--- a/net/minecraft/server/WorldServer.java
+++ b/net/minecraft/server/WorldServer.java
@@ -34,6 +34,15 @@
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 
+// CraftBukkit start
+import org.bukkit.Bukkit;
+import org.bukkit.WeatherType;
+import org.bukkit.craftbukkit.event.CraftEventFactory;
+import org.bukkit.event.entity.CreatureSpawnEvent;
+import org.bukkit.event.server.MapInitializeEvent;
+import org.bukkit.event.weather.LightningStrikeEvent;
+// CraftBukkit end
+
 public class WorldServer extends World {
 
     private static final Logger LOGGER = LogManager.getLogger();
@@ -58,12 +67,29 @@
     @Nullable
     private final MobSpawnerTrader mobSpawnerTrader;
 
-    public WorldServer(MinecraftServer minecraftserver, Executor executor, WorldNBTStorage worldnbtstorage, WorldData worlddata, DimensionManager dimensionmanager, GameProfilerFiller gameprofilerfiller, WorldLoadListener worldloadlistener) {
+    // CraftBukkit start
+    private int tickPosition;
+
+    // Add env and gen to constructor
+    public WorldServer(MinecraftServer minecraftserver, Executor executor, WorldNBTStorage worldnbtstorage, WorldData worlddata, DimensionManager dimensionmanager, GameProfilerFiller gameprofilerfiller, WorldLoadListener worldloadlistener, org.bukkit.World.Environment env, org.bukkit.generator.ChunkGenerator gen) {
         super(worlddata, dimensionmanager, (world, worldprovider) -> {
-            return new ChunkProviderServer((WorldServer) world, worldnbtstorage.getDirectory(), worldnbtstorage.getDataFixer(), worldnbtstorage.f(), executor, worldprovider.getChunkGenerator(), minecraftserver.getPlayerList().getViewDistance(), worldloadlistener, () -> {
+            // CraftBukkit start
+            ChunkGenerator<?> chunkGenerator;
+
+            if (gen != null) {
+                chunkGenerator = new org.bukkit.craftbukkit.generator.CustomChunkGenerator(world, world.getSeed(), gen);
+            } else {
+                chunkGenerator = worldprovider.getChunkGenerator();
+            }
+
+            return new ChunkProviderServer((WorldServer) world, worldnbtstorage.getDirectory(), worldnbtstorage.getDataFixer(), worldnbtstorage.f(), executor, chunkGenerator, minecraftserver.getPlayerList().getViewDistance(), worldloadlistener, () -> {
                 return minecraftserver.getWorldServer(DimensionManager.OVERWORLD).getWorldPersistentData();
             });
-        }, gameprofilerfiller, false);
+            // CraftBukkit end
+        }, gameprofilerfiller, false, gen, env);
+        this.pvpMode = minecraftserver.getPVP();
+        worlddata.world = this;
+        // CraftBukkit end
         this.nextTickListBlock = new TickListServer<>(this, (block) -> {
             return block == null || block.getBlockData().isAir();
         }, IRegistry.BLOCK::getKey, IRegistry.BLOCK::get, this::b);
@@ -85,7 +111,8 @@
             this.getWorldData().setGameType(minecraftserver.getGamemode());
         }
 
-        this.mobSpawnerTrader = this.worldProvider.getDimensionManager() == DimensionManager.OVERWORLD ? new MobSpawnerTrader(this) : null;
+        this.mobSpawnerTrader = this.worldProvider.getDimensionManager().getType() == DimensionManager.OVERWORLD ? new MobSpawnerTrader(this) : null; // CraftBukkit - getType()
+        this.getServer().addWorld(this.getWorld()); // CraftBukkit
     }
 
     public void doTick(BooleanSupplier booleansupplier) {
@@ -162,6 +189,7 @@
             this.rainLevel = MathHelper.a(this.rainLevel, 0.0F, 1.0F);
         }
 
