--- a/net/minecraft/server/World.java
+++ b/net/minecraft/server/World.java
@@ -21,6 +21,23 @@
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 
+// CraftBukkit start
+import com.google.common.collect.Maps;
+import java.util.Map;
+import org.bukkit.Bukkit;
+import org.bukkit.block.BlockState;
+import org.bukkit.craftbukkit.CraftServer;
+import org.bukkit.craftbukkit.CraftWorld;
+import org.bukkit.craftbukkit.block.CraftBlockState;
+import org.bukkit.craftbukkit.block.data.CraftBlockData;
+import org.bukkit.craftbukkit.event.CraftEventFactory;
+import org.bukkit.craftbukkit.util.CraftMagicNumbers;
+import org.bukkit.event.block.BlockCanBuildEvent;
+import org.bukkit.event.block.BlockPhysicsEvent;
+import org.bukkit.event.entity.CreatureSpawnEvent.SpawnReason;
+import org.bukkit.generator.ChunkGenerator;
+// CraftBukkit end
+
 public abstract class World implements IEntityAccess, GeneratorAccess, IIBlockAccess, AutoCloseable {
 
     protected static final Logger e = LogManager.getLogger();
@@ -62,7 +79,52 @@
     private final WorldBorder K;
     int[] E;
 
-    protected World(IDataManager idatamanager, @Nullable PersistentCollection persistentcollection, WorldData worlddata, WorldProvider worldprovider, MethodProfiler methodprofiler, boolean flag) {
+    // CraftBukkit start Added the following
+    private final CraftWorld world;
+    public boolean pvpMode;
+    public boolean keepSpawnInMemory = true;
+    public ChunkGenerator generator;
+
+    public boolean captureBlockStates = false;
+    public boolean captureTreeGeneration = false;
+    public ArrayList<CraftBlockState> capturedBlockStates = new ArrayList<CraftBlockState>() {
+        @Override
+        public boolean add(CraftBlockState blockState) {
+            Iterator<CraftBlockState> blockStateIterator = this.iterator();
+            while (blockStateIterator.hasNext()) {
+                BlockState blockState1 = blockStateIterator.next();
+                if (blockState1.getLocation().equals(blockState.getLocation())) {
+                    return false;
+                }
+            }
+
+            return super.add(blockState);
+        }
+    };
+    public List<EntityItem> captureDrops;
+    public long ticksPerAnimalSpawns;
+    public long ticksPerMonsterSpawns;
+    public boolean populating;
+    private int tickPosition;
+
+    public CraftWorld getWorld() {
+        return this.world;
+    }
+
+    public CraftServer getServer() {
+        return (CraftServer) Bukkit.getServer();
+    }
+
+    public Chunk getChunkIfLoaded(int x, int z) {
+        return ((ChunkProviderServer) this.chunkProvider).getChunkAt(x, z, false, false);
+    }
+
+    protected World(IDataManager idatamanager, @Nullable PersistentCollection persistentcollection, WorldData worlddata, WorldProvider worldprovider, MethodProfiler methodprofiler, boolean flag, ChunkGenerator gen, org.bukkit.World.Environment env) {
+        this.generator = gen;
+        this.world = new CraftWorld((WorldServer) this, gen, env);
+        this.ticksPerAnimalSpawns = this.getServer().getTicksPerAnimalSpawns(); // CraftBukkit
+        this.ticksPerMonsterSpawns = this.getServer().getTicksPerMonsterSpawns(); // CraftBukkit
+        // CraftBukkit end
         this.v = Lists.newArrayList(new IWorldAccess[] { this.u});
         this.allowMonsters = true;
         this.allowAnimals = true;
@@ -74,6 +136,36 @@
         this.worldProvider = worldprovider;
         this.isClientSide = flag;
         this.K = worldprovider.getWorldBorder();
+        // CraftBukkit start
+        getWorldBorder().world = (WorldServer) this;
+        // From PlayerList.setPlayerFileData
+        getWorldBorder().a(new IWorldBorderListener() {
+            public void a(WorldBorder worldborder, double d0) {
+                getServer().getHandle().sendAll(new PacketPlayOutWorldBorder(worldborder, PacketPlayOutWorldBorder.EnumWorldBorderAction.SET_SIZE), worldborder.world);
+            }
+
+            public void a(WorldBorder worldborder, double d0, double d1, long i) {
+                getServer().getHandle().sendAll(new PacketPlayOutWorldBorder(worldborder, PacketPlayOutWorldBorder.EnumWorldBorderAction.LERP_SIZE), worldborder.world);
+            }
+
+            public void a(WorldBorder worldborder, double d0, double d1) {
+                getServer().getHandle().sendAll(new PacketPlayOutWorldBorder(worldborder, PacketPlayOutWorldBorder.EnumWorldBorderAction.SET_CENTER), worldborder.world);
+            }
+
+            public void a(WorldBorder worldborder, int i) {
+                getServer().getHandle().sendAll(new PacketPlayOutWorldBorder(worldborder, PacketPlayOutWorldBorder.EnumWorldBorderAction.SET_WARNING_TIME), worldborder.world);
+            }
+
+            public void b(WorldBorder worldborder, int i) {
+                getServer().getHandle().sendAll(new PacketPlayOutWorldBorder(worldborder, PacketPlayOutWorldBorder.EnumWorldBorderAction.SET_WARNING_BLOCKS), worldborder.world);
+            }
+
+            public void b(WorldBorder worldborder, double d0) {}
+
+            public void c(WorldBorder worldborder, double d0) {}
+        });
+        this.getServer().addWorld(this.world);
+        // CraftBukkit end
     }
 
