Fix item delete in own inventory

Dragging items across top and bottom inventories with own inventory open resulted in the overlapping content being deleted.

plugin/src/main/java/com/lishid/openinv/OpenInv.java

@@ -150,6 +150,20 @@ public class OpenInv extends JavaPlugin implements IOpenInv {
         }
     }
 
+    /**
+     * Convert a raw slot number into a player inventory slot number.
+     *
+     * <p>Note that this method is specifically for converting an ISpecialPlayerInventory slot number into a regular
+     * player inventory slot number.
+     *
+     * @param view the open inventory view
+     * @param rawSlot the raw slot in the view
+     * @return the converted slot number
+     */
+    public int convertToPlayerSlot(InventoryView view, int rawSlot) {
+        return this.accessor.getPlayerDataManager().convertToPlayerSlot(view, rawSlot);
+    }
+
     @Override
     public boolean disableSaving() {
         return this.getConfig().getBoolean("settings.disable-saving", false);

plugin/src/main/java/com/lishid/openinv/internal/IPlayerDataManager.java

@@ -54,6 +54,18 @@ public interface IPlayerDataManager {
     @Nullable
     InventoryView openInventory(@NotNull Player player, @NotNull ISpecialInventory inventory);
 
+    /**
+     * Convert a raw slot number into a player inventory slot number.
+     *
+     * <p>Note that this method is specifically for converting an ISpecialPlayerInventory slot number into a regular
+     * player inventory slot number.
+     *
+     * @param view the open inventory view
+     * @param rawSlot the raw slot in the view
+     * @return the converted slot number
+     */
+    int convertToPlayerSlot(InventoryView view, int rawSlot);
+
     void sendSystemMessage(@NotNull Player player, @NotNull String message);
 
     @NotNull

plugin/src/main/java/com/lishid/openinv/internal/OpenInventoryView.java

@@ -0,0 +1,83 @@
+/*
+ * Copyright (C) 2011-2021 lishid. All rights reserved.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.lishid.openinv.internal;
+
+import com.lishid.openinv.OpenInv;
+import org.bukkit.entity.HumanEntity;
+import org.bukkit.entity.Player;
+import org.bukkit.event.inventory.InventoryType;
+import org.bukkit.inventory.Inventory;
+import org.bukkit.inventory.InventoryView;
+import org.jetbrains.annotations.NotNull;
+
+public class OpenInventoryView extends InventoryView {
+
+    private final Player player;
+    private final ISpecialInventory inventory;
+    private final String titleKey;
+    private final String titleDefaultSuffix;
+    private String title;
+
+    public OpenInventoryView(Player player, ISpecialInventory inventory, String titleKey, String titleDefaultSuffix) {
+        this.player = player;
+        this.inventory = inventory;
+        this.titleKey = titleKey;
+        this.titleDefaultSuffix = titleDefaultSuffix;
+    }
+
+    @Override
+    public @NotNull Inventory getTopInventory() {
+        return inventory.getBukkitInventory();
+    }
+
+    @Override
+    public @NotNull Inventory getBottomInventory() {
+        return getPlayer().getInventory();
+    }
+
+    @Override
+    public @NotNull HumanEntity getPlayer() {
+        return player;
+    }
+
+    @Override
+    public @NotNull InventoryType getType() {
+        return inventory.getBukkitInventory().getType();
+    }
+
+    @Override
+    public @NotNull String getTitle() {
+        if (title == null) {
+            HumanEntity owner = getPlayer();
+
+            String localTitle = OpenInv.getPlugin(OpenInv.class)
+                    .getLocalizedMessage(
+                            owner,
+                            titleKey,
+                            "%player%",
+                            owner.getName());
+            if (localTitle != null) {
+                title = localTitle;
+            } else  {
+                title = owner.getName() + titleDefaultSuffix;
+            }
+        }
+
+        return title;
+    }
+
+}

