SPIGOT-5732, SPIGOT-6387: Overhaul Hanging entities

- SPIGOT-5732: Fix issue with spawning leash hitches and painting, by using the right block faces

- SPIGOT-6387: Allow hanging entities to be spawned mid air

- Use randomize parameter to determine if a random painting should be chosen or not

- Return BlockFace self by leash hitches entity

- Throw a standardised exception when trying to set a BlockFace to a hanging entity which the entity does not support, instead of using BlockFace south or throwing a null pointer

By: DerFrZocker <derrieple@gmail.com>

paper-server/src/main/java/org/bukkit/craftbukkit/entity/CraftHanging.java

@@ -29,7 +29,6 @@ public class CraftHanging extends CraftEntity implements Hanging {
         EnumDirection dir = hanging.getDirection();
         switch (face) {
             case SOUTH:
-            default:
                 getHandle().setDirection(EnumDirection.SOUTH);
                 break;
             case WEST:
@@ -41,6 +40,8 @@ public class CraftHanging extends CraftEntity implements Hanging {
             case EAST:
                 getHandle().setDirection(EnumDirection.EAST);
                 break;
+            default:
+                throw new IllegalArgumentException(String.format("%s is not a valid facing direction", face));
         }
         if (!force && !getHandle().generation && !hanging.survives()) {
             // Revert since it doesn't fit

paper-server/src/main/java/org/bukkit/craftbukkit/entity/CraftItemFrame.java

@@ -26,6 +26,8 @@ public class CraftItemFrame extends CraftHanging implements ItemFrame {
         EnumDirection oldDir = hanging.getDirection();
         EnumDirection newDir = CraftBlock.blockFaceToNotch(face);
 
+        Preconditions.checkArgument(newDir != null, "%s is not a valid facing direction", face);
+
         getHandle().setDirection(newDir);
         if (!force && !getHandle().generation && !hanging.survives()) {
             hanging.setDirection(oldDir);

paper-server/src/main/java/org/bukkit/craftbukkit/entity/CraftLeash.java

@@ -1,6 +1,8 @@
 package org.bukkit.craftbukkit.entity;
 
+import com.google.common.base.Preconditions;
 import net.minecraft.world.entity.decoration.EntityLeash;
+import org.bukkit.block.BlockFace;
 import org.bukkit.craftbukkit.CraftServer;
 import org.bukkit.entity.EntityType;
 import org.bukkit.entity.LeashHitch;
@@ -10,6 +12,19 @@ public class CraftLeash extends CraftHanging implements LeashHitch {
         super(server, entity);
     }
 
+    @Override
+    public boolean setFacingDirection(BlockFace face, boolean force) {
+        Preconditions.checkArgument(face == BlockFace.SELF, "%s is not a valid facing direction", face);
+
+        return force || getHandle().generation || getHandle().survives();
+    }
+
+    @Override
+    public BlockFace getFacing() {
+        // Leash hitch has no facing direction, so we return self
+        return BlockFace.SELF;
+    }
+
     @Override
     public EntityLeash getHandle() {
         return (EntityLeash) entity;