     public BiomeBase getBiome(BlockPosition blockposition) {
@@ -148,6 +240,26 @@
     }
 
     public boolean setTypeAndData(BlockPosition blockposition, IBlockData iblockdata, int i) {
+        // CraftBukkit start - tree generation
+        if (this.captureTreeGeneration) {
+            CraftBlockState blockstate = null;
+            Iterator<CraftBlockState> it = capturedBlockStates.iterator();
+            while (it.hasNext()) {
+                CraftBlockState previous = it.next();
+                if (previous.getPosition().equals(blockposition)) {
+                    blockstate = previous;
+                    it.remove();
+                    break;
+                }
+            }
+            if (blockstate == null) {
+                blockstate = org.bukkit.craftbukkit.block.CraftBlockState.getBlockState(this, blockposition, i);
+            }
+            blockstate.setData(iblockdata);
+            this.capturedBlockStates.add(blockstate);
+            return true;
+        }
+        // CraftBukkit end
         if (k(blockposition)) {
             return false;
         } else if (!this.isClientSide && this.worldData.getType() == WorldType.DEBUG_ALL_BLOCK_STATES) {
@@ -155,9 +267,23 @@
         } else {
             Chunk chunk = this.getChunkAtWorldCoords(blockposition);
             Block block = iblockdata.getBlock();
-            IBlockData iblockdata1 = chunk.setType(blockposition, iblockdata, (i & 64) != 0);
+
+            // CraftBukkit start - capture blockstates
+            CraftBlockState blockstate = null;
+            if (this.captureBlockStates) {
+                blockstate = org.bukkit.craftbukkit.block.CraftBlockState.getBlockState(this, blockposition, i);
+                this.capturedBlockStates.add(blockstate);
+            }
+            // CraftBukkit end
+
+            IBlockData iblockdata1 = chunk.setType(blockposition, iblockdata, (i & 64) != 0, (i & 1024) == 0); // CraftBukkit custom NO_PLACE flag
 
             if (iblockdata1 == null) {
+                // CraftBukkit start - remove blockstate if failed
+                if (this.captureBlockStates) {
+                    this.capturedBlockStates.remove(blockstate);
+                }
+                // CraftBukkit end
                 return false;
             } else {
                 IBlockData iblockdata2 = this.getType(blockposition);
@@ -168,6 +294,7 @@
                     this.methodProfiler.exit();
                 }
 
