/*
 * 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.HashMap;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;

/**
 * Multiset implementation backed by a {@link HashMap}.
 *
 * @author Kevin Bourrillion
 * @author Jared Levy
 * @since 2.0 (imported from Google Collections Library)
 */
@GwtCompatible(serializable = true, emulated = true)
public final class HashMultiset<E> extends AbstractMapBasedMultiset<E> {

	/**
	 * Creates a new, empty {@code HashMultiset} using the default initial capacity.
	 */
	public static <E> HashMultiset<E> create() {
		return new HashMultiset<E>();
	}

	/**
	 * Creates a new, empty {@code HashMultiset} with the specified expected number
	 * of distinct elements.
	 *
	 * @param distinctElements the expected number of distinct elements
	 * @throws IllegalArgumentException if {@code distinctElements} is negative
	 */
	public static <E> HashMultiset<E> create(int distinctElements) {
		return new HashMultiset<E>(distinctElements);
	}

	/**
	 * Creates a new {@code HashMultiset} containing the specified elements.
	 * 
	 * <p>
	 * This implementation is highly efficient when {@code elements} is itself a
	 * {@link Multiset}.
	 * 
	 * @param elements the elements that the multiset should contain
	 */
	public static <E> HashMultiset<E> create(Iterable<? extends E> elements) {
		HashMultiset<E> multiset = create(Multisets.inferDistinctElements(elements));
		Iterables.addAll(multiset, elements);
		return multiset;
	}

	private HashMultiset() {
		super(new HashMap<E, Count>());
	}

	private HashMultiset(int distinctElements) {
		super(Maps.<E, Count>newHashMapWithExpectedSize(distinctElements));
	}

	/**
	 * @serialData the number of distinct elements, the first element, its count,
	 *             the second element, its count, and so on
	 */
	@GwtIncompatible("java.io.ObjectOutputStream")
	private void writeObject(ObjectOutputStream stream) throws IOException {
		stream.defaultWriteObject();
		Serialization.writeMultiset(this, stream);
	}

	@GwtIncompatible("java.io.ObjectInputStream")
	private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException {
		stream.defaultReadObject();
		int distinctElements = Serialization.readCount(stream);
		setBackingMap(Maps.<E, Count>newHashMapWithExpectedSize(distinctElements));
		Serialization.populateMultiset(this, stream, distinctElements);
	}

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