From 0000000000000000000000000000000000000000 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 efd4d2844c4ad638837a1fd971927758908e7db1..45cd44335427a818a580158d57025289f37079bf 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.b(((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 e08de74543535072e63ecfc9bd3ada95c9dbfeb7..137fa3e51390e95f5939f2251e0d170accbfb469 100644
--- a/src/main/java/net/minecraft/server/SpawnerCreature.java
+++ b/src/main/java/net/minecraft/server/SpawnerCreature.java
@@ -185,7 +185,12 @@ public final class SpawnerCreature {
                                         j1 = biomebase_biomemeta.d + worldserver.random.nextInt(1 + biomebase_biomemeta.e - biomebase_biomemeta.d);
                                     }
 
-                                    if (a(worldserver, enumcreaturetype, structuremanager, chunkgenerator, biomebase_biomemeta, blockposition_mutableblockposition, d2) && spawnercreature_c.test(biomebase_biomemeta.c, blockposition_mutableblockposition, ichunkaccess)) {
+                                    // Paper start
+                                    Boolean doSpawning = a(worldserver, enumcreaturetype, structuremanager, chunkgenerator, biomebase_biomemeta, blockposition_mutableblockposition, d2);
+                                    if (doSpawning == null) {
+                                        return;
+                                    }
+                                    if (doSpawning.booleanValue() && spawnercreature_c.test(biomebase_biomemeta.c, blockposition_mutableblockposition, ichunkaccess)) { // Paper end
                                         EntityInsentient entityinsentient = a(worldserver, biomebase_biomemeta.c);
 
                                         if (entityinsentient == null) {
@@ -239,8 +244,24 @@ public final class SpawnerCreature {
         }
     }
 
-    private static boolean a(WorldServer worldserver, EnumCreatureType enumcreaturetype, StructureManager structuremanager, ChunkGenerator chunkgenerator, BiomeBase.BiomeMeta biomebase_biomemeta, BlockPosition.MutableBlockPosition blockposition_mutableblockposition, double d0) {
+    private static Boolean a(WorldServer worldserver, EnumCreatureType enumcreaturetype, StructureManager structuremanager, ChunkGenerator chunkgenerator, BiomeBase.BiomeMeta biomebase_biomemeta, BlockPosition.MutableBlockPosition blockposition_mutableblockposition, double d0) { // Paper
         EntityTypes<?> entitytypes = biomebase_biomemeta.c;
+        // Paper start
+        com.destroystokyo.paper.event.entity.PreCreatureSpawnEvent event;
+        org.bukkit.entity.EntityType type = org.bukkit.entity.EntityType.fromName(EntityTypes.getName(entitytypes).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 null;
+                }
+                return false; // TODO is this handled correctly?
+            }
+        }
+        // Paper end
 
         if (entitytypes.e() == EnumCreatureType.MISC) {
             return false;