+        /* CraftBukkit start
         if (this.lastRainLevel != this.rainLevel) {
             this.server.getPlayerList().a((Packet) (new PacketPlayOutGameStateChange(7, this.rainLevel)), this.worldProvider.getDimensionManager());
         }
@@ -180,13 +208,34 @@
             this.server.getPlayerList().sendAll(new PacketPlayOutGameStateChange(7, this.rainLevel));
             this.server.getPlayerList().sendAll(new PacketPlayOutGameStateChange(8, this.thunderLevel));
         }
+        // */
+        for (int idx = 0; idx < this.players.size(); ++idx) {
+            if (((EntityPlayer) this.players.get(idx)).world == this) {
+                ((EntityPlayer) this.players.get(idx)).tickWeather();
+            }
+        }
+
+        if (flag != this.isRaining()) {
+            // Only send weather packets to those affected
+            for (int idx = 0; idx < this.players.size(); ++idx) {
+                if (((EntityPlayer) this.players.get(idx)).world == this) {
+                    ((EntityPlayer) this.players.get(idx)).setPlayerWeather((!flag ? WeatherType.DOWNFALL : WeatherType.CLEAR), false);
+                }
+            }
+        }
+        for (int idx = 0; idx < this.players.size(); ++idx) {
+            if (((EntityPlayer) this.players.get(idx)).world == this) {
+                ((EntityPlayer) this.players.get(idx)).updateWeather(this.lastRainLevel, this.rainLevel, this.lastThunderLevel, this.thunderLevel);
+            }
+        }
+        // CraftBukkit end
 
         if (this.getWorldData().isHardcore() && this.getDifficulty() != EnumDifficulty.HARD) {
             this.getWorldData().setDifficulty(EnumDifficulty.HARD);
         }
 
         if (this.C && this.players.stream().noneMatch((entityplayer) -> {
-            return !entityplayer.isSpectator() && !entityplayer.isDeeplySleeping();
+            return !entityplayer.isSpectator() && !entityplayer.isDeeplySleeping() && !entityplayer.fauxSleeping; // CraftBukkit
         })) {
             this.C = false;
             if (this.getGameRules().getBoolean(GameRules.DO_DAYLIGHT_CYCLE)) {
@@ -225,7 +274,7 @@
         this.ae();
         this.ticking = false;
         gameprofilerfiller.exitEnter("entities");
-        boolean flag3 = !this.players.isEmpty() || !this.getForceLoadedChunks().isEmpty();
+        boolean flag3 = true || !this.players.isEmpty() || !this.getForceLoadedChunks().isEmpty(); // CraftBukkit - this prevents entity cleanup, other issues on servers with no players
 
         if (flag3) {
             this.resetEmptyTime();
@@ -239,6 +288,11 @@
 
             for (i = 0; i < this.globalEntityList.size(); ++i) {
                 entity = (Entity) this.globalEntityList.get(i);
+                // CraftBukkit start - Fixed an NPE
+                if (entity == null) {
+                    continue;
+                }
+                // CraftBukkit end
                 this.a((entity1) -> {
                     ++entity1.ticksLived;
                     entity1.tick();
@@ -257,6 +311,7 @@
                 Entity entity1 = (Entity) entry.getValue();
                 Entity entity2 = entity1.getVehicle();
 
+                /* CraftBukkit start - We prevent spawning in general, so this butchering is not needed
                 if (!this.server.getSpawnAnimals() && (entity1 instanceof EntityAnimal || entity1 instanceof EntityWaterAnimal)) {
                     entity1.die();
                 }
@@ -264,6 +319,7 @@
                 if (!this.server.getSpawnNPCs() && entity1 instanceof NPC) {
                     entity1.die();
                 }
+                // CraftBukkit end */
 
                 if (entity2 != null) {
                     if (!entity2.dead && entity2.w(entity1)) {
@@ -324,10 +380,10 @@
                     entityhorseskeleton.r(true);
                     entityhorseskeleton.setAgeRaw(0);
                     entityhorseskeleton.setPosition((double) blockposition.getX(), (double) blockposition.getY(), (double) blockposition.getZ());
-                    this.addEntity(entityhorseskeleton);
+                    this.addEntity(entityhorseskeleton, org.bukkit.event.entity.CreatureSpawnEvent.SpawnReason.LIGHTNING); // CraftBukkit
                 }
 
