Support for MerchantRecipeList (#894)

* Added support for MerchantRecipeList found in OPEN_WINDOW_MERCHANT of MC versions 1.13+

src/main/java/com/comphenix/protocol/events/PacketContainer.java

@@ -61,6 +61,7 @@ import org.bukkit.WorldType;
 import org.bukkit.entity.Entity;
 import org.bukkit.entity.EntityType;
 import org.bukkit.inventory.ItemStack;
+import org.bukkit.inventory.MerchantRecipe;
 import org.bukkit.potion.PotionEffectType;
 import org.bukkit.util.Vector;
 
@@ -937,6 +938,17 @@ public class PacketContainer implements Serializable {
 				BukkitConverters.getDimensionIDConverter()
 		);
     }
+	
+	/**
+	 * Retrieve a read/write structure for the MerchantRecipeList class.
+	 * @return A modifier for MerchantRecipeList fields.
+	 */
+	public StructureModifier<List<MerchantRecipe>> getMerchantRecipeLists() {
+		return structureModifier.withType(
+				MinecraftReflection.getMinecraftClass("MerchantRecipeList"),
+				BukkitConverters.getMerchantRecipeListConverter()
+		);
+    }
 
 	/**
 	 * Retrieve a read/write structure for ItemSlot/ItemStack pair lists in 1.16+

src/main/java/com/comphenix/protocol/wrappers/BukkitConverters.java

@@ -25,6 +25,7 @@ import java.util.*;
 import java.util.Map.Entry;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.function.Supplier;
+import java.util.stream.Collectors;
 
 import com.comphenix.protocol.PacketType;
 import com.comphenix.protocol.ProtocolLibrary;
@@ -38,6 +39,7 @@ import com.comphenix.protocol.reflect.FieldAccessException;
 import com.comphenix.protocol.reflect.FuzzyReflection;
 import com.comphenix.protocol.reflect.StructureModifier;
 import com.comphenix.protocol.reflect.accessors.Accessors;
+import com.comphenix.protocol.reflect.accessors.ConstructorAccessor;
 import com.comphenix.protocol.reflect.accessors.FieldAccessor;
 import com.comphenix.protocol.reflect.accessors.MethodAccessor;
 import com.comphenix.protocol.reflect.fuzzy.FuzzyMethodContract;
@@ -60,6 +62,7 @@ import org.bukkit.advancement.Advancement;
 import org.bukkit.entity.Entity;
 import org.bukkit.entity.EntityType;
 import org.bukkit.inventory.ItemStack;
+import org.bukkit.inventory.MerchantRecipe;
 import org.bukkit.potion.PotionEffect;
 import org.bukkit.potion.PotionEffectType;
 import org.bukkit.util.Vector;
@@ -1237,4 +1240,54 @@ public class BukkitConverters {
 			}
 		});
 	}
+	
+	private static ConstructorAccessor merchantRecipeListConstructor = null;
+	private static MethodAccessor bukkitMerchantRecipeToCraft = null;
+	private static MethodAccessor craftMerchantRecipeToNMS = null;
+	private static MethodAccessor nmsMerchantRecipeToBukkit = null;
+	
+	/**
+	 * Creates a converter from a MerchantRecipeList (which is just an ArrayList of MerchantRecipe wrapper)
+	 * to a {@link List} of {@link MerchantRecipe}. Primarily for the packet OPEN_WINDOW_MERCHANT which is present
+	 * in 1.13+.
+	 *
+	 * @return The MerchantRecipeList converter.
+	 */
+	public static EquivalentConverter<List<MerchantRecipe>> getMerchantRecipeListConverter() {
+		return ignoreNull(new EquivalentConverter<List<MerchantRecipe>>() {
+			
+			@Override
+			public Object getGeneric(List<MerchantRecipe> specific) {
+				if (merchantRecipeListConstructor == null) {
+					Class<?> merchantRecipeListClass = MinecraftReflection.getMinecraftClass("MerchantRecipeList");
+					merchantRecipeListConstructor = Accessors.getConstructorAccessor(merchantRecipeListClass);
+					Class<?> craftMerchantRecipeClass = MinecraftReflection.getCraftBukkitClass("inventory.CraftMerchantRecipe");
+					FuzzyReflection reflection = FuzzyReflection.fromClass(craftMerchantRecipeClass, false);
+					bukkitMerchantRecipeToCraft = Accessors.getMethodAccessor(reflection.getMethodByName("fromBukkit"));
+					craftMerchantRecipeToNMS = Accessors.getMethodAccessor(reflection.getMethodByName("toMinecraft"));
+				}
+				return specific.stream().map(recipe -> craftMerchantRecipeToNMS.invoke(bukkitMerchantRecipeToCraft.invoke(null, recipe)))
+						.collect(() -> (List<Object>)merchantRecipeListConstructor.invoke(), List::add, List::addAll);
+			}
+			
+			@Override
+			public List<MerchantRecipe> getSpecific(Object generic) {
+				if (nmsMerchantRecipeToBukkit == null) {
+					Class<?> merchantRecipeClass = MinecraftReflection.getMinecraftClass("MerchantRecipe");
+					FuzzyReflection reflection = FuzzyReflection.fromClass(merchantRecipeClass, false);
+					nmsMerchantRecipeToBukkit = Accessors.getMethodAccessor(reflection.getMethodByName("asBukkit"));
+				}
+				return ((List<Object>)generic).stream().map(o -> (MerchantRecipe)nmsMerchantRecipeToBukkit.invoke(o)).collect(Collectors.toList());
+			}
+			
+			@Override
+			public Class<List<MerchantRecipe>> getSpecificType() {
+				// Damn you Java
+				Class<?> dummy = List.class;
+				return (Class<List<MerchantRecipe>>) dummy;
+			}
+			
+		});
+	}
+	
 }