/*
 * Copyright (C) 2012 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.AbstractCollection;
import java.util.Collection;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;

import javax.annotation.Nullable;

import com.google.common.annotations.GwtCompatible;

/**
 * A skeleton {@code Multimap} implementation, not necessarily in terms of a
 * {@code Map}.
 * 
 * @author Louis Wasserman
 */
@GwtCompatible
abstract class AbstractMultimap<K, V> implements Multimap<K, V> {
	@Override
	public boolean isEmpty() {
		return size() == 0;
	}

	@Override
	public boolean containsValue(@Nullable Object value) {
		for (Collection<V> collection : asMap().values()) {
			if (collection.contains(value)) {
				return true;
			}
		}

		return false;
	}

	@Override
	public boolean containsEntry(@Nullable Object key, @Nullable Object value) {
		Collection<V> collection = asMap().get(key);
		return collection != null && collection.contains(value);
	}

	@Override
	public boolean remove(@Nullable Object key, @Nullable Object value) {
		Collection<V> collection = asMap().get(key);
		return collection != null && collection.remove(value);
	}

	@Override
	public boolean put(@Nullable K key, @Nullable V value) {
		return get(key).add(value);
	}

	@Override
	public boolean putAll(@Nullable K key, Iterable<? extends V> values) {
		checkNotNull(values);
		// make sure we only call values.iterator() once
		// and we only call get(key) if values is nonempty
		if (values instanceof Collection) {
			Collection<? extends V> valueCollection = (Collection<? extends V>) values;
			return !valueCollection.isEmpty() && get(key).addAll(valueCollection);
		} else {
			Iterator<? extends V> valueItr = values.iterator();
			return valueItr.hasNext() && Iterators.addAll(get(key), valueItr);
		}
	}

	@Override
	public boolean putAll(Multimap<? extends K, ? extends V> multimap) {
		boolean changed = false;
		for (Map.Entry<? extends K, ? extends V> entry : multimap.entries()) {
			changed |= put(entry.getKey(), entry.getValue());
		}
		return changed;
	}

	@Override
	public Collection<V> replaceValues(@Nullable K key, Iterable<? extends V> values) {
		checkNotNull(values);
		Collection<V> result = removeAll(key);
		putAll(key, values);
		return result;
	}

	private transient Collection<Entry<K, V>> entries;

	@Override
	public Collection<Entry<K, V>> entries() {
		Collection<Entry<K, V>> result = entries;
		return (result == null) ? entries = createEntries() : result;
	}

	Collection<Entry<K, V>> createEntries() {
		if (this instanceof SetMultimap) {
			return new EntrySet();
		} else {
			return new Entries();
		}
	}

	private class Entries extends Multimaps.Entries<K, V> {
		@Override
		Multimap<K, V> multimap() {
			return AbstractMultimap.this;
		}

		@Override
		public Iterator<Entry<K, V>> iterator() {
			return entryIterator();
		}
	}

	private class EntrySet extends Entries implements Set<Entry<K, V>> {
		@Override
		public int hashCode() {
			return Sets.hashCodeImpl(this);
		}

		@Override
		public boolean equals(@Nullable Object obj) {
			return Sets.equalsImpl(this, obj);
		}
	}

	abstract Iterator<Entry<K, V>> entryIterator();

	private transient Set<K> keySet;

	@Override
	public Set<K> keySet() {
		Set<K> result = keySet;
		return (result == null) ? keySet = createKeySet() : result;
	}

	Set<K> createKeySet() {
		return new Maps.KeySet<K, Collection<V>>(asMap());
	}

	private transient Multiset<K> keys;

	@Override
	public Multiset<K> keys() {
		Multiset<K> result = keys;
		return (result == null) ? keys = createKeys() : result;
	}

	Multiset<K> createKeys() {
		return new Multimaps.Keys<K, V>(this);
	}

	private transient Collection<V> values;

	@Override
	public Collection<V> values() {
		Collection<V> result = values;
		return (result == null) ? values = createValues() : result;
	}

	Collection<V> createValues() {
		return new Values();
	}

	class Values extends AbstractCollection<V> {
		@Override
		public Iterator<V> iterator() {
			return valueIterator();
		}

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

		@Override
		public boolean contains(@Nullable Object o) {
			return AbstractMultimap.this.containsValue(o);
		}

		@Override
		public void clear() {
			AbstractMultimap.this.clear();
		}
	}

	Iterator<V> valueIterator() {
		return Maps.valueIterator(entries().iterator());
	}

	private transient Map<K, Collection<V>> asMap;

	@Override
	public Map<K, Collection<V>> asMap() {
		Map<K, Collection<V>> result = asMap;
		return (result == null) ? asMap = createAsMap() : result;
	}

	abstract Map<K, Collection<V>> createAsMap();

	// Comparison and hashing

	@Override
	public boolean equals(@Nullable Object object) {
		return Multimaps.equalsImpl(this, object);
	}

	/**
	 * Returns the hash code for this multimap.
	 *
	 * <p>
	 * The hash code of a multimap is defined as the hash code of the map view, as
	 * returned by {@link Multimap#asMap}.
	 *
	 * @see Map#hashCode
	 */
	@Override
	public int hashCode() {
		return asMap().hashCode();
	}

	/**
	 * Returns a string representation of the multimap, generated by calling
	 * {@code toString} on the map returned by {@link Multimap#asMap}.
	 *
	 * @return a string representation of the multimap
	 */
	@Override
	public String toString() {
		return asMap().toString();
	}
}