plugin/src/main/java/com/lishid/openinv/listeners/InventoryListener.java

@@ -20,6 +20,9 @@ import com.lishid.openinv.OpenInv;
 import com.lishid.openinv.internal.ISpecialPlayerInventory;
 import com.lishid.openinv.util.InventoryAccess;
 import com.lishid.openinv.util.Permissions;
+import java.util.Map;
+import java.util.Set;
+import java.util.stream.Collectors;
 import org.bukkit.GameMode;
 import org.bukkit.entity.HumanEntity;
 import org.bukkit.entity.Player;
@@ -32,8 +35,10 @@ import org.bukkit.event.inventory.InventoryCloseEvent;
 import org.bukkit.event.inventory.InventoryDragEvent;
 import org.bukkit.event.inventory.InventoryInteractEvent;
 import org.bukkit.inventory.Inventory;
+import org.bukkit.inventory.InventoryView;
 import org.bukkit.inventory.ItemStack;
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
 /**
  * Listener for inventory-related events to prevent modification of inventories where not allowed.
@@ -67,11 +72,6 @@ public class InventoryListener implements Listener {
             return;
         }
 
-        // Only specially handle actions in the player's own inventory.
-        if (!event.getWhoClicked().equals(event.getView().getTopInventory().getHolder())) {
-            return;
-        }
-
         // Safe cast - has to be a player to be the holder of a special player inventory.
         Player player = (Player) event.getWhoClicked();
 
@@ -102,14 +102,65 @@ public class InventoryListener implements Listener {
 
     @EventHandler(priority = EventPriority.LOWEST)
     public void onInventoryDrag(@NotNull final InventoryDragEvent event) {
-        handleInventoryInteract(event);
+        if (handleInventoryInteract(event)) {
+            return;
+        }
+
+        InventoryView view = event.getView();
+        int topSize = view.getTopInventory().getSize();
+
+        // Get bottom inventory active slots as player inventory slots.
+        Set<Integer> slots = event.getRawSlots().stream()
+                .filter(slot -> slot >= topSize)
+                .map(slot -> plugin.convertToPlayerSlot(view, slot)).collect(Collectors.toSet());
+
+        int overlapLosses = 0;
+
+        // Count overlapping slots.
+        for (Map.Entry<Integer, ItemStack> newItem : event.getNewItems().entrySet()) {
+            int rawSlot = newItem.getKey();
+
+            // Skip bottom inventory slots.
+            if (rawSlot >= topSize) {
+                continue;
+            }
+
+            int convertedSlot = plugin.convertToPlayerSlot(view, rawSlot);
+
+            if (slots.contains(convertedSlot)) {
+                overlapLosses += getCountDiff(view.getItem(rawSlot), newItem.getValue());
+            }
+        }
+
+        // Allow no overlap to proceed as usual.
+        if (overlapLosses < 1) {
+            return;
+        }
+
+        ItemStack cursor = event.getCursor();
+        if (cursor != null) {
+            cursor.setAmount(cursor.getAmount() + overlapLosses);
+        } else {
+            cursor = event.getOldCursor().clone();
+            cursor.setAmount(overlapLosses);
+        }
+
+        event.setCursor(cursor);
+    }
+
+    private int getCountDiff(@Nullable ItemStack original, @NotNull ItemStack result) {
+        if (original == null || original.getType() != result.getType()) {
+            return result.getAmount();
+        }
+
+        return result.getAmount() - original.getAmount();
     }
 
     /**
      * Handle common InventoryInteractEvent functions.
      *
      * @param event the InventoryInteractEvent
-     * @return true unless the top inventory is an opened player inventory
+     * @return true unless the top inventory is the holder's own inventory
      */
     private boolean handleInventoryInteract(@NotNull final InventoryInteractEvent event) {
         HumanEntity entity = event.getWhoClicked();
@@ -147,7 +198,8 @@ public class InventoryListener implements Listener {
             return true;
         }
 
-        return false;
+        // Only specially handle actions in the player's own inventory.
+        return !event.getWhoClicked().equals(event.getView().getTopInventory().getHolder());
     }
 
 }