Add new LivingConversionEvent to control mobs turning into other mobs. (#7386)

src/main/java/net/minecraftforge/event/ForgeEventFactory.java

@@ -21,6 +21,7 @@ package net.minecraftforge.event;
 
 import java.io.File;
 import java.util.*;
+import java.util.function.Consumer;
 
 import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
@@ -36,6 +37,7 @@ import net.minecraft.command.Commands;
 import net.minecraft.entity.Entity;
 import net.minecraft.entity.Pose;
 import net.minecraft.entity.EntitySize;
+import net.minecraft.entity.EntityType;
 import net.minecraft.entity.MobEntity;
 import net.minecraft.entity.SpawnReason;
 import net.minecraft.entity.LivingEntity;
@@ -103,6 +105,7 @@ import net.minecraftforge.event.entity.PlaySoundAtEntityEvent;
 import net.minecraftforge.event.entity.ProjectileImpactEvent;
 import net.minecraftforge.event.entity.item.ItemExpireEvent;
 import net.minecraftforge.event.entity.living.AnimalTameEvent;
+import net.minecraftforge.event.entity.living.LivingConversionEvent;
 import net.minecraftforge.event.entity.living.LivingDestroyBlockEvent;
 import net.minecraftforge.event.entity.living.LivingEntityUseItemEvent;
 import net.minecraftforge.event.entity.living.LivingExperienceDropEvent;
@@ -748,4 +751,14 @@ public class ForgeEventFactory
         MinecraftForge.EVENT_BUS.post(evt);
         return evt;
     }
+
+    public static boolean canLivingConvert(LivingEntity entity, EntityType<? extends LivingEntity> outcome, Consumer<Integer> timer)
+    {
+        return !MinecraftForge.EVENT_BUS.post(new LivingConversionEvent.Pre(entity, outcome, timer));
+    }
+
+    public static void onLivingConvert(LivingEntity entity, LivingEntity outcome)
+    {
+        MinecraftForge.EVENT_BUS.post(new LivingConversionEvent.Post(entity, outcome));
+    }
 }

src/main/java/net/minecraftforge/event/entity/living/LivingConversionEvent.java

@@ -0,0 +1,108 @@
+/*
+ * Minecraft Forge
+ * Copyright (c) 2016-2020.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation version 2.1
+ * of the License.
+ *
+ * This library 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
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ */
+
+package net.minecraftforge.event.entity.living;
+
+import net.minecraft.entity.EntityType;
+import net.minecraft.entity.LivingEntity;
+import net.minecraftforge.eventbus.api.Cancelable;
+
+import java.util.function.Consumer;
+
+public class LivingConversionEvent extends LivingEvent
+{
+    public LivingConversionEvent(LivingEntity entity)
+    {
+        super(entity);
+    }
+
+    /**
+     * LivingConversionEvent.Pre is triggered when an entity is trying
+     * to replace itself with another entity
+     *
+     * This event may trigger every tick even if it was cancelled last tick
+     * for entities like Zombies and Hoglins. To prevent it, the conversion
+     * timer needs to be changed or reset
+     *
+     * This event is {@link Cancelable}
+     * If cancelled, the replacement will not occur
+     */
+    @Cancelable
+    public static class Pre extends LivingConversionEvent
+    {
+        private final EntityType<? extends LivingEntity> outcome;
+        private final Consumer<Integer> timer;
+
+        public Pre(LivingEntity entity, EntityType<? extends LivingEntity> outcome, Consumer<Integer> timer)
+        {
+            super(entity);
+            this.outcome = outcome;
+            this.timer = timer;
+        }
+
+        /**
+         * Gets the entity type of the new entity this living entity is
+         * converting to
+         * @return the entity type of the new entity
+         */
+        public EntityType<? extends LivingEntity> getOutcome()
+        {
+            return outcome;
+        }
+
+        /**
+         * Sets the conversion timer, by changing this it prevents the
+         * event being triggered every tick
+         * Do note the timer of some of the entities are increments, but
+         * some of them are decrements
+         * Not every conversion is applicable for this
+         * @param ticks timer ticks
+         */
+        public void setConversionTimer(int ticks)
+        {
+            timer.accept(ticks);
+        }
+    }
+
+    /**
+     * LivingConversionEvent.Post is triggered when an entity is replacing
+     * itself with another entity.
+     * The old living entity is likely to be removed right after this event.
+     */
+    public static class Post extends LivingConversionEvent
+    {
+        private final LivingEntity outcome;
+
+        public Post(LivingEntity entity, LivingEntity outcome)
+        {
+            super(entity);
+            this.outcome = outcome;
+        }
+
+        /**
+         * Gets the finalized new entity (with all data like potion
+         * effect and equipments set)
+         * @return the finalized new entity
+         */
+        public LivingEntity getOutcome()
+        {
+            return outcome;
+        }
+    }
+}