-                this.strikeLightning(new EntityLightning(this, (double) blockposition.getX() + 0.5D, (double) blockposition.getY(), (double) blockposition.getZ() + 0.5D, flag1));
+                this.strikeLightning(new EntityLightning(this, (double) blockposition.getX() + 0.5D, (double) blockposition.getY(), (double) blockposition.getZ() + 0.5D, flag1), org.bukkit.event.weather.LightningStrikeEvent.Cause.WEATHER); // CraftBukkit
             }
         }
 
@@ -338,11 +394,11 @@
             BiomeBase biomebase = this.getBiome(blockposition);
 
             if (biomebase.a((IWorldReader) this, blockposition1)) {
-                this.setTypeUpdate(blockposition1, Blocks.ICE.getBlockData());
+                org.bukkit.craftbukkit.event.CraftEventFactory.handleBlockFormEvent(this, blockposition1, Blocks.ICE.getBlockData(), null); // CraftBukkit
             }
 
             if (flag && biomebase.b(this, blockposition)) {
-                this.setTypeUpdate(blockposition, Blocks.SNOW.getBlockData());
+                org.bukkit.craftbukkit.event.CraftEventFactory.handleBlockFormEvent(this, blockposition, Blocks.SNOW.getBlockData(), null); // CraftBukkit
             }
 
             if (flag && this.getBiome(blockposition1).b() == BiomeBase.Precipitation.RAIN) {
@@ -389,7 +445,7 @@
     protected BlockPosition a(BlockPosition blockposition) {
         BlockPosition blockposition1 = this.getHighestBlockYAt(HeightMap.Type.MOTION_BLOCKING, blockposition);
         AxisAlignedBB axisalignedbb = (new AxisAlignedBB(blockposition1, new BlockPosition(blockposition1.getX(), this.getBuildHeight(), blockposition1.getZ()))).g(3.0D);
-        List<EntityLiving> list = this.a(EntityLiving.class, axisalignedbb, (entityliving) -> {
+        List<EntityLiving> list = this.a(EntityLiving.class, axisalignedbb, (java.util.function.Predicate<EntityLiving>) (entityliving) -> { // CraftBukkit - decompile error
             return entityliving != null && entityliving.isAlive() && this.f(entityliving.getChunkCoordinates());
         });
 
@@ -418,7 +474,7 @@
             while (iterator.hasNext()) {
                 EntityPlayer entityplayer = (EntityPlayer) iterator.next();
 
-                if (entityplayer.isSpectator()) {
+                if (entityplayer.isSpectator() || (entityplayer.fauxSleeping && !entityplayer.isSleeping())) { // CraftBukkit
                     ++i;
                 } else if (entityplayer.isSleeping()) {
                     ++j;
@@ -436,10 +492,22 @@
     }
 
     private void clearWeather() {
-        this.worldData.setWeatherDuration(0);
+        // CraftBukkit start
         this.worldData.setStorm(false);
-        this.worldData.setThunderDuration(0);
+        // If we stop due to everyone sleeping we should reset the weather duration to some other random value.
+        // Not that everyone ever manages to get the whole server to sleep at the same time....
+        if (!this.worldData.hasStorm()) {
+            this.worldData.setWeatherDuration(0);
+        }
+        // CraftBukkit end
         this.worldData.setThundering(false);
+        // CraftBukkit start
+        // If we stop due to everyone sleeping we should reset the weather duration to some other random value.
+        // Not that everyone ever manages to get the whole server to sleep at the same time....
+        if (!this.worldData.isThundering()) {
+            this.worldData.setThunderDuration(0);
+        }
+        // CraftBukkit end
     }
 
     public void resetEmptyTime() {
@@ -477,6 +545,7 @@
                     return IRegistry.ENTITY_TYPE.getKey(entity.getEntityType()).toString();
                 });
                 entity.tick();
+                entity.postTick(); // CraftBukkit
                 this.getMethodProfiler().exit();
             }
 
