From d82b5b0a49ae6f72dd7d3889eca92c0869e8150e 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 c38295a0..43c491f7 100644
--- a/src/main/java/net/minecraft/server/MobSpawnerAbstract.java
+++ b/src/main/java/net/minecraft/server/MobSpawnerAbstract.java
@@ -105,6 +105,27 @@ 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.a(((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 02157d05..224443e0 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) {
@@ -77,6 +77,25 @@ public final class SpawnerCreature {
                                                     if (a(entitypositiontypes_surface, (IWorldReader) worldserver, (BlockPosition) blockposition_mutableblockposition, entitytypes) && EntityPositionTypes.a(entitytypes, worldserver, EnumMobSpawn.NATURAL, blockposition_mutableblockposition, worldserver.random) && worldserver.a(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(worldserver, blockposition_mutableblockposition),
+                                                            type, SpawnReason.NATURAL
+                                                        );
+                                                        if (!event.callEvent()) {
+                                                            if (event.shouldAbortSpawn()) {
+                                                                return;
+                                                            }
+                                                            ++i2;
+                                                            continue;
+                                                        }
+                                                    }
+                                                    // Paper end
+
                                                         try {
                                                             Entity entity = entitytypes.a((World) worldserver);
 
-- 
2.25.1.windows.1