Implement a way to override the prediction of start slot for inventory at shiftclick

src/main/java/net/minestom/server/inventory/AbstractInventory.java

@@ -1,5 +1,6 @@
 package net.minestom.server.inventory;
 
+import net.minestom.server.entity.Player;
 import net.minestom.server.event.EventDispatcher;
 import net.minestom.server.event.inventory.InventoryItemChangeEvent;
 import net.minestom.server.event.inventory.PlayerInventoryItemChangeEvent;
@@ -56,6 +57,33 @@ public synchronized void setItemStack(int slot, @NotNull ItemStack itemStack) {
         safeItemInsert(slot, itemStack);
     }
 
+
+    // Microtus - fix shift click for inventory
+    /**
+     * Gets the slot for a shift click operation.
+     * <p>
+     * This is used to determine where the item should be placed when shift clicking.
+     *
+     * @param index the slot index
+     * @return the slot where the item should be placed when shift clicking
+     */
+    int getStartSlotForShiftClick(int index, Player player) {
+        return 0;
+    }
+
+    /**
+     * Gets the slot for a double click operation.
+     * <p>
+     * This is used to determine where the item should be placed when double-clicking.
+     *
+     * @param index the slot index
+     * @return the slot where the item should be placed when double-clicking
+     */
+    int getStartSlotForDoubleClick(int index, Player player) {
+        return 0;
+    }
+    // Microtus - fix shift click for inventory
+
     /**
      * Inserts safely an item into the inventory.
      * <p>

src/main/java/net/minestom/server/inventory/Inventory.java

@@ -246,7 +246,7 @@ public boolean shiftClick(@NotNull Player player, int slot, int button) { // Mic
         final InventoryClickResult clickResult = clickProcessor.shiftClick(
                 isInWindow ? this : playerInventory,
                 isInWindow ? playerInventory : this,
-                0, isInWindow ? playerInventory.getInnerSize() : getInnerSize(), 1,
+                getStartSlotForShiftClick(clickSlot, player), isInWindow ? playerInventory.getInnerSize() : getInnerSize(), 1, // Microtus - fix shift click for inventory
                 player, clickSlot, clicked, cursor, button); // Microtus
         if (clickResult.isCancel()) {
             updateAll(player);
@@ -262,6 +262,29 @@ public boolean shiftClick(@NotNull Player player, int slot, int button) { // Mic
         return true;
     }
 
+    // Microtus - fix shift click for inventory
+    @Override
+    int getStartSlotForShiftClick(int index, Player player) {
+        if (index == 0) {
+            return 9;
+        }
+        if (index >= 1 && index < 5) {
+            return 9;
+        }
+        // TODO: Add armor slot support
+        if (index >= 5 && index < 9) {
+            return 9;
+        }
+        if (index >= 9 && index < 36) {
+            return 36;
+        }
+        if (index >= 36 && index < 45) {
+            return 9;
+        }
+        return 9;
+    }
+    // Microtus - fix shift click for inventory
+
     @Override
     public boolean changeHeld(@NotNull Player player, int slot, int key) {
         final int convertedKey = key == 40 ? PlayerInventoryUtils.OFFHAND_SLOT : key;
@@ -352,7 +375,7 @@ public boolean doubleClick(@NotNull Player player, int slot) {
                 ItemStack.AIR;
         final ItemStack cursor = playerInventory.getCursorItem();
         final InventoryClickResult clickResult = clickProcessor.doubleClick(isInWindow ? this : playerInventory,
-                this, player, clickSlot, clicked, cursor);
+                this, player, clickSlot, clicked, cursor, getStartSlotForDoubleClick(slot, player)); // Microtus - fix shift click for inventory
         if (clickResult.isCancel()) {
             updateAll(player);
             return false;

src/main/java/net/minestom/server/inventory/PlayerInventory.java

@@ -273,7 +273,8 @@ public boolean doubleClick(@NotNull Player player, int slot) {
         final int convertedSlot = convertPlayerInventorySlot(slot, OFFSET);
         final ItemStack cursor = getCursorItem();
         final ItemStack clicked = getItemStack(convertedSlot);
-        final InventoryClickResult clickResult = clickProcessor.doubleClick(this, this, player, convertedSlot, clicked, cursor);
+        final InventoryClickResult clickResult = clickProcessor.doubleClick(this, this, player, convertedSlot, clicked, cursor, getStartSlotForDoubleClick(slot, player));
+         // Microtus - fix shift click for inventory
         if (clickResult.isCancel()) {
             update();
             return false;

src/main/java/net/minestom/server/inventory/click/InventoryClickProcessor.java

@@ -289,7 +289,7 @@ public final class InventoryClickProcessor {
     }
 
     public @NotNull InventoryClickResult doubleClick(@NotNull AbstractInventory clickedInventory, @NotNull AbstractInventory inventory, @NotNull Player player, int slot,
-                                                     @NotNull ItemStack clicked, @NotNull ItemStack cursor) {
+                                                     @NotNull ItemStack clicked, @NotNull ItemStack cursor, int startSlot) { // Microtus - fix shift click for inventory
         InventoryClickResult clickResult = startCondition(player, clickedInventory, slot, ClickType.START_DOUBLE_CLICK, clicked, cursor);
         if (clickResult.isCancel()) return clickResult;
         if (cursor.isAir()) return clickResult.cancelled();
@@ -307,7 +307,7 @@ public final class InventoryClickProcessor {
                     return false;
                 final InventoryClickResult result = startCondition(player, inv, index, ClickType.DOUBLE_CLICK, itemStack, cursor);
                 return !result.isCancel();
-            });
+            }, startSlot, inventory.getInnerSize(), 1); // Microtus - fix shift click for inventory
             final ItemStack itemResult = pair.left();
             var itemChangesMap = pair.right();
             itemChangesMap.forEach((Integer s, ItemStack itemStack) -> {