@@ -562,6 +631,22 @@
             BlockPosition blockposition = worldchunkmanager.a(0, 0, 256, list, random);
             ChunkCoordIntPair chunkcoordintpair = blockposition == null ? new ChunkCoordIntPair(0, 0) : new ChunkCoordIntPair(blockposition);
 
+            // CraftBukkit start
+            if (this.generator != null) {
+                Random rand = new Random(this.getSeed());
+                org.bukkit.Location spawn = this.generator.getFixedSpawnLocation(((WorldServer) this).getWorld(), rand);
+
+                if (spawn != null) {
+                    if (spawn.getWorld() != ((WorldServer) this).getWorld()) {
+                        throw new IllegalStateException("Cannot set spawn point for " + this.worldData.getName() + " to be in another world (" + spawn.getWorld().getName() + ")");
+                    } else {
+                        this.worldData.setSpawn(new BlockPosition(spawn.getBlockX(), spawn.getBlockY(), spawn.getBlockZ()));
+                        return;
+                    }
+                }
+            }
+            // CraftBukkit end
+
             if (blockposition == null) {
                 WorldServer.LOGGER.warn("Unable to find spawn biome");
             }
@@ -637,6 +722,7 @@
         ChunkProviderServer chunkproviderserver = this.getChunkProvider();
 
         if (!flag1) {
+            org.bukkit.Bukkit.getPluginManager().callEvent(new org.bukkit.event.world.WorldSaveEvent(getWorld())); // CraftBukkit
             if (iprogressupdate != null) {
                 iprogressupdate.a(new ChatMessage("menu.savingLevel", new Object[0]));
             }
@@ -648,6 +734,16 @@
 
             chunkproviderserver.save(flag);
         }
+
+        // CraftBukkit start - moved from MinecraftServer.saveChunks
+        // PAIL - rename
+        WorldServer worldserver1 = this;
+        WorldData worlddata = worldserver1.getWorldData();
+
+        worldserver1.getWorldBorder().a(worlddata);
+        worlddata.c(this.server.getBossBattleCustomData().c());
+        worldserver1.getDataManager().saveWorldData(worlddata, this.server.getPlayerList().r());
+        // CraftBukkit end
     }
 
     protected void k_() throws ExceptionWorldConflict {
@@ -719,7 +815,8 @@
             if (entity instanceof EntityInsentient) {
                 EntityInsentient entityinsentient = (EntityInsentient) entity;
 
-                if (entityinsentient.isPersistent() || entityinsentient.I()) {
+                // CraftBukkit - Split out persistent check, don't apply it to special persistent mobs
+                if (entityinsentient.isTypeNotPersistent(0) && entityinsentient.isPersistent()) {
                     continue;
                 }
             }
@@ -736,11 +833,24 @@
 
     @Override
     public boolean addEntity(Entity entity) {
-        return this.addEntity0(entity);
+        // CraftBukkit start
+        return this.addEntity0(entity, CreatureSpawnEvent.SpawnReason.DEFAULT);
+    }
+
+    @Override
+    public boolean addEntity(Entity entity, CreatureSpawnEvent.SpawnReason reason) {
+        return this.addEntity0(entity, reason);
+        // CraftBukkit end
     }
 
     public boolean addEntitySerialized(Entity entity) {
-        return this.addEntity0(entity);
+        // CraftBukkit start
+        return this.addEntitySerialized(entity, CreatureSpawnEvent.SpawnReason.DEFAULT);
+    }
+
+    public boolean addEntitySerialized(Entity entity, CreatureSpawnEvent.SpawnReason reason) {
+        return this.addEntity0(entity, reason);
+        // CraftBukkit end
     }
 
     public void addEntityTeleport(Entity entity) {
@@ -790,13 +900,18 @@
         this.registerEntity(entityplayer);
     }
 
