/*
 * Copyright (C) 2007 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import static com.google.common.base.Preconditions.checkNotNull;

import java.util.Collection;
import java.util.Set;

import javax.annotation.Nullable;

import com.google.common.annotations.GwtCompatible;

/**
 * A set which forwards all its method calls to another set. Subclasses should
 * override one or more methods to modify the behavior of the backing set as
 * desired per the
 * <a href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator
 * pattern</a>.
 *
 * <p>
 * <b>Warning:</b> The methods of {@code ForwardingSet} forward
 * <b>indiscriminately</b> to the methods of the delegate. For example,
 * overriding {@link #add} alone <b>will not</b> change the behavior of
 * {@link #addAll}, which can lead to unexpected behavior. In this case, you
 * should override {@code addAll} as well, either providing your own
 * implementation, or delegating to the provided {@code standardAddAll} method.
 *
 * <p>
 * The {@code standard} methods are not guaranteed to be thread-safe, even when
 * all of the methods that they depend on are thread-safe.
 *
 * @author Kevin Bourrillion
 * @author Louis Wasserman
 * @since 2.0 (imported from Google Collections Library)
 */
@GwtCompatible
public abstract class ForwardingSet<E> extends ForwardingCollection<E> implements Set<E> {
	// TODO(user): identify places where thread safety is actually lost

	/** Constructor for use by subclasses. */
	protected ForwardingSet() {
	}

	@Override
	protected abstract Set<E> delegate();

	@Override
	public boolean equals(@Nullable Object object) {
		return object == this || delegate().equals(object);
	}

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

	/**
	 * A sensible definition of {@link #removeAll} in terms of {@link #iterator} and
	 * {@link #remove}. If you override {@code iterator} or {@code remove}, you may
	 * wish to override {@link #removeAll} to forward to this implementation.
	 *
	 * @since 7.0 (this version overrides the {@code ForwardingCollection} version
	 *        as of 12.0)
	 */
	@Override
	protected boolean standardRemoveAll(Collection<?> collection) {
		return Sets.removeAllImpl(this, checkNotNull(collection)); // for GWT
	}

	/**
	 * A sensible definition of {@link #equals} in terms of {@link #size} and
	 * {@link #containsAll}. If you override either of those methods, you may wish
	 * to override {@link #equals} to forward to this implementation.
	 *
	 * @since 7.0
	 */
	protected boolean standardEquals(@Nullable Object object) {
		return Sets.equalsImpl(this, object);
	}

	/**
	 * A sensible definition of {@link #hashCode} in terms of {@link #iterator}. If
	 * you override {@link #iterator}, you may wish to override {@link #equals} to
	 * forward to this implementation.
	 *
	 * @since 7.0
	 */
	protected int standardHashCode() {
		return Sets.hashCodeImpl(this);
	}
}