From fb131c12346a5af919527a31c38f5b67d3ee450d Mon Sep 17 00:00:00 2001
From: Florian Fabre <florian.fabre@ikmail.com>
Date: Sat, 10 Oct 2026 19:50:35 +0200
Subject: [PATCH] fix: prevent backpack upgrade ingredient duplication

Intercept custom backpack upgrade result clicks and manually consume one
ingredient from each surrounding crafting slot. This prevents stacked
upgrade materials from being duplicated because dynamically generated
backpack results do not match the UUID-based registered recipe result.
---
 .../listeners/BackpackCraftingListener.java   | 101 +++++++++++++++++-
 1 file changed, 97 insertions(+), 4 deletions(-)

diff --git a/src/main/java/com/shweit/expendablebackpacks/listeners/BackpackCraftingListener.java b/src/main/java/com/shweit/expendablebackpacks/listeners/BackpackCraftingListener.java
index 32e42f0..a60573b 100644
--- a/src/main/java/com/shweit/expendablebackpacks/listeners/BackpackCraftingListener.java
+++ b/src/main/java/com/shweit/expendablebackpacks/listeners/BackpackCraftingListener.java
@@ -3,15 +3,14 @@
 import com.shweit.expendablebackpacks.items.BackpackItem;
 import com.shweit.expendablebackpacks.items.BackpackTier;
 import com.shweit.expendablebackpacks.storage.BackpackManager;
-import java.util.UUID;
-import org.bukkit.Bukkit;
+import java.util.Objects;
 import org.bukkit.Material;
 import org.bukkit.entity.Player;
 import org.bukkit.event.EventHandler;
 import org.bukkit.event.EventPriority;
 import org.bukkit.event.Listener;
-import org.bukkit.event.inventory.ClickType;
-import org.bukkit.event.inventory.CraftItemEvent;
+import org.bukkit.event.inventory.InventoryClickEvent;
+import org.bukkit.event.inventory.InventoryType;
 import org.bukkit.event.inventory.PrepareItemCraftEvent;
 import org.bukkit.inventory.CraftingInventory;
 import org.bukkit.inventory.ItemStack;
@@ -143,6 +142,100 @@ public void onCraft(PrepareItemCraftEvent event) {
         }
     }
 
+    /**
+     * Handles clicks on the result slot for backpack upgrades.
+     *
+     * <p>Upgrade results are dynamically created in PrepareItemCraftEvent. The registered
+     * recipe result uses a dummy backpack with a different UUID, so the normal Bukkit
+     * transaction cannot reliably consume stacked ingredients.</p>
+     *
+     * @param event the inventory click event
+     */
+    @EventHandler(priority = EventPriority.HIGH)
+    public void onInventoryClick(InventoryClickEvent event) {
+        if (event.getSlotType() != InventoryType.SlotType.RESULT
+            || !(event.getInventory() instanceof CraftingInventory)) {
+            return;
+        }
+
+        CraftingInventory inventory = (CraftingInventory) event.getInventory();
+        ItemStack[] matrix = Objects.requireNonNull(inventory.getMatrix(),
+            "Crafting inventory returned a null matrix");
+        ItemStack result = inventory.getResult();
+
+        if (matrix.length != 9
+            || result == null
+            || !BackpackItem.isBackpack(result)
+            || !isUpgradePattern(matrix)) {
+            return;
+        }
+
+        Player player = (Player) event.getWhoClicked();
+        if (!event.getClick().isShiftClick()
+            && player.getItemOnCursor().getType() != Material.AIR) {
+            return;
+        }
+
+        event.setCancelled(true);
+
+        if (event.getClick().isShiftClick()) {
+            player.getInventory().addItem(result.clone());
+        } else {
+            player.setItemOnCursor(result.clone());
+        }
+
+        consumeUpgradeIngredients(inventory, matrix);
+    }
+
+    /**
+     * Checks whether the matrix contains a valid backpack upgrade.
+     *
+     * @param matrix the crafting matrix
+     * @return true if the matrix is a valid upgrade
+     */
+    private boolean isUpgradePattern(ItemStack[] matrix) {
+        if (!BackpackItem.isBackpack(matrix[4])) {
+            return false;
+        }
+
+        BackpackTier currentTier = BackpackItem.getBackpackTier(matrix[4]);
+        Material surrounding = getSurroundingMaterial(matrix);
+        if (currentTier == null || surrounding == null) {
+            return false;
+        }
+
+        return (surrounding == Material.DIRT && currentTier == BackpackTier.LEATHER)
+            || (surrounding == Material.COPPER_INGOT && currentTier == BackpackTier.LEATHER)
+            || (surrounding == Material.IRON_INGOT && currentTier == BackpackTier.COPPER)
+            || (surrounding == Material.GOLD_INGOT && currentTier == BackpackTier.IRON)
+            || (surrounding == Material.DIAMOND && currentTier == BackpackTier.GOLD);
+    }
+
+    /**
+     * Consumes one backpack and one item from each surrounding slot.
+     *
+     * @param inventory the crafting inventory
+     * @param matrix the current crafting matrix
+     */
+    private void consumeUpgradeIngredients(CraftingInventory inventory, ItemStack[] matrix) {
+        int[] surrounding = {0, 1, 2, 3, 5, 6, 7, 8};
+        for (int index : surrounding) {
+            ItemStack ingredient = matrix[index];
+            if (ingredient == null || ingredient.getType() == Material.AIR) {
+                continue;
+            }
+            if (ingredient.getAmount() == 1) {
+                matrix[index] = null;
+            } else {
+                ItemStack remaining = ingredient.clone();
+                remaining.setAmount(ingredient.getAmount() - 1);
+                matrix[index] = remaining;
+            }
+        }
+        matrix[4] = null;
+        inventory.setMatrix(matrix);
+    }
+
     /**
      * Check if the pattern matches Leather Backpack crafting.
      * L S L