Add EntityLeash and ItemLeash for diff visibility

src/main/java/net/minecraft/server/ItemLeash.java

@@ -0,0 +1,53 @@
+package net.minecraft.server;
+
+import java.util.Iterator;
+import java.util.List;
+
+public class ItemLeash extends Item {
+
+    public ItemLeash(int i) {
+        super(i);
+        this.a(CreativeModeTab.i);
+    }
+
+    public boolean interactWith(ItemStack itemstack, EntityHuman entityhuman, World world, int i, int j, int k, int l, float f, float f1, float f2) {
+        int i1 = world.getTypeId(i, j, k);
+
+        if (Block.byId[i1] != null && Block.byId[i1].d() == 11) {
+            if (world.isStatic) {
+                return true;
+            } else {
+                a(entityhuman, world, i, j, k);
+                return true;
+            }
+        } else {
+            return false;
+        }
+    }
+
+    public static boolean a(EntityHuman entityhuman, World world, int i, int j, int k) {
+        EntityLeash entityleash = EntityLeash.b(world, i, j, k);
+        boolean flag = false;
+        double d0 = 7.0D;
+        List list = world.a(EntityInsentient.class, AxisAlignedBB.a().a((double) i - d0, (double) j - d0, (double) k - d0, (double) i + d0, (double) j + d0, (double) k + d0));
+
+        if (list != null) {
+            Iterator iterator = list.iterator();
+
+            while (iterator.hasNext()) {
+                EntityInsentient entityinsentient = (EntityInsentient) iterator.next();
+
+                if (entityinsentient.bH() && entityinsentient.bI() == entityhuman) {
+                    if (entityleash == null) {
+                        entityleash = EntityLeash.a(world, i, j, k);
+                    }
+
+                    entityinsentient.b(entityleash, true);
+                    flag = true;
+                }
+            }
+        }
+
+        return flag;
+    }
+}