-    private boolean addEntity0(Entity entity) {
+    // CraftBukkit start
+    private boolean addEntity0(Entity entity, CreatureSpawnEvent.SpawnReason spawnReason) {
         if (entity.dead) {
-            WorldServer.LOGGER.warn("Tried to add entity {} but it was marked as removed already", EntityTypes.getName(entity.getEntityType()));
+            // WorldServer.LOGGER.warn("Tried to add entity {} but it was marked as removed already", EntityTypes.getName(entity.getEntityType())); // CraftBukkit
             return false;
         } else if (this.isUUIDTaken(entity)) {
             return false;
         } else {
+            if (!CraftEventFactory.doEntityAddEventCalling(this, entity, spawnReason)) {
+                return false;
+            }
+            // CraftBukkit end
             IChunkAccess ichunkaccess = this.getChunkAt(MathHelper.floor(entity.locX / 16.0D), MathHelper.floor(entity.locZ / 16.0D), ChunkStatus.FULL, entity.attachedToPlayer);
 
             if (!(ichunkaccess instanceof Chunk)) {
@@ -824,7 +939,7 @@
         if (entity1 == null) {
             return false;
         } else {
-            WorldServer.LOGGER.warn("Keeping entity {} that already exists with UUID {}", EntityTypes.getName(entity1.getEntityType()), entity.getUniqueID().toString());
+            // WorldServer.LOGGER.warn("Keeping entity {} that already exists with UUID {}", EntityTypes.getName(entity1.getEntityType()), entity.getUniqueID().toString()); // CraftBukkit
             return true;
         }
     }
@@ -875,10 +990,17 @@
         }
 
         this.getScoreboard().a(entity);
+        // CraftBukkit start - SPIGOT-5278
+        if (entity instanceof EntityDrowned) {
+            this.H.remove(((EntityDrowned) entity).b);
+            this.H.remove(((EntityDrowned) entity).c);
+        } else
+        // CraftBukkit end
         if (entity instanceof EntityInsentient) {
             this.H.remove(((EntityInsentient) entity).getNavigation());
         }
 
+        entity.valid = false; // CraftBukkit
     }
 
     private void registerEntity(Entity entity) {
@@ -899,9 +1021,16 @@
 
             this.entitiesByUUID.put(entity.getUniqueID(), entity);
             this.getChunkProvider().addEntity(entity);
+            // CraftBukkit start - SPIGOT-5278
+            if (entity instanceof EntityDrowned) {
+                this.H.add(((EntityDrowned) entity).b);
+                this.H.add(((EntityDrowned) entity).c);
+            } else
+            // CraftBukkit end
             if (entity instanceof EntityInsentient) {
                 this.H.add(((EntityInsentient) entity).getNavigation());
             }
+            entity.valid = true; // CraftBukkit
         }
 
     }
@@ -932,6 +1061,18 @@
     }
 
     public void strikeLightning(EntityLightning entitylightning) {
+        // CraftBukkit start
+        this.strikeLightning(entitylightning, LightningStrikeEvent.Cause.UNKNOWN);
+    }
+
+    public void strikeLightning(EntityLightning entitylightning, LightningStrikeEvent.Cause cause) {
+        LightningStrikeEvent lightning = new LightningStrikeEvent(this.getWorld(), (org.bukkit.entity.LightningStrike) entitylightning.getBukkitEntity(), cause);
+        this.getServer().getPluginManager().callEvent(lightning);
+
+        if (lightning.isCancelled()) {
+            return;
+        }
+        // CraftBukkit end
         this.globalEntityList.add(entitylightning);
         this.server.getPlayerList().sendPacketNearby((EntityHuman) null, entitylightning.locX, entitylightning.locY, entitylightning.locZ, 512.0D, this.worldProvider.getDimensionManager(), new PacketPlayOutSpawnEntityWeather(entitylightning));
     }
@@ -940,6 +1081,12 @@
     public void a(int i, BlockPosition blockposition, int j) {
         Iterator iterator = this.server.getPlayerList().getPlayers().iterator();
 
+        // CraftBukkit start
+        EntityHuman entityhuman = null;
+        Entity entity = this.getEntity(i);
+        if (entity instanceof EntityHuman) entityhuman = (EntityHuman) entity;
+        // CraftBukkit end
+
         while (iterator.hasNext()) {
             EntityPlayer entityplayer = (EntityPlayer) iterator.next();
 
