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/*
 * Copyright (c) 2008 Harold Cooper. All rights reserved.
 * Licensed under the MIT License.
 * See LICENSE file in the project root for full license information.
 */

package org.pcollections;

import java.io.Serializable;
import java.util.AbstractSet;
import java.util.Collection;
import java.util.Iterator;

/**
 * A map-backed persistent set.
 *
 * If the backing map is thread-safe, then this implementation is thread-safe (assuming Java's
 * AbstractSet is thread-safe), although its iterators may not be.
 *
 * @author harold
 * @param 
 */
public final class MapPSet extends AbstractSet implements PSet, Serializable {

  private static final long serialVersionUID = 1L;

  //// STATIC FACTORY METHODS ////
  /**
   * @param 
   * @param map
   * @return a PSet with the elements of map.keySet(), backed by map
   */
  @SuppressWarnings("unchecked")
  public static  MapPSet from(final PMap map) {
    return new MapPSet((PMap) map);
  }

  /**
   * @param 
   * @param map
   * @param e
   * @return from(map).plus(e)
   */
  public static  MapPSet from(final PMap map, E e) {
    return from(map).plus(e);
  }

  /**
   * @param 
   * @param map
   * @param list
   * @return from(map).plusAll(list)
   */
  public static  MapPSet from(final PMap map, final Collection list) {
    return from(map).plusAll(list);
  }

  //// PRIVATE CONSTRUCTORS ////
  private final PMap map;
  // not instantiable (or subclassable):
  private MapPSet(final PMap map) {
    this.map = map;
  }

  //// REQUIRED METHODS FROM AbstractSet ////
  @Override
  public Iterator iterator() {
    return map.keySet().iterator();
  }

  @Override
  public int size() {
    return map.size();
  }

  //// OVERRIDDEN METHODS OF AbstractSet ////
  @Override
  public boolean contains(final Object e) {
    return map.containsKey(e);
  }

  //// IMPLEMENTED METHODS OF PSet ////
  private static enum In {
    IN
  }

  public MapPSet plus(final E e) {
    if (contains(e)) return this;
    return new MapPSet(map.plus(e, In.IN));
  }

  public MapPSet minus(final Object e) {
    if (!contains(e)) return this;
    return new MapPSet(map.minus(e));
  }

  public MapPSet plusAll(final Collection list) {
    PMap map = this.map;
    for (E e : list) map = map.plus(e, In.IN);
    return from(map);
  }

  public MapPSet minusAll(final Collection list) {
    PMap map = this.map.minusAll(list);
    return from(map);
  }
}