Keep track of opened merchant inventory

Author: booky10

src/main/java/dev/booky/craftattack/shops/ShopListener.java

@@ -10,6 +10,7 @@
 import io.papermc.paper.event.player.PlayerTradeEvent;
 import io.papermc.paper.event.player.PrePlayerAttackEntityEvent;
 import io.papermc.paper.event.server.ServerResourcesReloadedEvent;
+import net.kyori.adventure.util.Ticks;
 import org.bukkit.Bukkit;
 import org.bukkit.GameMode;
 import org.bukkit.Location;
@@ -33,6 +34,7 @@
 import org.bukkit.util.Vector;
 import org.jspecify.annotations.NullMarked;
 
+import java.lang.ref.WeakReference;
 import java.util.HashSet;
 import java.util.Iterator;
 import java.util.Set;
@@ -51,6 +53,8 @@ public final class ShopListener implements Listener {
     private final LoadingCache<AbstractVillager, ShopVillager> villagerCache;
     private final Set<ShopVillager> villagerSaveQueue = new HashSet<>();
 
+    private final Set<MerchantEntry> openedMerchants = new HashSet<>();
+
     public ShopListener(CaManager manager) {
         this.manager = manager;
         this.shopKey = new NamespacedKey(manager.getPlugin(), "shop");
@@ -161,8 +165,7 @@ public void onEntityInteract(PlayerInteractEntityEvent event) {
         Player player = event.getPlayer();
 
         if (!player.isSneaking()) {
-            boolean opened = ShopMenu.openMerchantMenu(this.manager.getPlugin(), shop, player);
-            if (!opened) {
+            if (!this.openTradeInventory(shop, player)) {
                 player.sendMessage(CaManager.getPrefix().append(translatable("ca.menu.shop.no-trades")));
                 if (shop.isOwner(player)) {
                     player.sendMessage(CaManager.getPrefix().append(translatable("ca.menu.shop.no-trades.owner-hit")));
@@ -219,13 +222,23 @@ public void onPlayerTrade(PlayerTradeEvent event) {
                 if (!(event.getPlayer().getOpenInventory() instanceof MerchantView)) {
                     return; // exited merchant inventory menu
                 }
-                if (!ShopMenu.openMerchantMenu(this.manager.getPlugin(), shop, event.getPlayer())) {
+                if (!this.openTradeInventory(shop, event.getPlayer())) {
                     event.getPlayer().closeInventory(); // no trades present
                 }
             });
         }
     }
 
+    public boolean openTradeInventory(ShopVillager shop, Player player) {
+        AbstractVillager merchant = ShopMenu.openMerchantMenu(this.manager.getPlugin(), shop, player);
+        if (merchant == null) {
+            return false; // failed
+        }
+        // keep track of opened merchants
+        this.openedMerchants.add(new MerchantEntry(shop, player, merchant));
+        return true;
+    }
+
     @EventHandler
     public void onTickEnd(ServerTickEndEvent event) {
         // players may bulk-buy a few items, so we have a queue for saving shop villager data to prevent lags
@@ -239,5 +252,50 @@ public void onTickEnd(ServerTickEndEvent event) {
                 }
             }
         }
+        this.openedMerchants.removeIf(MerchantEntry::tick);
+    }
+
+    private static class MerchantEntry {
+
+        private static final int TTL = Ticks.TICKS_PER_SECOND * 60 * 5; // 5 minutes
+
+        private final ShopVillager shop;
+        private final WeakReference<Player> player;
+        private final WeakReference<AbstractVillager> merchant;
+
+        private int ttl = TTL;
+
+        public MerchantEntry(ShopVillager shop, Player player, AbstractVillager merchant) {
+            this.shop = shop;
+            this.player = new WeakReference<>(player);
+            this.merchant = new WeakReference<>(merchant);
+        }
+
+        public boolean checkValid() {
+            Player player = this.player.get();
+            if (player == null || !player.isValid() || !player.isConnected()) {
+                return false; // player has left/died
+            }
+            AbstractVillager merchant = this.merchant.get();
+            if (merchant == null || !merchant.isValid()) {
+                return false; // opened merchant has become invalid
+            } else if (this.ttl < 1) {
+                return false; // expired
+            }
+            this.shop.ensureLoaded(); // check original shop villager
+            return true;
+        }
+
+        public boolean tick() {
+            if (!this.checkValid()) {
+                Player player = this.player.get();
+                if (player != null && player.getOpenInventory() instanceof MerchantView) {
+                    player.closeInventory();
+                }
+                return true; // removed
+            }
+            this.ttl--;
+            return false;
+        }
     }
 }

src/main/java/dev/booky/craftattack/shops/ShopMenu.java

@@ -17,7 +17,6 @@
 import net.kyori.adventure.key.Key;
 import net.kyori.adventure.sound.Sound;
 import net.kyori.adventure.text.Component;
-import net.kyori.adventure.util.Ticks;
 import org.bukkit.Keyed;
 import org.bukkit.Material;
 import org.bukkit.NamespacedKey;
@@ -61,7 +60,6 @@ public final class ShopMenu {
     private static final int TRADES_PER_PAGE = 4;
     private static final int MAX_TRADES = 20;
     public static final Material EMPTY_INGREDIENT = Material.STRUCTURE_VOID;
-    private static final int PER_PLAYER_TRADER_TTL = Ticks.TICKS_PER_SECOND * 60 * 5;
 
     private static final Map<Villager.Type, Material> VILL_TYPE_ITEMS = Map.ofEntries(
             Map.entry(Villager.Type.DESERT, Material.SAND),
@@ -125,10 +123,10 @@ public static List<MerchantRecipe> buildRecipes(ShopVillager shop) {
         return filtered;
     }
 
-    public static boolean openMerchantMenu(Plugin plugin, ShopVillager shop, Player player) {
+    public static @Nullable AbstractVillager openMerchantMenu(Plugin plugin, ShopVillager shop, Player player) {
         List<MerchantRecipe> recipes = buildRecipes(shop);
         if (recipes.isEmpty()) {
-            return false; // no recipes available
+            return null; // no recipes available
         }
         // spawn separate merchant per player to allow multiple players to access one shop at the same time
         AbstractVillager merchant = shop.getMerchant();
@@ -138,7 +136,8 @@ public static boolean openMerchantMenu(Plugin plugin, ShopVillager shop, Player
             trader.setSilent(true);
             trader.setVisibleByDefault(false);
             trader.setCollidable(false);
-            trader.setDespawnDelay(PER_PLAYER_TRADER_TTL);
+            // instantly despawn after player has closed the inventory
+            trader.setDespawnDelay(1);
             trader.setRecipes(recipes);
 
             NamespacedKey refKey = new NamespacedKey(plugin, "shop/reference");
@@ -150,7 +149,7 @@ public static boolean openMerchantMenu(Plugin plugin, ShopVillager shop, Player
                 .checkReachable(true)
                 .title(translatable("ca.menu.shop.merchant"))
                 .build(player).open();
-        return true; // report success!
+        return spawnedMerchant; // report success!
     }
 
     public static void openMenu(ShopVillager shop, Player player) {