SPIGOT-1592: Implement ItemMeta for Spawn Eggs

The Minecraft implementation of spawn eggs is able to construct an entity using all data that is present in the save format, however since the Bukkit API has no such way to construct an entity unattached to a world, and it appears creating such a way is a very challenging task, the decision was instead made to add this API now that 1.11 has entities which may not be represented by data values.
In the future it may be possible to implement a more expanded API cognate with this one.

src/main/java/org/bukkit/craftbukkit/inventory/CraftItemFactory.java

@@ -91,6 +91,8 @@ public final class CraftItemFactory implements ItemFactory {
             return meta instanceof CraftMetaEnchantedBook ? meta : new CraftMetaEnchantedBook(meta);
         case BANNER:
             return meta instanceof CraftMetaBanner ? meta : new CraftMetaBanner(meta);
+        case MONSTER_EGG:
+            return meta instanceof CraftMetaSpawnEgg ? meta : new CraftMetaSpawnEgg(meta);
         case FURNACE:
         case CHEST:
         case TRAPPED_CHEST:

src/main/java/org/bukkit/craftbukkit/inventory/CraftItemStack.java

@@ -348,6 +348,8 @@ public final class CraftItemStack extends ItemStack {
                 return new CraftMetaEnchantedBook(item.getTag());
             case BANNER:
                 return new CraftMetaBanner(item.getTag());
+            case MONSTER_EGG:
+                return new CraftMetaSpawnEgg(item.getTag());
             case FURNACE:
             case CHEST:
             case TRAPPED_CHEST:

src/main/java/org/bukkit/craftbukkit/inventory/CraftMetaItem.java

@@ -115,6 +115,7 @@ class CraftMetaItem implements ItemMeta, Repairable {
                     .put(CraftMetaLeatherArmor.class, "LEATHER_ARMOR")
                     .put(CraftMetaMap.class, "MAP")
                     .put(CraftMetaPotion.class, "POTION")
+                    .put(CraftMetaSpawnEgg.class, "SPAWN_EGG")
                     .put(CraftMetaEnchantedBook.class, "ENCHANTED")
                     .put(CraftMetaFirework.class, "FIREWORK")
                     .put(CraftMetaCharge.class, "FIREWORK_EFFECT")
@@ -839,6 +840,7 @@ class CraftMetaItem implements ItemMeta, Repairable {
                         CraftMetaPotion.DEFAULT_POTION.NBT,
                         CraftMetaSkull.SKULL_OWNER.NBT,
                         CraftMetaSkull.SKULL_PROFILE.NBT,
+                        CraftMetaSpawnEgg.ENTITY_TAG.NBT,
                         CraftMetaBlockState.BLOCK_ENTITY_TAG.NBT,
                         CraftMetaBook.BOOK_TITLE.NBT,
                         CraftMetaBook.BOOK_AUTHOR.NBT,