@@ -948,6 +1095,12 @@
                 double d1 = (double) blockposition.getY() - entityplayer.locY;
                 double d2 = (double) blockposition.getZ() - entityplayer.locZ;
 
+                // CraftBukkit start
+                if (entityhuman != null && entityhuman instanceof EntityPlayer && !entityplayer.getBukkitEntity().canSee(((EntityPlayer) entityhuman).getBukkitEntity())) {
+                    continue;
+                }
+                // CraftBukkit end
+
                 if (d0 * d0 + d1 * d1 + d2 * d2 < 1024.0D) {
                     entityplayer.playerConnection.sendPacket(new PacketPlayOutBlockBreakAnimation(i, blockposition, j));
                 }
@@ -1008,6 +1161,14 @@
 
     @Override
     public Explosion createExplosion(@Nullable Entity entity, DamageSource damagesource, double d0, double d1, double d2, float f, boolean flag, Explosion.Effect explosion_effect) {
+        // CraftBukkit start
+        Explosion explosion = super.createExplosion(entity, damagesource, d0, d1, d2, f, flag, explosion_effect);
+
+        if (explosion.wasCanceled) {
+            return explosion;
+        }
+
+        /* Remove
         Explosion explosion = new Explosion(this, entity, d0, d1, d2, f, flag, explosion_effect);
 
         if (damagesource != null) {
@@ -1016,6 +1177,8 @@
 
         explosion.a();
         explosion.a(false);
+        */
+        // CraftBukkit end - TODO: Check if explosions are still properly implemented
         if (explosion_effect == Explosion.Effect.NONE) {
             explosion.clearBlocks();
         }
@@ -1080,13 +1243,20 @@
     }
 
     public <T extends ParticleParam> int a(T t0, double d0, double d1, double d2, int i, double d3, double d4, double d5, double d6) {
-        PacketPlayOutWorldParticles packetplayoutworldparticles = new PacketPlayOutWorldParticles(t0, false, (float) d0, (float) d1, (float) d2, (float) d3, (float) d4, (float) d5, (float) d6, i);
+        // CraftBukkit - visibility api support
+        return sendParticles(null, t0, d0, d1, d2, i, d3, d4, d5, d6, false);
+    }
+
+    public <T extends ParticleParam> int sendParticles(EntityPlayer sender, T t0, double d0, double d1, double d2, int i, double d3, double d4, double d5, double d6, boolean force) {
+        PacketPlayOutWorldParticles packetplayoutworldparticles = new PacketPlayOutWorldParticles(t0, force, (float) d0, (float) d1, (float) d2, (float) d3, (float) d4, (float) d5, (float) d6, i);
+        // CraftBukkit end
         int j = 0;
 
         for (int k = 0; k < this.players.size(); ++k) {
             EntityPlayer entityplayer = (EntityPlayer) this.players.get(k);
+            if (sender != null && !entityplayer.getBukkitEntity().canSee(sender.getBukkitEntity())) continue; // CraftBukkit
 
-            if (this.a(entityplayer, false, d0, d1, d2, packetplayoutworldparticles)) {
+            if (this.a(entityplayer, force, d0, d1, d2, packetplayoutworldparticles)) { // CraftBukkit
                 ++j;
             }
         }
@@ -1169,7 +1339,13 @@
     @Override
     public WorldMap a(String s) {
         return (WorldMap) this.getMinecraftServer().getWorldServer(DimensionManager.OVERWORLD).getWorldPersistentData().b(() -> {
-            return new WorldMap(s);
+            // CraftBukkit start
+            // We only get here when the data file exists, but is not a valid map
+            WorldMap newMap = new WorldMap(s);
+            MapInitializeEvent event = new MapInitializeEvent(newMap.mapView);
+            Bukkit.getServer().getPluginManager().callEvent(event);
+            return newMap;
+            // CraftBukkit end
         }, s);
     }