Fix slime/magma cube replication

src/main/java/com/songoda/ultimatestacker/listeners/entity/EntityCurrentListener.java

@@ -3,11 +3,18 @@ package com.songoda.ultimatestacker.listeners.entity;
 import com.songoda.ultimatestacker.UltimateStacker;
 import com.songoda.ultimatestacker.stackable.entity.EntityStack;
 import com.songoda.ultimatestacker.stackable.entity.EntityStackManager;
+import org.bukkit.Bukkit;
+import org.bukkit.entity.Entity;
 import org.bukkit.entity.LivingEntity;
+import org.bukkit.entity.Slime;
 import org.bukkit.event.EventHandler;
 import org.bukkit.event.EventPriority;
 import org.bukkit.event.Listener;
 import org.bukkit.event.entity.EntityTransformEvent;
+import org.bukkit.event.world.EntitiesLoadEvent;
+
+import java.util.Arrays;
+import java.util.List;
 
 public class EntityCurrentListener implements Listener {
 
@@ -23,6 +30,11 @@ public class EntityCurrentListener implements Listener {
         if (stackManager.isStackedEntity(event.getEntity())
                 && event.getEntity() instanceof LivingEntity
                 && event.getTransformedEntity() instanceof LivingEntity) {
+            if (event.getTransformReason().equals(EntityTransformEvent.TransformReason.SPLIT)) {
+                stackManager.getStack((LivingEntity) event.getEntity()).removeEntityFromStack(1);
+                event.setCancelled(true);
+                return;
+            }
             EntityStack stack = stackManager.updateStack((LivingEntity) event.getEntity(), (LivingEntity) event.getTransformedEntity());
             stack.releaseHost();
         }

src/main/java/com/songoda/ultimatestacker/stackable/entity/EntityStack.java

@@ -53,7 +53,7 @@ public class EntityStack extends StackedEntity {
         return hostEntity;
     }
 
-    protected void setHostEntity(LivingEntity hostEntity) {
+    protected synchronized void setHostEntity(LivingEntity hostEntity) {
         this.hostEntity = hostEntity;
     }
 
@@ -89,7 +89,6 @@ public class EntityStack extends StackedEntity {
 
     private void handleSingleStackDeath(LivingEntity killed, List<Drop> drops, int droppedExp, EntityDeathEvent event) {
         EntityStackManager stackManager = plugin.getEntityStackManager();
-
         Bukkit.getPluginManager().callEvent(new EntityStackKillEvent(this, false));
 
         Vector velocity = killed.getVelocity().clone();
@@ -138,16 +137,16 @@ public class EntityStack extends StackedEntity {
         }
     }
 
-    public LivingEntity takeOneAndSpawnEntity(Location location) {
+    public synchronized LivingEntity takeOneAndSpawnEntity(Location location) {
         if (amount <= 0) return null;
-        amount--;
         LivingEntity entity = Objects.requireNonNull(location.getWorld()).spawn(location, hostEntity.getClass());
         this.hostEntity = entity;
+        setAmount(amount--);
         updateNameTag();
         return entity;
     }
 
-    public void releaseHost() {
+    public synchronized void releaseHost() {
         LivingEntity oldHost = hostEntity;
         LivingEntity entity = takeOneAndSpawnEntity(hostEntity.getLocation());
         if (getAmount() >= 0) {
@@ -158,7 +157,7 @@ public class EntityStack extends StackedEntity {
         }
     }
 
-    public void destroy() {
+    public synchronized void destroy() {
         if (hostEntity == null) return;
         Bukkit.getScheduler().runTask(plugin, hostEntity::remove);
         hostEntity = null;

src/main/java/com/songoda/ultimatestacker/stackable/entity/EntityStackManager.java

@@ -89,10 +89,25 @@ public class EntityStackManager {
         return stack;
     }
 
+    /**
+     * Transfers the stack from one entity to another.
+     * (e.g. slimes split)
+     * @param oldEntity The old entity to transfer the stack from.
+     * @param newEntity The new entity to transfer the stack to.
+     * @return The new stack.
+     */
+    public EntityStack transferStack(LivingEntity oldEntity, LivingEntity newEntity) {
+        EntityStack stack = getStack(oldEntity);
+        if (stack == null) return null;
+        EntityStack newStack = new EntityStack(newEntity, stack.getAmount());
+        stack.destroy();
+        return newStack;
+    }
+
     public EntityStack updateStack(LivingEntity oldEntity, LivingEntity newEntity) {
         EntityStack stack = getStack(oldEntity);
         if (stack == null) return null;
-        int amount = stack.getAmount();
+        int amount = stack.getAmount()-1;
         stack.destroy();
         return createStack(newEntity, amount);
     }
@@ -101,7 +116,6 @@ public class EntityStackManager {
         if (isStackedEntity(newEntity)) {
             EntityStack stack = getStack(newEntity);
             stack.setAmount(amount);
-            System.err.println("Stacked entity already exists, updating stack amount to " + amount);
         } else {
             createStack(newEntity, amount);
         }

src/main/java/com/songoda/ultimatestacker/tasks/StackingTask.java

@@ -65,7 +65,7 @@ import java.util.concurrent.ScheduledExecutorService;
 public class StackingTask implements Runnable {
 
     private final UltimateStacker plugin;
-    private final ScheduledExecutorService executorService = Executors.newScheduledThreadPool(4);
+    private final ScheduledExecutorService executorService = Executors.newSingleThreadScheduledExecutor();
 
     private final EntityStackManager stackManager;
 
@@ -93,7 +93,6 @@ public class StackingTask implements Runnable {
     public StackingTask(UltimateStacker plugin) {
         this.plugin = plugin;
         this.stackManager = plugin.getEntityStackManager();
-
         // Add loaded worlds.
         for (World world : Bukkit.getWorlds())
             loadedWorlds.add(new SWorld(world));