+                /*
                 if (iblockdata2 == iblockdata) {
                     if (iblockdata1 != iblockdata2) {
                         this.a(blockposition, blockposition);
@@ -192,12 +319,63 @@
                         iblockdata.b(this, blockposition, j);
                     }
                 }
+                */
+
+                // CraftBukkit start
+                if (!this.captureBlockStates) { // Don't notify clients or update physics while capturing blockstates
+                    // Modularize client and physic updates
+                    notifyAndUpdatePhysics(blockposition, chunk, iblockdata1, iblockdata, iblockdata2, i);
+                }
+                // CraftBukkit end
 
                 return true;
             }
         }
     }
 
+    // CraftBukkit start - Split off from above in order to directly send client and physic updates
+    public void notifyAndUpdatePhysics(BlockPosition blockposition, Chunk chunk, IBlockData oldBlock, IBlockData newBlock, IBlockData actualBlock, int i) {
+        IBlockData iblockdata = newBlock;
+        IBlockData iblockdata1 = oldBlock;
+        IBlockData iblockdata2 = actualBlock;
+        if (iblockdata2 == iblockdata) {
+            if (iblockdata1 != iblockdata2) {
+                this.a(blockposition, blockposition);
+            }
+
+            if ((i & 2) != 0 && (!this.isClientSide || (i & 4) == 0) && (chunk == null || chunk.isReady())) {  // allow chunk to be null here as chunk.isReady() is false when we send our notification during block placement
+                this.notify(blockposition, iblockdata1, iblockdata, i);
+            }
+
+            if (!this.isClientSide && (i & 1) != 0) {
+                this.update(blockposition, iblockdata1.getBlock());
+                if (iblockdata.isComplexRedstone()) {
+                    this.updateAdjacentComparators(blockposition, newBlock.getBlock());
+                }
+            }
+
+            if ((i & 16) == 0) {
+                int j = i & -2;
+
+                // CraftBukkit start
+                iblockdata1.b(this, blockposition, j); // Don't call an event for the old block to limit event spam
+                CraftWorld world = ((WorldServer) this).getWorld();
+                if (world != null) {
+                    BlockPhysicsEvent event = new BlockPhysicsEvent(world.getBlockAt(blockposition.getX(), blockposition.getY(), blockposition.getZ()), CraftBlockData.fromData(iblockdata));
+                    this.getServer().getPluginManager().callEvent(event);
+
+                    if (event.isCancelled()) {
+                        return;
+                    }
+                }
+                // CraftBukkit end
+                iblockdata.a((GeneratorAccess) this, blockposition, j);
+                iblockdata.b(this, blockposition, j);
+            }
+        }
+    }
+    // CraftBukkit end
+
     public boolean setAir(BlockPosition blockposition) {
         Fluid fluid = this.getFluid(blockposition);
 
@@ -234,6 +412,11 @@
 
     public void update(BlockPosition blockposition, Block block) {
         if (this.worldData.getType() != WorldType.DEBUG_ALL_BLOCK_STATES) {
+            // CraftBukkit start
+            if (populating) {
+                return;
+            }
+            // CraftBukkit end
             this.applyPhysics(blockposition, block);
         }
 
@@ -309,6 +492,17 @@
             IBlockData iblockdata = this.getType(blockposition);
 
             try {
+                // CraftBukkit start
+                CraftWorld world = ((WorldServer) this).getWorld();
+                if (world != null) {
+                    BlockPhysicsEvent event = new BlockPhysicsEvent(world.getBlockAt(blockposition.getX(), blockposition.getY(), blockposition.getZ()), CraftBlockData.fromData(iblockdata));
+                    this.getServer().getPluginManager().callEvent(event);
+
+                    if (event.isCancelled()) {
+                        return;
+                    }
+                }
+                // CraftBukkit end
                 iblockdata.doPhysics(this, blockposition, block, blockposition1);
             } catch (Throwable throwable) {
                 CrashReport crashreport = CrashReport.a(throwable, "Exception while updating neighbours");
@@ -317,7 +511,7 @@
                 crashreportsystemdetails.a("Source block type", () -> {
                     try {
                         return String.format("ID #%s (%s // %s)", new Object[] { IRegistry.BLOCK.getKey(block), block.m(), block.getClass().getCanonicalName()});
-                    } catch (Throwable throwable) {
+                    } catch (Throwable throwablex) { // CraftBukkit - decompile error
                         return "ID #" + IRegistry.BLOCK.getKey(block);
                     }
                 });
@@ -403,6 +597,17 @@
     }
 
