventory inventory = getInventory(event.getPlayer());
             if (event.getInventory().equals(inventory)) {
-                storeItems(event.getPlayer(), inventory);
                 // go back. that checks if the player is in gui and has history
                 if (InventoryGui.this.equals(getOpen(event.getPlayer()))) {
                     if (closeAction == null || closeAction.onClose(new Close(event.getPlayer(), InventoryGui.this, event))) {