MinecraftForge/src/main/java/net/minecraftforge/fml/RegistryObject.java

/*
 * Minecraft Forge
 * Copyright (c) 2016-2021.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation version 2.1
 * of the License.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 */

package net.minecraftforge.fml;

import net.minecraft.util.ResourceLocation;
import net.minecraftforge.registries.IForgeRegistry;
import net.minecraftforge.registries.IForgeRegistryEntry;
import net.minecraftforge.registries.ObjectHolderRegistry;
import net.minecraftforge.registries.RegistryManager;

import javax.annotation.Nonnull;
import javax.annotation.Nullable;

import java.util.Objects;
import java.util.Optional;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.function.Supplier;
import java.util.stream.Stream;

public final class RegistryObject<T extends IForgeRegistryEntry<? super T>> implements Supplier<T>
{
    private final ResourceLocation name;
    @Nullable
    private T value;

    public static <T extends IForgeRegistryEntry<T>, U extends T> RegistryObject<U> of(final ResourceLocation name, Supplier<Class<? super T>> registryType) {
        return new RegistryObject<>(name, registryType);
    }

    public static <T extends IForgeRegistryEntry<T>, U extends T> RegistryObject<U> of(final ResourceLocation name, IForgeRegistry<T> registry) {
        return new RegistryObject<>(name, registry);
    }

    public static <T extends IForgeRegistryEntry<T>, U extends T> RegistryObject<U> of(final ResourceLocation name, final Class<T> baseType, String modid) {
        return new RegistryObject<>(name, baseType, modid);
    }

    private static RegistryObject<?> EMPTY = new RegistryObject<>();

    private static <T extends IForgeRegistryEntry<? super T>> RegistryObject<T> empty() {
        @SuppressWarnings("unchecked")
        RegistryObject<T> t = (RegistryObject<T>) EMPTY;
        return t;
    }

    private RegistryObject() {
        this.name = null;
    }

    private <V extends IForgeRegistryEntry<V>> RegistryObject(ResourceLocation name, Supplier<Class<? super V>> registryType)
    {
        this(name, RegistryManager.ACTIVE.<V>getRegistry(registryType.get()));
    }

    @SuppressWarnings("unchecked")
    private <V extends IForgeRegistryEntry<V>> RegistryObject(ResourceLocation name, IForgeRegistry<V> registry)
    {
        if (registry == null)
            throw new IllegalArgumentException("Invalid registry argument, must not be null");
        this.name = name;
        ObjectHolderRegistry.addHandler(pred ->
        {
            if (pred.test(registry.getRegistryName()))
                this.value = registry.containsKey(this.name) ? (T)registry.getValue(this.name) : null;
        });
    }

    @SuppressWarnings("unchecked")
    private <V extends IForgeRegistryEntry<V>> RegistryObject(final ResourceLocation name, final Class<V> baseType, final String modid)
    {
        this.name = name;
        final Throwable callerStack = new Throwable("Calling Site from mod: " + modid);
        ObjectHolderRegistry.addHandler(new Consumer<Predicate<ResourceLocation>>()
        {
            private IForgeRegistry<V> registry;

            @Override
            public void accept(Predicate<ResourceLocation> pred)
            {
                if (registry == null)
                {
                    this.registry = RegistryManager.ACTIVE.getRegistry(baseType);
                    if (registry == null)
                        throw new IllegalStateException("Unable to find registry for type " + baseType.getName() + " for mod \"" + modid + "\". Check the 'caused by' to see futher stack.", callerStack);
                }
                if (pred.test(registry.getRegistryName()))
                    RegistryObject.this.value = registry.containsKey(RegistryObject.this.name) ? (T)registry.getValue(RegistryObject.this.name) : null;
            }
        });
    }

    /**
     * Directly retrieves the wrapped Registry Object. This value will automatically be updated when the backing registry is updated.
     * Will throw NPE if the value is null, use isPresent to check first. Or use any of the other guarded functions.
     */
    @Override
    @Nonnull
    public T get()
    {
        T ret = this.value;
        Objects.requireNonNull(ret, () -> "Registry Object not present: " + this.name);
        return ret;
    }

    public void updateReference(IForgeRegistry<? extends T> registry)
    {
        this.value = registry.getValue(getId());
    }

    public ResourceLocation getId()
    {
        return this.name;
    }

    public Stream<T> stream() {
        return isPresent() ? Stream.of(get()) : Stream.of();
    }

    /**
     * Return {@code true} if there is a mod object present, otherwise {@code false}.
     *
     * @return {@code true} if there is a mod object present, otherwise {@code false}
     */
    public boolean isPresent() {
        return this.value != null;
    }

    /**
     * If a mod object is present, invoke the specified consumer with the object,
     * otherwise do nothing.
     *
     * @param consumer block to be executed if a mod object is present
     * @throws NullPointerException if mod object is present and {@code consumer} is
     * null
     */
    public void ifPresent(Consumer<? super T> consumer) {
        if (isPresent())
            consumer.accept(get());
    }