     public IBlockData getType(BlockPosition blockposition) {
+        // CraftBukkit start - tree generation
+        if (captureTreeGeneration) {
+            Iterator<CraftBlockState> it = capturedBlockStates.iterator();
+            while (it.hasNext()) {
+                CraftBlockState previous = it.next();
+                if (previous.getPosition().equals(blockposition)) {
+                    return previous.getHandle();
+                }
+            }
+        }
+        // CraftBukkit end
         if (k(blockposition)) {
             return Blocks.VOID_AIR.getBlockData();
         } else {
@@ -649,6 +854,16 @@
     }
 
     public boolean addEntity(Entity entity) {
+        // CraftBukkit start - Used for entities other than creatures
+        return addEntity(entity, SpawnReason.DEFAULT);
+    }
+
+    public boolean addEntity(Entity entity, SpawnReason spawnReason) { // Changed signature, added SpawnReason
+        if (!CraftEventFactory.doEntityAddEventCalling(this, entity, spawnReason)) {
+            return false;
+        }
+        // CraftBukkit end
+
         int i = MathHelper.floor(entity.locX / 16.0D);
         int j = MathHelper.floor(entity.locZ / 16.0D);
         boolean flag = entity.attachedToPlayer;
@@ -679,6 +894,7 @@
             ((IWorldAccess) this.v.get(i)).a(entity);
         }
 
+        entity.valid = true; // CraftBukkit
     }
 
     protected void c(Entity entity) {
@@ -686,6 +902,7 @@
             ((IWorldAccess) this.v.get(i)).b(entity);
         }
 
+        entity.valid = false; // CraftBukkit
     }
 
     public void kill(Entity entity) {
@@ -721,7 +938,15 @@
             this.getChunkAt(i, j).b(entity);
         }
 
-        this.entityList.remove(entity);
+        // CraftBukkit start - Decrement loop variable field if we've already ticked this entity
+        int index = this.entityList.indexOf(entity);
+        if (index != -1) {
+            if (index <= this.tickPosition) {
+                this.tickPosition--;
+            }
+            this.entityList.remove(index);
+        }
+        // CraftBukkit end
         this.c(entity);
     }
 
@@ -756,6 +981,11 @@
 
         for (i = 0; i < this.k.size(); ++i) {
             entity = (Entity) this.k.get(i);
+            // CraftBukkit start - Fixed an NPE
+            if (entity == null) {
+                continue;
+            }
+            // CraftBukkit end
 
             try {
                 ++entity.ticksLived;
@@ -804,8 +1034,10 @@
         CrashReport crashreport1;
         CrashReportSystemDetails crashreportsystemdetails1;
 
-        for (i = 0; i < this.entityList.size(); ++i) {
-            entity = (Entity) this.entityList.get(i);
+        // CraftBukkit start - Use field for loop variable
+        for (this.tickPosition = 0; this.tickPosition < this.entityList.size(); ++this.tickPosition) {
+            entity = (Entity) this.entityList.get(this.tickPosition);
+            // CraftBukkit end
             Entity entity1 = entity.getVehicle();
 
             if (entity1 != null) {
@@ -838,7 +1070,7 @@
                     this.getChunkAt(j, l).b(entity);
                 }
 
-                this.entityList.remove(i--);
+                this.entityList.remove(this.tickPosition--); // CraftBukkit - Use field for loop variable
                 this.c(entity);
             }
 
