/*
 * 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.VisibleForTesting;
import com.google.common.base.Preconditions;

import java.util.Collection;
import java.util.HashMap;
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);
  }
}

