From 85440e9c1108aa2da61d7e8b3e9d1844b00a0b7d 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 93fad14d3..55764deec 100644
--- a/src/main/java/net/minecraft/server/MobSpawnerAbstract.java
+++ b/src/main/java/net/minecraft/server/MobSpawnerAbstract.java
@@ -103,6 +103,27 @@ public abstract class MobSpawnerAbstract {
                     double d4 = j >= 2 ? nbttaglist.h(1) : (double) (blockposition.getY() + world.random.nextInt(3) - 1);
                     double d5 = j >= 3 ? nbttaglist.h(2) : (double) blockposition.getZ() + (world.random.nextDouble() - world.random.nextDouble()) * (double) this.spawnRange + 0.5D;
 
+                    // Paper start
+                    EntityTypes entityType = optional.get();
+                    String key = entityType.getKey().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
+
                     if (world.c(((EntityTypes) optional.get()).a(d3, d4, d5))) {
                         Entity entity = EntityTypes.a(nbttagcompound, world, (entity1) -> {
                             entity1.setPositionRotation(d3, d4, d5, entity1.yaw, entity1.pitch);
diff --git a/src/main/java/net/minecraft/server/SpawnerCreature.java b/src/main/java/net/minecraft/server/SpawnerCreature.java
index f4f842b86..d25c7231d 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 (entitypositiontypes_surface != null && a(entitypositiontypes_surface, (IWorldReader) world, (BlockPosition) blockposition_mutableblockposition, entitytypes) && 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);
 
-- 
2.21.0