@@ -893,9 +1125,11 @@
                 TileEntity tileentity1 = (TileEntity) this.c.get(i1);
 
                 if (!tileentity1.x()) {
+                    /* CraftBukkit start - Order matters, moved down
                     if (!this.tileEntityList.contains(tileentity1)) {
                         this.a(tileentity1);
                     }
+                    // CraftBukkit end */
 
                     if (this.isLoaded(tileentity1.getPosition())) {
                         Chunk chunk = this.getChunkAtWorldCoords(tileentity1.getPosition());
@@ -903,6 +1137,12 @@
 
                         chunk.a(tileentity1.getPosition(), tileentity1);
                         this.notify(tileentity1.getPosition(), iblockdata, iblockdata, 3);
+                        // CraftBukkit start
+                        // From above, don't screw this up - SPIGOT-1746
+                        if (!this.tileEntityList.contains(tileentity1)) {
+                            this.a(tileentity1);
+                        }
+                        // CraftBukkit end
                     }
                 }
             }
@@ -956,15 +1196,13 @@
         int i;
         int j;
 
-        if (!(entity instanceof EntityHuman)) {
-            i = MathHelper.floor(entity.locX);
-            j = MathHelper.floor(entity.locZ);
-            boolean flag1 = true;
-
-            if (flag && !this.isAreaLoaded(i - 32, 0, j - 32, i + 32, 0, j + 32, true)) {
-                return;
-            }
+        // CraftBukkit start - check if chunks are loaded as done in previous versions
+        // TODO: Go back to Vanilla behaviour when comfortable
+        Chunk startingChunk = this.getChunkIfLoaded(MathHelper.floor(entity.locX) >> 4, MathHelper.floor(entity.locZ) >> 4);
+        if (flag && !(startingChunk != null && startingChunk.areNeighborsLoaded(2))) {
+            return;
         }
+        // CraftBukkit end
 
         entity.N = entity.locX;
         entity.O = entity.locY;
@@ -980,6 +1218,7 @@
                     return IRegistry.ENTITY_TYPE.getKey(entity.P()).toString();
                 });
                 entity.tick();
+                entity.postTick(); // CraftBukkit
                 this.methodProfiler.exit();
             }
         }
@@ -1310,11 +1549,18 @@
         }
     }
 
+    public Map<BlockPosition, TileEntity> capturedTileEntities = Maps.newHashMap();
     @Nullable
     public TileEntity getTileEntity(BlockPosition blockposition) {
         if (k(blockposition)) {
             return null;
         } else {
+            // CraftBukkit start
+            if (capturedTileEntities.containsKey(blockposition)) {
+                return capturedTileEntities.get(blockposition);
+            }
+            // CraftBukkit end
+
             TileEntity tileentity = null;
 
             if (this.J) {
@@ -1349,6 +1595,14 @@
     public void setTileEntity(BlockPosition blockposition, @Nullable TileEntity tileentity) {
         if (!k(blockposition)) {
             if (tileentity != null && !tileentity.x()) {
+                // CraftBukkit start
+                if (captureBlockStates) {
+                    tileentity.setWorld(this);
+                    tileentity.setPosition(blockposition);
+                    capturedTileEntities.put(blockposition, tileentity);
+                    return;
+                }
+                // CraftBukkit end
                 if (this.J) {
                     tileentity.setPosition(blockposition);
                     Iterator iterator = this.c.iterator();
@@ -1509,6 +1763,14 @@
                 }
 
                 this.p = MathHelper.a(this.p, 0.0F, 1.0F);
+
+                // CraftBukkit start
+                for (int idx = 0; idx < this.players.size(); ++idx) {
+                    if (((EntityPlayer) this.players.get(idx)).world == this) {
+                        ((EntityPlayer) this.players.get(idx)).tickWeather();
+                    }
+                }
+                // CraftBukkit end
             }
         }
     }
@@ -1594,7 +1856,10 @@
     }
 
