ForgePatch/src/main/java/net/minecraftforge/fml/common/registry/ObjectHolderRef.java

package net.minecraftforge.fml.common.registry;

import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;

import net.minecraft.util.ResourceLocation;
import org.apache.logging.log4j.Level;

import com.google.common.base.Throwables;

import net.minecraft.block.Block;
import net.minecraft.init.Blocks;
import net.minecraft.item.Item;
import net.minecraftforge.fml.common.FMLLog;
import net.minecraftforge.fml.common.registry.GameRegistry.ObjectHolder;


/**
 * Internal class used in tracking {@link ObjectHolder} references
 *
 * @author cpw
 *
 */
class ObjectHolderRef {
    private Field field;
    private ResourceLocation injectedObject;
    private boolean isBlock;
    private boolean isItem;


    ObjectHolderRef(Field field, ResourceLocation injectedObject, boolean extractFromExistingValues)
    {
        this.field = field;
        this.isBlock = Block.class.isAssignableFrom(field.getType());
        this.isItem = Item.class.isAssignableFrom(field.getType());
        if (extractFromExistingValues)
        {
            try
            {
                Object existing = field.get(null);
                // nothing is ever allowed to replace AIR
                if (existing == null || existing == GameData.getBlockRegistry().getDefaultValue())
                {
                    this.injectedObject = null;
                    this.field = null;
                    this.isBlock = false;
                    this.isItem = false;
                    return;
                }
                else
                {
                    ResourceLocation tmp = isBlock ? ForgeRegistries.BLOCKS.getKey((Block)existing) :
                        isItem ? ForgeRegistries.ITEMS.getKey((Item)existing) : null;
                    this.injectedObject = tmp;
                }
            } catch (Exception e)
            {
                throw Throwables.propagate(e);
            }
        }
        else
        {
            this.injectedObject = injectedObject;
        }

        if (this.injectedObject == null || !isValid())
        {
            throw new IllegalStateException(String.format("The ObjectHolder annotation cannot apply to a field that is not an Item or Block (found : %s at %s.%s)", field.getType().getName(), field.getClass().getName(), field.getName()));
        }
        makeWritable(field);
    }

    private static Field modifiersField;
    private static Object reflectionFactory;
    private static Method newFieldAccessor;
    private static Method fieldAccessorSet;
    private static void makeWritable(Field f)
    {
        try
        {
            if (modifiersField == null)
            {
                Method getReflectionFactory = Class.forName("sun.reflect.ReflectionFactory").getDeclaredMethod("getReflectionFactory");
                reflectionFactory = getReflectionFactory.invoke(null);
                newFieldAccessor = Class.forName("sun.reflect.ReflectionFactory").getDeclaredMethod("newFieldAccessor", Field.class, boolean.class);
                fieldAccessorSet = Class.forName("sun.reflect.FieldAccessor").getDeclaredMethod("set", Object.class, Object.class);
                modifiersField = Field.class.getDeclaredField("modifiers");
                modifiersField.setAccessible(true);
            }
            modifiersField.setInt(f, f.getModifiers() & ~Modifier.FINAL);
        } catch (Exception e)
        {
            throw Throwables.propagate(e);
        }
    }

    public boolean isValid()
    {
        return isBlock || isItem;
    }
    public void apply()
    {
        Object thing;
        if (isBlock)
        {
            thing = ForgeRegistries.BLOCKS.getValue(injectedObject);
            if (thing == Blocks.AIR)
            {
                thing = null;
            }
        }
        else if (isItem)
        {
            thing = ForgeRegistries.ITEMS.getValue(injectedObject);
        }
        else
        {
            thing = null;
        }

        if (thing == null)
        {
            FMLLog.getLogger().log(Level.DEBUG, "Unable to lookup {} for {}. This means the object wasn't registered. It's likely just mod options.", injectedObject, field);
            return;
        }
        try
        {
            Object fieldAccessor = newFieldAccessor.invoke(reflectionFactory, field, false);
            fieldAccessorSet.invoke(fieldAccessor, null, thing);
        }
        catch (Exception e)
        {
            FMLLog.log(Level.WARN, e, "Unable to set %s with value %s (%s)", this.field, thing, this.injectedObject);
        }
    }
}