src/main/java/org/bukkit/craftbukkit/inventory/CraftMetaSpawnEgg.java

@@ -0,0 +1,148 @@
+package org.bukkit.craftbukkit.inventory;
+
+import com.google.common.base.Preconditions;
+import com.google.common.collect.ImmutableMap.Builder;
+import java.util.Map;
+import net.minecraft.server.MinecraftKey;
+import net.minecraft.server.NBTTagCompound;
+import org.bukkit.Material;
+import org.bukkit.configuration.serialization.DelegateDeserialization;
+import org.bukkit.entity.EntityType;
+import org.bukkit.inventory.meta.SpawnEggMeta;
+
+@DelegateDeserialization(CraftMetaItem.SerializableMeta.class)
+public class CraftMetaSpawnEgg extends CraftMetaItem implements SpawnEggMeta {
+
+    static final ItemMetaKey ENTITY_TAG = new ItemMetaKey("EntityTag", "entity-tag");
+    @ItemMetaKey.Specific(ItemMetaKey.Specific.To.NBT)
+    static final ItemMetaKey ENTITY_ID = new ItemMetaKey("id");
+
+    private EntityType spawnedType;
+
+    CraftMetaSpawnEgg(CraftMetaItem meta) {
+        super(meta);
+
+        if (!(meta instanceof CraftMetaSpawnEgg)) {
+            return;
+        }
+
+        CraftMetaSpawnEgg egg = (CraftMetaSpawnEgg) meta;
+        this.spawnedType = egg.spawnedType;
+    }
+
+    CraftMetaSpawnEgg(NBTTagCompound tag) {
+        super(tag);
+
+        if (tag.hasKey(ENTITY_TAG.NBT)) {
+            NBTTagCompound entityTag = tag.getCompound(ENTITY_TAG.NBT);
+
+            if (entityTag.hasKey(ENTITY_ID.NBT)) {
+                this.spawnedType = EntityType.fromName(new MinecraftKey(entityTag.getString(ENTITY_ID.NBT)).a()); // PAIL: rename
+            }
+        }
+    }
+
+    CraftMetaSpawnEgg(Map<String, Object> map) {
+        super(map);
+
+        String entityType = SerializableMeta.getString(map, ENTITY_ID.BUKKIT, true);
+        setSpawnedType(EntityType.fromName(entityType));
+    }
+
+    @Override
+    void applyToItem(NBTTagCompound tag) {
+        super.applyToItem(tag);
+
+        if (hasSpawnedType()) {
+            NBTTagCompound entityTag = new NBTTagCompound();
+            entityTag.setString(ENTITY_ID.NBT, new MinecraftKey(spawnedType.getName()).toString());
+
+            tag.set(ENTITY_TAG.NBT, entityTag);
+        }
+    }
+
+    @Override
+    boolean applicableTo(Material type) {
+        switch (type) {
+            case MONSTER_EGG:
+                return true;
+            default:
+                return false;
+        }
+    }
+
+    @Override
+    boolean isEmpty() {
+        return super.isEmpty() && isSpawnEggEmpty();
+    }
+
+    boolean isSpawnEggEmpty() {
+        return !hasSpawnedType();
+    }
+
+    boolean hasSpawnedType() {
+        return spawnedType != null;
+    }
+
+    @Override
+    public EntityType getSpawnedType() {
+        return spawnedType;
+    }
+
+    @Override
+    public void setSpawnedType(EntityType type) {
+        Preconditions.checkArgument(type == null || type.getName() != null, "Spawn egg type must have name (%s)", type);
+
+        this.spawnedType = type;
+    }
+
+    @Override
+    boolean equalsCommon(CraftMetaItem meta) {
+        if (!super.equalsCommon(meta)) {
+            return false;
+        }
+        if (meta instanceof CraftMetaSpawnEgg) {
+            CraftMetaSpawnEgg that = (CraftMetaSpawnEgg) meta;
+
+            return hasSpawnedType() ? that.hasSpawnedType() && this.spawnedType.equals(that.spawnedType) : !that.hasSpawnedType();
+        }
+        return true;
+    }
+
+    @Override
+    boolean notUncommon(CraftMetaItem meta) {
+        return super.notUncommon(meta) && (meta instanceof CraftMetaSpawnEgg || isSpawnEggEmpty());
+    }
+
+    @Override
+    int applyHash() {
+        final int original;
+        int hash = original = super.applyHash();
+
+        if (hasSpawnedType()) {
+            hash = 73 * hash + spawnedType.hashCode();
+        }
+
+        return original != hash ? CraftMetaSpawnEgg.class.hashCode() ^ hash : hash;
+    }
+
+    @Override
+    Builder<String, Object> serialize(Builder<String, Object> builder) {
+        super.serialize(builder);
+
+        if (hasSpawnedType()) {
+            builder.put(ENTITY_ID.BUKKIT, spawnedType.getName());
+        }
+
+        return builder;
+    }
+
+    @Override
+    public CraftMetaSpawnEgg clone() {
+        CraftMetaSpawnEgg clone = (CraftMetaSpawnEgg) super.clone();
+
+        clone.spawnedType = spawnedType;
+
+        return clone;
+    }
+}

src/test/java/org/bukkit/craftbukkit/inventory/ItemMetaTest.java

@@ -24,6 +24,7 @@ import org.bukkit.craftbukkit.inventory.ItemStackTest.StackWrapper;
 import org.bukkit.craftbukkit.inventory.ItemStackTest.BukkitWrapper;
 import org.bukkit.craftbukkit.inventory.ItemStackTest.CraftWrapper;
 import org.bukkit.enchantments.Enchantment;
+import org.bukkit.entity.EntityType;
 import org.bukkit.inventory.ItemStack;
 import org.bukkit.inventory.meta.BannerMeta;
 import org.bukkit.inventory.meta.BlockStateMeta;
@@ -35,6 +36,7 @@ import org.bukkit.inventory.meta.ItemMeta;
 import org.bukkit.inventory.meta.LeatherArmorMeta;
 import org.bukkit.inventory.meta.MapMeta;
 import org.bukkit.inventory.meta.PotionMeta;
+import org.bukkit.inventory.meta.SpawnEggMeta;
 import org.bukkit.potion.PotionEffectType;
 import org.bukkit.potion.PotionData;
 import org.bukkit.potion.PotionType;
@@ -255,6 +257,14 @@ public class ItemMetaTest extends AbstractTestingBase {
                     cleanStack.setItemMeta(meta);
                     return cleanStack;
                 }
+            }, 
+            new StackProvider(Material.MONSTER_EGG) {
+                @Override ItemStack operate(ItemStack cleanStack) {
+                    final SpawnEggMeta meta = (SpawnEggMeta) cleanStack.getItemMeta();
+                    meta.setSpawnedType(EntityType.ZOMBIE);
+                    cleanStack.setItemMeta(meta);
+                    return cleanStack;
+                }
             }
         );