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