/*
 * 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 java.util.Map;
import java.util.Set;

import javax.annotation.Nullable;

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

/**
 * A map which forwards all its method calls to another map. Subclasses should
 * override one or more methods to modify the behavior of the backing map as
 * desired per the
 * <a href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator
 * pattern</a>.
 *
 * <p>
 * <i>Warning:</i> The methods of {@code ForwardingMap} forward
 * <i>indiscriminately</i> to the methods of the delegate. For example,
 * overriding {@link #put} alone <i>will not</i> change the behavior of
 * {@link #putAll}, which can lead to unexpected behavior. In this case, you
 * should override {@code putAll} as well, either providing your own
 * implementation, or delegating to the provided {@code standardPutAll} method.
 *
 * <p>
 * Each of the {@code standard} methods, where appropriate, use
 * {@link Objects#equal} to test equality for both keys and values. This may not
 * be the desired behavior for map implementations that use non-standard notions
 * of key equality, such as a {@code SortedMap} whose comparator is not
 * consistent with {@code equals}.
 *
 * <p>
 * The {@code standard} methods and the collection views they return are not
 * guaranteed to be thread-safe, even when all of the methods that they depend
 * on are thread-safe.
 *
 * @author Kevin Bourrillion
 * @author Jared Levy
 * @author Louis Wasserman
 * @since 2.0 (imported from Google Collections Library)
 */
@GwtCompatible
public abstract class ForwardingMap<K, V> extends ForwardingObject implements Map<K, V> {
	// TODO(user): identify places where thread safety is actually lost

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

	@Override
	protected abstract Map<K, V> delegate();

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

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

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

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

	@Override
	public boolean containsKey(@Nullable Object key) {
		return delegate().containsKey(key);
	}

	@Override
	public boolean containsValue(@Nullable Object value) {
		return delegate().containsValue(value);
	}

	@Override
	public V get(@Nullable Object key) {
		return delegate().get(key);
	}

	@Override
	public V put(K key, V value) {
		return delegate().put(key, value);
	}

	@Override
	public void putAll(Map<? extends K, ? extends V> map) {
		delegate().putAll(map);
	}

	@Override
	public Set<K> keySet() {
		return delegate().keySet();
	}

	@Override
	public Collection<V> values() {
		return delegate().values();
	}

	@Override
	public Set<Entry<K, V>> entrySet() {
		return delegate().entrySet();
	}

	@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 #putAll(Map)} in terms of
	 * {@link #put(Object, Object)}. If you override {@link #put(Object, Object)},
	 * you may wish to override {@link #putAll(Map)} to forward to this
	 * implementation.
	 *
	 * @since 7.0
	 */
	protected void standardPutAll(Map<? extends K, ? extends V> map) {
		Maps.putAllImpl(this, map);
	}

	/**
	 * A sensible, albeit inefficient, definition of {@link #remove} in terms of the
	 * {@code iterator} method of {@link #entrySet}. If you override
	 * {@link #entrySet}, you may wish to override {@link #remove} to forward to
	 * this implementation.
	 *
	 * <p>
	 * Alternately, you may wish to override {@link #remove} with {@code
	 * keySet().remove}, assuming that approach would not lead to an infinite loop.
	 *
	 * @since 7.0
	 */
	@Beta
	protected V standardRemove(@Nullable Object key) {
		Iterator<Entry<K, V>> entryIterator = entrySet().iterator();
		while (entryIterator.hasNext()) {
			Entry<K, V> entry = entryIterator.next();
			if (Objects.equal(entry.getKey(), key)) {
				V value = entry.getValue();
				entryIterator.remove();
				return value;
			}
		}
		return null;
	}

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

	/**
	 * A sensible implementation of {@link Map#keySet} in terms of the following
	 * methods: {@link ForwardingMap#clear}, {@link ForwardingMap#containsKey},
	 * {@link ForwardingMap#isEmpty}, {@link ForwardingMap#remove},
	 * {@link ForwardingMap#size}, and the {@link Set#iterator} method of
	 * {@link ForwardingMap#entrySet}. In many cases, you may wish to override
	 * {@link ForwardingMap#keySet} to forward to this implementation or a subclass
	 * thereof.
	 *
	 * @since 10.0
	 */
	@Beta
	protected class StandardKeySet extends Maps.KeySet<K, V> {
		/** Constructor for use by subclasses. */
		public StandardKeySet() {
			super(ForwardingMap.this);
		}
	}

	/**
	 * A sensible, albeit inefficient, definition of {@link #containsKey} in terms
	 * of the {@code iterator} method of {@link #entrySet}. If you override
	 * {@link #entrySet}, you may wish to override {@link #containsKey} to forward
	 * to this implementation.
	 *
	 * @since 7.0
	 */
	@Beta
	protected boolean standardContainsKey(@Nullable Object key) {
		return Maps.containsKeyImpl(this, key);
	}

	/**
	 * A sensible implementation of {@link Map#values} in terms of the following
	 * methods: {@link ForwardingMap#clear}, {@link ForwardingMap#containsValue},
	 * {@link ForwardingMap#isEmpty}, {@link ForwardingMap#size}, and the
	 * {@link Set#iterator} method of {@link ForwardingMap#entrySet}. In many cases,
	 * you may wish to override {@link ForwardingMap#values} to forward to this
	 * implementation or a subclass thereof.
	 *
	 * @since 10.0
	 */
	@Beta
	protected class StandardValues extends Maps.Values<K, V> {
		/** Constructor for use by subclasses. */
		public StandardValues() {
			super(ForwardingMap.this);
		}
	}

	/**
	 * A sensible definition of {@link #containsValue} in terms of the {@code
	 * iterator} method of {@link #entrySet}. If you override {@link #entrySet}, you
	 * may wish to override {@link #containsValue} to forward to this
	 * implementation.
	 *
	 * @since 7.0
	 */
	protected boolean standardContainsValue(@Nullable Object value) {
		return Maps.containsValueImpl(this, value);
	}

	/**
	 * A sensible implementation of {@link Map#entrySet} in terms of the following
	 * methods: {@link ForwardingMap#clear}, {@link ForwardingMap#containsKey},
	 * {@link ForwardingMap#get}, {@link ForwardingMap#isEmpty},
	 * {@link ForwardingMap#remove}, and {@link ForwardingMap#size}. In many cases,
	 * you may wish to override {@link #entrySet} to forward to this implementation
	 * or a subclass thereof.
	 *
	 * @since 10.0
	 */
	@Beta
	protected abstract class StandardEntrySet extends Maps.EntrySet<K, V> {
		/** Constructor for use by subclasses. */
		public StandardEntrySet() {
		}

		@Override
		Map<K, V> map() {
			return ForwardingMap.this;
		}
	}

	/**
	 * A sensible definition of {@link #isEmpty} in terms of the {@code iterator}
	 * method of {@link #entrySet}. If you override {@link #entrySet}, you may wish
	 * to override {@link #isEmpty} to forward to this implementation.
	 *
	 * @since 7.0
	 */
	protected boolean standardIsEmpty() {
		return !entrySet().iterator().hasNext();
	}

	/**
	 * A sensible definition of {@link #equals} in terms of the {@code equals}
	 * method of {@link #entrySet}. If you override {@link #entrySet}, you may wish
	 * to override {@link #equals} to forward to this implementation.
	 *
	 * @since 7.0
	 */
	protected boolean standardEquals(@Nullable Object object) {
		return Maps.equalsImpl(this, object);
	}

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

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