/*
 * 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.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.Collection;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Preconditions;

/**
 * Implementation of {@link Multimap} using hash tables.
 *
 * <p>
 * The multimap does not store duplicate key-value pairs. Adding a new key-value
 * pair equal to an existing key-value pair has no effect.
 *
 * <p>
 * Keys and values may be null. All optional multimap methods are supported, and
 * all returned views are modifiable.
 *
 * <p>
 * This class is not threadsafe when any concurrent operations update the
 * multimap. Concurrent read operations will work correctly. To allow concurrent
 * update operations, wrap your multimap with a call to
 * {@link Multimaps#synchronizedSetMultimap}.
 *
 * @author Jared Levy
 * @since 2.0 (imported from Google Collections Library)
 */
@GwtCompatible(serializable = true, emulated = true)
public final class HashMultimap<K, V> extends AbstractSetMultimap<K, V> {
	private static final int DEFAULT_VALUES_PER_KEY = 2;

	@VisibleForTesting
	transient int expectedValuesPerKey = DEFAULT_VALUES_PER_KEY;

	/**
	 * Creates a new, empty {@code HashMultimap} with the default initial
	 * capacities.
	 */
	public static <K, V> HashMultimap<K, V> create() {
		return new HashMultimap<K, V>();
	}

	/**
	 * Constructs an empty {@code HashMultimap} with enough capacity to hold the
	 * specified numbers of keys and values without rehashing.
	 *
	 * @param expectedKeys         the expected number of distinct keys
	 * @param expectedValuesPerKey the expected average number of values per key
	 * @throws IllegalArgumentException if {@code expectedKeys} or {@code
	 *      expectedValuesPerKey}    is negative
	 */
	public static <K, V> HashMultimap<K, V> create(int expectedKeys, int expectedValuesPerKey) {
		return new HashMultimap<K, V>(expectedKeys, expectedValuesPerKey);
	}

	/**
	 * Constructs a {@code HashMultimap} with the same mappings as the specified
	 * multimap. If a key-value mapping appears multiple times in the input
	 * multimap, it only appears once in the constructed multimap.
	 *
	 * @param multimap the multimap whose contents are copied to this multimap
	 */
	public static <K, V> HashMultimap<K, V> create(Multimap<? extends K, ? extends V> multimap) {
		return new HashMultimap<K, V>(multimap);
	}

	private HashMultimap() {
		super(new HashMap<K, Collection<V>>());
	}

	private HashMultimap(int expectedKeys, int expectedValuesPerKey) {
		super(Maps.<K, Collection<V>>newHashMapWithExpectedSize(expectedKeys));
		Preconditions.checkArgument(expectedValuesPerKey >= 0);
		this.expectedValuesPerKey = expectedValuesPerKey;
	}

	private HashMultimap(Multimap<? extends K, ? extends V> multimap) {
		super(Maps.<K, Collection<V>>newHashMapWithExpectedSize(multimap.keySet().size()));
		putAll(multimap);
	}

	/**
	 * {@inheritDoc}
	 *
	 * <p>
	 * Creates an empty {@code HashSet} for a collection of values for one key.
	 *
	 * @return a new {@code HashSet} containing a collection of values for one key
	 */
	@Override
	Set<V> createCollection() {
		return Sets.<V>newHashSetWithExpectedSize(expectedValuesPerKey);
	}

	/**
	 * @serialData expectedValuesPerKey, number of distinct keys, and then for each
	 *             distinct key: the key, number of values for that key, and the
	 *             key's values
	 */
	@GwtIncompatible("java.io.ObjectOutputStream")
	private void writeObject(ObjectOutputStream stream) throws IOException {
		stream.defaultWriteObject();
		stream.writeInt(expectedValuesPerKey);
		Serialization.writeMultimap(this, stream);
	}

	@GwtIncompatible("java.io.ObjectInputStream")
	private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException {
		stream.defaultReadObject();
		expectedValuesPerKey = stream.readInt();
		int distinctKeys = Serialization.readCount(stream);
		Map<K, Collection<V>> map = Maps.newHashMapWithExpectedSize(distinctKeys);
		setMap(map);
		Serialization.populateMultimap(this, stream, distinctKeys);
	}

	@GwtIncompatible("Not needed in emulated source")
	private static final long serialVersionUID = 0;
}
