From 5ec4e4eb79464575a464f37d17f6c282708019d9 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Sun, 14 Jan 2018 17:01:31 -0500
Subject: [PATCH] PreCreatureSpawnEvent

Adds an event to fire before an Entity is created, so that plugins that need to cancel
CreatureSpawnEvent can do so from this event instead.

Cancelling CreatureSpawnEvent rapidly causes a lot of garbage collection and CPU waste
as it's done after the Entity object has been fully created.

Mob Limiting plugins and blanket "ban this type of monster" plugins should use this event
instead and save a lot of server resources.

See: https://github.com/PaperMC/Paper/issues/917

diff --git a/src/main/java/net/minecraft/server/MobSpawnerAbstract.java b/src/main/java/net/minecraft/server/MobSpawnerAbstract.java
index 59bd9ccd70..6f5d8b0315 100644
--- a/src/main/java/net/minecraft/server/MobSpawnerAbstract.java
+++ b/src/main/java/net/minecraft/server/MobSpawnerAbstract.java
@@ -104,6 +104,28 @@ public abstract class MobSpawnerAbstract {
                     double d5 = j >= 3 ? nbttaglist.h(2) : (double) blockposition.getZ() + (world.random.nextDouble() - world.random.nextDouble()) * (double) this.spawnRange + 0.5D;
 
                     if (world.c(((EntityTypes) optional.get()).a(d3, d4, d5)) && EntityPositionTypes.a((EntityTypes) optional.get(), world.getMinecraftWorld(), EnumMobSpawn.SPAWNER, new BlockPosition(d3, d4, d5), world.getRandom())) {
+                    // Paper start
+                    EntityTypes entityType = optional.get();
+                    String key = EntityTypes.getName(entityType).getKey();
+
+                    org.bukkit.entity.EntityType type = org.bukkit.entity.EntityType.fromName(key);
+                    if (type != null) {
+                        com.destroystokyo.paper.event.entity.PreCreatureSpawnEvent event;
+                        event = new com.destroystokyo.paper.event.entity.PreCreatureSpawnEvent(
+                            MCUtil.toLocation(world, d3, d4, d5),
+                            type,
+                            org.bukkit.event.entity.CreatureSpawnEvent.SpawnReason.SPAWNER
+                        );
+                        if (!event.callEvent()) {
+                            flag = true;
+                            if (event.shouldAbortSpawn()) {
+                                break;
+                            }
+                            continue;
+                        }
+                    }
+                    // Paper end
+
                         Entity entity = EntityTypes.a(nbttagcompound, world, (entity1) -> {
                             entity1.setPositionRotation(d3, d4, d5, entity1.yaw, entity1.pitch);
                             return entity1;
diff --git a/src/main/java/net/minecraft/server/SpawnerCreature.java b/src/main/java/net/minecraft/server/SpawnerCreature.java
index 4aa65c1934..4458b48ee8 100644
--- a/src/main/java/net/minecraft/server/SpawnerCreature.java
+++ b/src/main/java/net/minecraft/server/SpawnerCreature.java
@@ -38,7 +38,7 @@ public final class SpawnerCreature {
                     BiomeBase.BiomeMeta biomebase_biomemeta = null;
                     GroupDataEntity groupdataentity = null;
                     int l1 = MathHelper.f(Math.random() * 4.0D);
-                    int i2 = 0;
+                    int i2 = 0; // Paper - force diff on name change
                     int j2 = 0;
 
                     while (true) {
@@ -74,6 +74,25 @@ public final class SpawnerCreature {
                                                 if (a(entitypositiontypes_surface, (IWorldReader) world, (BlockPosition) blockposition_mutableblockposition, entitytypes) && EntityPositionTypes.a(entitytypes, world, EnumMobSpawn.NATURAL, blockposition_mutableblockposition, world.random) && world.c(entitytypes.a((double) f, (double) k, (double) f1))) {
                                                     EntityInsentient entityinsentient;
 
+                                                    // Paper start
+                                                    com.destroystokyo.paper.event.entity.PreCreatureSpawnEvent event;
+                                                    EntityTypes<?> cls = biomebase_biomemeta.b;
+                                                    org.bukkit.entity.EntityType type = org.bukkit.entity.EntityType.fromName(EntityTypes.getName(cls).getKey());
+                                                    if (type != null) {
+                                                        event = new com.destroystokyo.paper.event.entity.PreCreatureSpawnEvent(
+                                                            MCUtil.toLocation(world, blockposition_mutableblockposition),
+                                                            type, SpawnReason.NATURAL
+                                                        );
+                                                        if (!event.callEvent()) {
+                                                            if (event.shouldAbortSpawn()) {
+                                                                return;
+                                                            }
+                                                            ++i2;
+                                                            continue;
+                                                        }
+                                                    }
+                                                    // Paper end
+
                                                     try {
                                                         Entity entity = entitytypes.a(world);
 
-- 
2.22.0