/*
    * Licensed to the Apache Software Foundation (ASF) under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * The ASF licenses this file to You 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 org.apache.commons.collections4.set;
  
  import java.io.Serializable;
  import java.util.Collection;
  import java.util.Iterator;
  import java.util.Map;
  import java.util.Objects;
  import java.util.Set;
  import java.util.function.Predicate;
  
  /**
   * Decorates a {@code Map} to obtain {@code Set} behavior.
   * <p>
   * This class is used to create a {@code Set} with the same properties as
   * the key set of any map. Thus, a ReferenceSet can be created by wrapping a
   * {@code ReferenceMap} in an instance of this class.
   * </p>
   * <p>
   * Most map implementation can be used to create a set by passing in dummy values.
   * Exceptions include {@code BidiMap} implementations, as they require unique values.
   * </p>
   *
   * @param <E> the type of the elements in this set
   * @param <V> the dummy value type in this map
   * @since 3.1
   */
  public final class MapBackedSet<E, V> implements Set<E>, Serializable {
  
      /** Serialization version */
      private static final long serialVersionUID = 6723912213766056587L;
  
      /**
       * Factory method to create a set from a map.
       *
       * @param <E> the element type
       * @param <V> the dummy value type in the map
       * @param map  the map to decorate, must not be null
       * @return a new map backed set
       * @throws NullPointerException if map is null
       * @since 4.0
       */
      public static <E, V> MapBackedSet<E, V> mapBackedSet(final Map<E, ? super V> map) {
          return mapBackedSet(map, null);
      }
  
      /**
       * Factory method to create a set from a map.
       *
       * @param <E> the element type
       * @param <V> the dummy value type in the map
       * @param map  the map to decorate, must not be null
       * @param dummyValue  the dummy value to use
       * @return a new map backed set
       * @throws NullPointerException if map is null
       * @since 4.0
       */
      public static <E, V> MapBackedSet<E, V> mapBackedSet(final Map<E, ? super V> map, final V dummyValue) {
          return new MapBackedSet<>(map, dummyValue);
      }
  
      /** The map being used as the backing store */
      private final Map<E, ? super V> map;
  
      /** The dummyValue to use */
      private final V dummyValue;
  
      /**
       * Constructor that wraps (not copies).
       *
       * @param map  the map to decorate, must not be null
       * @param dummyValue  the dummy value to use
       * @throws NullPointerException if map is null
       */
      private MapBackedSet(final Map<E, ? super V> map, final V dummyValue) {
          this.map = Objects.requireNonNull(map, "map");
          this.dummyValue = dummyValue;
      }
  
      @Override
      public boolean add(final E obj) {
          final int size = map.size();
          map.put(obj, dummyValue);
          return map.size() != size;
     }
 
     @Override
     public boolean addAll(final Collection<? extends E> coll) {
         final int size = map.size();
         for (final E e : coll) {
             map.put(e, dummyValue);
         }
         return map.size() != size;
     }
 
     @Override
     public void clear() {
         map.clear();
     }
 
     @Override
     public boolean contains(final Object obj) {
         return map.containsKey(obj);
     }
 
     @Override
     public boolean containsAll(final Collection<?> coll) {
         return map.keySet().containsAll(coll);
     }
 
     @Override
     public boolean equals(final Object obj) {
         return map.keySet().equals(obj);
     }
 
     @Override
     public int hashCode() {
         return map.keySet().hashCode();
     }
 
     @Override
     public boolean isEmpty() {
         return map.isEmpty();
     }
 
     @Override
     public Iterator<E> iterator() {
         return map.keySet().iterator();
     }
 
     @Override
     public boolean remove(final Object obj) {
         final int size = map.size();
         map.remove(obj);
         return map.size() != size;
     }
 
     @Override
     public boolean removeAll(final Collection<?> coll) {
         return map.keySet().removeAll(coll);
     }
 
     /**
      * @since 4.4
      */
     @Override
     public boolean removeIf(final Predicate<? super E> filter) {
         return map.keySet().removeIf(filter);
     }
 
     @Override
     public boolean retainAll(final Collection<?> coll) {
         return map.keySet().retainAll(coll);
     }
 
     @Override
     public int size() {
         return map.size();
     }
 
     @Override
     public Object[] toArray() {
         return map.keySet().toArray();
     }
 
     @Override
     public <T> T[] toArray(final T[] array) {
         return map.keySet().toArray(array);
     }
 
 }