/*
 * 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 com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Preconditions;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.Collection;
import java.util.Map;
import java.util.Set;

Implementation of Multimap using hash tables. 
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.
Keys and values may be null. All optional multimap methods are supported, and all returned
views are modifiable.
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 Multimaps.synchronizedSetMultimap. 
Author:
Jared Levy
Since:
2.0/**
 * 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
 */
@GwtCompatible(serializable = true, emulated = true)
public final class HashMultimap<K, V> extends HashMultimapGwtSerializationDependencies<K, V> {
  private static final int DEFAULT_VALUES_PER_KEY = 2;

  @VisibleForTesting transient int expectedValuesPerKey = DEFAULT_VALUES_PER_KEY;

  
Creates a new, empty HashMultimap with the default initial capacities. 
This method will soon be deprecated in favor of 
MultimapBuilder.hashKeys().hashSetValues().build(). /**
   * Creates a new, empty {@code HashMultimap} with the default initial capacities.
   *
   * <p>This method will soon be deprecated in favor of {@code
   * MultimapBuilder.hashKeys().hashSetValues().build()}.
   */
  public static <K, V> HashMultimap<K, V> create() {
    return new HashMultimap<>();
  }

  
Constructs an empty HashMultimap with enough capacity to hold the specified numbers of keys and values without rehashing. 
This method will soon be deprecated in favor of 
MultimapBuilder.hashKeys(expectedKeys).hashSetValues(expectedValuesPerKey).build(). 
Params:
expectedKeys – the expected number of distinct keys
expectedValuesPerKey – the expected average number of values per key
Throws:
IllegalArgumentException – if expectedKeys or expectedValuesPerKey is negative/**
   * Constructs an empty {@code HashMultimap} with enough capacity to hold the specified numbers of
   * keys and values without rehashing.
   *
   * <p>This method will soon be deprecated in favor of {@code
   * MultimapBuilder.hashKeys(expectedKeys).hashSetValues(expectedValuesPerKey).build()}.
   *
   * @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<>(expectedKeys, expectedValuesPerKey);
  }

  
Constructs a 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. 
This method will soon be deprecated in favor of 
MultimapBuilder.hashKeys().hashSetValues().build(multimap). 
Params:
multimap – the multimap whose contents are copied to this multimap/**
   * 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.
   *
   * <p>This method will soon be deprecated in favor of {@code
   * MultimapBuilder.hashKeys().hashSetValues().build(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<>(multimap);
  }

  private HashMultimap() {
    this(12, DEFAULT_VALUES_PER_KEY);
  }

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

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

  
{@inheritDoc}
Creates an empty HashSet for a collection of values for one key. 
Returns:
a new HashSet containing a collection of values for one key/**
   * {@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 Platform.<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/**
   * @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();
    Serialization.writeMultimap(this, stream);
  }

  @GwtIncompatible // java.io.ObjectInputStream
  private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException {
    stream.defaultReadObject();
    expectedValuesPerKey = DEFAULT_VALUES_PER_KEY;
    int distinctKeys = Serialization.readCount(stream);
    Map<K, Collection<V>> map = Platform.newHashMapWithExpectedSize(12);
    setMap(map);
    Serialization.populateMultimap(this, stream, distinctKeys);
  }

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