/*
 * 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 java.util.Collection;
import java.util.Iterator;

import javax.annotation.Nullable;

import com.google.common.annotations.GwtCompatible;
import com.google.common.base.Objects;

/**
 * A collection which forwards all its method calls to another collection.
 * Subclasses should override one or more methods to modify the behavior of the
 * backing collection as desired per the
 * <a href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator
 * pattern</a>.
 *
 * <p>
 * <b>Warning:</b> The methods of {@code ForwardingCollection} 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 ForwardingCollection<E> extends ForwardingObject implements Collection<E> {
	// TODO(user): identify places where thread safety is actually lost

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

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

	@Override
	public Iterator<E> iterator() {
		return delegate().iterator();
	}

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

	@Override
	public boolean removeAll(Collection<?> collection) {
		return delegate().removeAll(collection);
	}

	@Override
	public boolean isEmpty() {
		return delegate().isEmpty();
	}

	@Override
	public boolean contains(Object object) {
		return delegate().contains(object);
	}

	@Override
	public boolean add(E element) {
		return delegate().add(element);
	}

	@Override
	public boolean remove(Object object) {
		return delegate().remove(object);
	}

	@Override
	public boolean containsAll(Collection<?> collection) {
		return delegate().containsAll(collection);
	}

	@Override
	public boolean addAll(Collection<? extends E> collection) {
		return delegate().addAll(collection);
	}

	@Override
	public boolean retainAll(Collection<?> collection) {
		return delegate().retainAll(collection);
	}

	@Override
	public void clear() {
		delegate().clear();
	}

	@Override
	public Object[] toArray() {
		return delegate().toArray();
	}

	@Override
	public <T> T[] toArray(T[] array) {
		return delegate().toArray(array);
	}

	/**
	 * A sensible definition of {@link #contains} in terms of {@link #iterator}. If
	 * you override {@link #iterator}, you may wish to override {@link #contains} to
	 * forward to this implementation.
	 *
	 * @since 7.0
	 */
	protected boolean standardContains(@Nullable Object object) {
		return Iterators.contains(iterator(), object);
	}

	/**
	 * A sensible definition of {@link #containsAll} in terms of {@link #contains} .
	 * If you override {@link #contains}, you may wish to override
	 * {@link #containsAll} to forward to this implementation.
	 *
	 * @since 7.0
	 */
	protected boolean standardContainsAll(Collection<?> collection) {
		return Collections2.containsAllImpl(this, collection);
	}

	/**
	 * A sensible definition of {@link #addAll} in terms of {@link #add}. If you
	 * override {@link #add}, you may wish to override {@link #addAll} to forward to
	 * this implementation.
	 *
	 * @since 7.0
	 */
	protected boolean standardAddAll(Collection<? extends E> collection) {
		return Iterators.addAll(this, collection.iterator());
	}

	/**
	 * A sensible definition of {@link #remove} in terms of {@link #iterator}, using
	 * the iterator's {@code remove} method. If you override {@link #iterator}, you
	 * may wish to override {@link #remove} to forward to this implementation.
	 *
	 * @since 7.0
	 */
	protected boolean standardRemove(@Nullable Object object) {
		Iterator<E> iterator = iterator();
		while (iterator.hasNext()) {
			if (Objects.equal(iterator.next(), object)) {
				iterator.remove();
				return true;
			}
		}
		return false;
	}

	/**
	 * A sensible definition of {@link #removeAll} in terms of {@link #iterator},
	 * using the iterator's {@code remove} method. If you override
	 * {@link #iterator}, you may wish to override {@link #removeAll} to forward to
	 * this implementation.
	 *
	 * @since 7.0
	 */
	protected boolean standardRemoveAll(Collection<?> collection) {
		return Iterators.removeAll(iterator(), collection);
	}

	/**
	 * A sensible definition of {@link #retainAll} in terms of {@link #iterator},
	 * using the iterator's {@code remove} method. If you override
	 * {@link #iterator}, you may wish to override {@link #retainAll} to forward to
	 * this implementation.
	 *
	 * @since 7.0
	 */
	protected boolean standardRetainAll(Collection<?> collection) {
		return Iterators.retainAll(iterator(), collection);
	}

	/**
	 * A sensible definition of {@link #clear} in terms of {@link #iterator}, using
	 * the iterator's {@code remove} method. If you override {@link #iterator}, you
	 * may wish to override {@link #clear} to forward to this implementation.
	 *
	 * @since 7.0
	 */
	protected void standardClear() {
		Iterators.clear(iterator());
	}

	/**
	 * A sensible definition of {@link #isEmpty} as {@code !iterator().hasNext}. If
	 * you override {@link #isEmpty}, you may wish to override {@link #isEmpty} to
	 * forward to this implementation. Alternately, it may be more efficient to
	 * implement {@code isEmpty} as {@code size() == 0}.
	 *
	 * @since 7.0
	 */
	protected boolean standardIsEmpty() {
		return !iterator().hasNext();
	}

	/**
	 * A sensible definition of {@link #toString} in terms of {@link #iterator}. If
	 * you override {@link #iterator}, you may wish to override {@link #toString} to
	 * forward to this implementation.
	 *
	 * @since 7.0
	 */
	protected String standardToString() {
		return Collections2.toStringImpl(this);
	}

	/**
	 * A sensible definition of {@link #toArray()} in terms of
	 * {@link #toArray(Object[])}. If you override {@link #toArray(Object[])}, you
	 * may wish to override {@link #toArray} to forward to this implementation.
	 *
	 * @since 7.0
	 */
	protected Object[] standardToArray() {
		Object[] newArray = new Object[size()];
		return toArray(newArray);
	}

	/**
	 * A sensible definition of {@link #toArray(Object[])} in terms of {@link #size}
	 * and {@link #iterator}. If you override either of these methods, you may wish
	 * to override {@link #toArray} to forward to this implementation.
	 *
	 * @since 7.0
	 */
	protected <T> T[] standardToArray(T[] array) {
		return ObjectArrays.toArrayImpl(this, array);
	}
}