     public boolean c(EnumSkyBlock enumskyblock, BlockPosition blockposition) {
-        if (!this.areChunksLoaded(blockposition, 17, false)) {
+        // CraftBukkit start - Use neighbor cache instead of looking up
+        Chunk chunk = this.getChunkIfLoaded(blockposition.getX() >> 4, blockposition.getZ() >> 4);
+        if (chunk == null || !chunk.areNeighborsLoaded(1) /*!this.areChunksLoaded(blockposition, 17, false)*/) {
+            // CraftBukkit end
             return false;
         } else {
             int i = 0;
@@ -1737,7 +2002,7 @@
     }
 
     public Stream<VoxelShape> a(@Nullable Entity entity, VoxelShape voxelshape, VoxelShape voxelshape1, Set<Entity> set) {
-        Stream stream = super.a(entity, voxelshape, voxelshape1, set);
+        Stream stream = IIBlockAccess.super.a(entity, voxelshape, voxelshape1, set); // CraftBukkit - decompile error
 
         return entity == null ? stream : Stream.concat(stream, this.a(entity, voxelshape, set));
     }
@@ -1767,7 +2032,7 @@
         while (iterator.hasNext()) {
             Entity entity = (Entity) iterator.next();
 
-            if (oclass.isAssignableFrom(entity.getClass()) && predicate.test(entity)) {
+            if (oclass.isAssignableFrom(entity.getClass()) && predicate.test((T) entity)) {
                 arraylist.add(entity);
             }
         }
@@ -1782,7 +2047,7 @@
         while (iterator.hasNext()) {
             Entity entity = (Entity) iterator.next();
 
-            if (oclass.isAssignableFrom(entity.getClass()) && predicate.test(entity)) {
+            if (oclass.isAssignableFrom(entity.getClass()) && predicate.test((T) entity)) { // CraftBukkit - fix decompile error
                 arraylist.add(entity);
             }
         }
@@ -1831,7 +2096,7 @@
             }
         }
 
-        return entity;
+        return (T) entity; // CraftBukkit fix decompile error
     }
 
     @Nullable
@@ -1852,8 +2117,16 @@
 
         while (iterator.hasNext()) {
             Entity entity = (Entity) iterator.next();
+            // CraftBukkit start - Split out persistent check, don't apply it to special persistent mobs
+            if (entity instanceof EntityInsentient) {
+                EntityInsentient entityinsentient = (EntityInsentient) entity;
+                if (entityinsentient.isTypeNotPersistent() && entityinsentient.isPersistent()) {
+                    continue;
+                }
+            }
 
-            if (!(entity instanceof EntityInsentient) || !((EntityInsentient) entity).isPersistent()) {
+            if (true || !(entity instanceof EntityInsentient) || !((EntityInsentient) entity).isPersistent()) {
+                // CraftBukkit end
                 if (oclass.isAssignableFrom(entity.getClass())) {
                     ++j;
                 }
@@ -1972,6 +2245,11 @@
 
         for (int i = 0; i < this.players.size(); ++i) {
             EntityHuman entityhuman1 = (EntityHuman) this.players.get(i);
+            // CraftBukkit start - Fixed an NPE
+            if (entityhuman1 == null || entityhuman1.dead) {
+                continue;
+            }
+            // CraftBukkit end
 
             if (predicate.test(entityhuman1)) {
                 double d5 = entityhuman1.d(d0, d1, d2);
@@ -2185,6 +2463,16 @@
 
     public void everyoneSleeping() {}
 
+    // CraftBukkit start
+    // Calls the method that checks to see if players are sleeping
+    // Called by CraftPlayer.setPermanentSleeping()
+    public void checkSleepStatus() {
+        if (!this.isClientSide) {
+            this.everyoneSleeping();
+        }
+    }
+    // CraftBukkit end
+
     public float g(float f) {
         return (this.q + (this.r - this.q) * f) * this.i(f);
     }
@@ -2346,7 +2634,7 @@
         int l = j * 16 + 8 - blockposition.getZ();
         boolean flag = true;
 
-        return k >= -128 && k <= 128 && l >= -128 && l <= 128;
+        return k >= -128 && k <= 128 && l >= -128 && l <= 128 && this.keepSpawnInMemory; // CraftBukkit - Added 'this.keepSpawnInMemory'
     }
 
     public LongSet ag() {