    /**
     * If a mod object is present, and the mod object matches the given predicate,
     * return an {@code RegistryObject} describing the value, otherwise return an
     * empty {@code RegistryObject}.
     *
     * @param predicate a predicate to apply to the mod object, if present
     * @return an {@code RegistryObject} describing the value of this {@code RegistryObject}
     * if a mod object is present and the mod object matches the given predicate,
     * otherwise an empty {@code RegistryObject}
     * @throws NullPointerException if the predicate is null
     */
    public RegistryObject<T> filter(Predicate<? super T> predicate) {
        Objects.requireNonNull(predicate);
        if (!isPresent())
            return this;
        else
            return predicate.test(get()) ? this : empty();
    }

    /**
     * If a mod object is present, apply the provided mapping function to it,
     * and if the result is non-null, return an {@code Optional} describing the
     * result.  Otherwise return an empty {@code Optional}.
     *
     * @apiNote This method supports post-processing on optional values, without
     * the need to explicitly check for a return status.
     *
     * @param <U> The type of the result of the mapping function
     * @param mapper a mapping function to apply to the mod object, if present
     * @return an {@code Optional} describing the result of applying a mapping
     * function to the mod object of this {@code RegistryObject}, if a mod object is present,
     * otherwise an empty {@code Optional}
     * @throws NullPointerException if the mapping function is null
     */
    public<U> Optional<U> map(Function<? super T, ? extends U> mapper) {
        Objects.requireNonNull(mapper);
        if (!isPresent())
            return Optional.empty();
        else {
            return Optional.ofNullable(mapper.apply(get()));
        }
    }

    /**
     * If a value is present, apply the provided {@code Optional}-bearing
     * mapping function to it, return that result, otherwise return an empty
     * {@code Optional}.  This method is similar to {@link #map(Function)},
     * but the provided mapper is one whose result is already an {@code Optional},
     * and if invoked, {@code flatMap} does not wrap it with an additional
     * {@code Optional}.
     *
     * @param <U> The type parameter to the {@code Optional} returned by
     * @param mapper a mapping function to apply to the mod object, if present
     *           the mapping function
     * @return the result of applying an {@code Optional}-bearing mapping
     * function to the value of this {@code Optional}, if a value is present,
     * otherwise an empty {@code Optional}
     * @throws NullPointerException if the mapping function is null or returns
     * a null result
     */
    public<U> Optional<U> flatMap(Function<? super T, Optional<U>> mapper) {
        Objects.requireNonNull(mapper);
        if (!isPresent())
            return Optional.empty();
        else {
            return Objects.requireNonNull(mapper.apply(get()));
        }
    }

    /**
     * If a mod object is present, lazily apply the provided mapping function to it,
     * returning a supplier for the transformed result. If this object is empty, or the
     * mapping function returns {@code null}, the supplier will return {@code null}.
     *
     * @apiNote This method supports post-processing on optional values, without
     * the need to explicitly check for a return status.
     *
     * @param <U> The type of the result of the mapping function
     * @param mapper A mapping function to apply to the mod object, if present
     * @return A {@code Supplier} lazily providing the result of applying a mapping
     * function to the mod object of this {@code RegistryObject}, if a mod object is present,
     * otherwise a supplier returning {@code null}
     * @throws NullPointerException if the mapping function is {@code null}
     */
    public<U> Supplier<U> lazyMap(Function<? super T, ? extends U> mapper) {
        Objects.requireNonNull(mapper);
        return () -> isPresent() ? mapper.apply(get()) : null;
    }

    /**
     * Return the mod object if present, otherwise return {@code other}.
     *
     * @param other the mod object to be returned if there is no mod object present, may
     * be null
     * @return the mod object, if present, otherwise {@code other}
     */
    public T orElse(T other) {
        return isPresent() ? get() : other;
    }

    /**
     * Return the mod object if present, otherwise invoke {@code other} and return
     * the result of that invocation.
     *
     * @param other a {@code Supplier} whose result is returned if no mod object
     * is present
     * @return the mod object if present otherwise the result of {@code other.get()}
     * @throws NullPointerException if mod object is not present and {@code other} is
     * null
     */
    public T orElseGet(Supplier<? extends T> other) {
        return isPresent() ? get() : other.get();
    }

    /**
     * Return the contained mod object, if present, otherwise throw an exception
     * to be created by the provided supplier.
     *
     * @apiNote A method reference to the exception constructor with an empty
     * argument list can be used as the supplier. For example,
     * {@code IllegalStateException::new}
     *
     * @param <X> Type of the exception to be thrown
     * @param exceptionSupplier The supplier which will return the exception to
     * be thrown
     * @return the present mod object
     * @throws X if there is no mod object present
     * @throws NullPointerException if no mod object is present and
     * {@code exceptionSupplier} is null
     */
    public <X extends Throwable> T orElseThrow(Supplier<? extends X> exceptionSupplier) throws X {
        if (isPresent()) {
            return get();
        } else {
            throw exceptionSupplier.get();
        }
    }

    @Override
    public boolean equals(Object obj)
    {
        if (this == obj) return true;
        if (obj instanceof RegistryObject) {
            return Objects.equals(((RegistryObject<?>)obj).name, name);
        }
        return false;
    }

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