SPIGOT-336, SPIGOT-3366, SPIGOT-5768, SPIGOT-6409, SPIGOT-6861, #722: Add EntityRemoveEvent

By: DerFrZocker <derrieple@gmail.com>

paper-api/src/main/java/org/bukkit/event/entity/EntityRemoveEvent.java

@@ -0,0 +1,116 @@
+package org.bukkit.event.entity;
+
+import org.bukkit.entity.Entity;
+import org.bukkit.event.HandlerList;
+import org.jetbrains.annotations.ApiStatus;
+import org.jetbrains.annotations.NotNull;
+
+/**
+ * Called when an {@link Entity} is removed.
+ * <p>
+ * This event should only be used for monitoring. The result
+ * of modifying the entity during or after this event is unspecified.
+ * This event is not called for a {@link org.bukkit.entity.Player}.
+ */
+@ApiStatus.Experimental
+public class EntityRemoveEvent extends EntityEvent {
+
+    private static final HandlerList handlers = new HandlerList();
+    private final Cause cause;
+
+    public EntityRemoveEvent(@NotNull Entity what, @NotNull Cause cause) {
+        super(what);
+        this.cause = cause;
+    }
+
+    /**
+     * Gets the cause why the entity got removed.
+     *
+     * @return the cause why the entity got removed
+     */
+    @NotNull
+    public Cause getCause() {
+        return cause;
+    }
+
+    @NotNull
+    @Override
+    public HandlerList getHandlers() {
+        return handlers;
+    }
+
+    @NotNull
+    public static HandlerList getHandlerList() {
+        return handlers;
+    }
+
+    /**
+     * Represents various ways an entity gets removed.
+     */
+    public enum Cause {
+        /**
+         * When an entity dies.
+         */
+        DEATH,
+        /**
+         * When an entity does despawn. This includes mobs which are too far away,
+         * items or arrows which lay to long on the ground or area effect cloud.
+         */
+        DESPAWN,
+        /**
+         * When an entity gets removed because it drops as an item.
+         * For example, trident or falling sand.
+         * <p>
+         * <b>Note:</b> Depending on other factors, such as gamerules, no item will actually drop,
+         * the cause, however, will still be drop.
+         */
+        DROP,
+        /**
+         * When an entity gets removed because it enters a block.
+         * For example, bees or silverfish.
+         */
+        ENTER_BLOCK,
+        /**
+         * When an entity gets removed because it exploded.
+         * For example, creepers, tnt or firework.
+         */
+        EXPLODE,
+        /**
+         * When an entity gets removed because it hit something. This mainly applies to projectiles.
+         */
+        HIT,
+        /**
+         * When an entity gets removed because it merges with another one.
+         * For example, items or xp.
+         */
+        MERGE,
+        /**
+         * When an entity gets removed because it is too far below the world.
+         * This only applies to entities which get removed immediately,
+         * some entities get damage instead.
+         */
+        OUT_OF_WORLD,
+        /**
+         * When an entity gets removed because it got pickup.
+         * For example, items, arrows, xp or parrots which get on a player shoulder.
+         */
+        PICKUP,
+        /**
+         * When an entity gets removed with a player because the player quits the game.
+         * For example, a boat which gets removed with the player when he quits.
+         */
+        PLAYER_QUIT,
+        /**
+         * When a plugin manually removes an entity.
+         */
+        PLUGIN,
+        /**
+         * When an entity gets removed because it transforms into another one.
+         */
+        TRANSFORMATION,
+        /**
+         * When the chunk an entity is in gets unloaded.
+         */
+        UNLOAD,
+    }
+}