MinecraftForge/src/main/java/net/minecraftforge/registries/ObjectHolderRef.java

/*
 * Copyright (c) Forge Development LLC and contributors
 * SPDX-License-Identifier: LGPL-2.1-only
 */

package net.minecraftforge.registries;

import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.util.Locale;
import java.util.function.Consumer;
import java.util.function.Predicate;

import net.minecraft.resources.ResourceLocation;
import net.minecraft.ResourceLocationException;

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import org.jetbrains.annotations.Nullable;

@SuppressWarnings("rawtypes")
class ObjectHolderRef implements Consumer<Predicate<ResourceLocation>>, Runnable
{
    private static final Logger LOGGER  = LogManager.getLogger();
    private final Field field;
    private final ResourceLocation injectedObject;
    private final ForgeRegistry<?> registry;

    @SuppressWarnings("unchecked")
    @Nullable
    static ObjectHolderRef create(ResourceLocation registryName, Field field, String injectedObject, boolean extractFromExistingValues)
    {
        ForgeRegistry<?> registry = RegistryManager.ACTIVE.getRegistry(registryName);
        if (registry == null)
            return null;

        ResourceLocation injectedObjectName;
        if (extractFromExistingValues)
        {
            try
            {
                Object existing = field.get(null);
                // Nothing is ever allowed to replace AIR
                if (existing == null || existing == registry.getDefault())
                    return null;
                injectedObjectName = ((ForgeRegistry) registry).getKey(existing);
            }
            catch (IllegalAccessException e)
            {
                throw new RuntimeException(e);
            }
        }
        else
        {
            try
            {
                injectedObjectName = new ResourceLocation(injectedObject);
            }
            catch (ResourceLocationException e)
            {
                throw new IllegalArgumentException("Invalid @ObjectHolder annotation on \"" + field.toString() + "\"", e);
            }
        }

        if (injectedObjectName == null)
            throw new IllegalStateException(String.format(Locale.ENGLISH, "The ObjectHolder annotation cannot apply to a field that does not map to a registry. Ensure the registry was created during NewRegistryEvent. (found : %s at %s.%s)", field.getType().getName(), field.getDeclaringClass().getName(), field.getName()));

        field.setAccessible(true);

        if (Modifier.isFinal(field.getModifiers()))
        {
            throw new RuntimeException("@ObjectHolder on final field, our transformer did not run? " + field.getDeclaringClass().getName() + "/" + field.getName());
        }

        return new ObjectHolderRef(registry, field, injectedObjectName);
    }

    private ObjectHolderRef(ForgeRegistry<?> registry, Field field, ResourceLocation injectedObject)
    {
        this.registry = registry;
        this.field = field;
        this.injectedObject = injectedObject;
    }

    @Override
    public void accept(Predicate<ResourceLocation> filter)
    {
        if (registry == null || !filter.test(registry.getRegistryName()))
            return;
        run();
    }

    @Override
    public void run()
    {
        Object thing;
        if (registry.containsKey(injectedObject))
        {
            thing = registry.getValue(injectedObject);
        }
        else
        {
            thing = null;
        }

        if (thing == null)
        {
            LOGGER.debug("Unable to lookup {} for {}. This means the object wasn't registered. It's likely just mod options.", injectedObject, field);
            return;
        }
        try
        {
            field.set(null, thing);
        }
        catch (IllegalArgumentException | ReflectiveOperationException e)
        {
            LOGGER.warn("Unable to set {} with value {} ({})", this.field, thing, this.injectedObject, e);
        }
    }

    @Override
    public int hashCode()
    {
        return field.hashCode();
    }

    @Override
    public boolean equals(Object other)
    {
        if (!(other instanceof ObjectHolderRef))
            return false;
        ObjectHolderRef o = (ObjectHolderRef)other;
        return this.field.equals(o.field);
    }
}