/*

  * Created on Oct 18, 2005

  *

  * Copyright (c) 2005, the JUNG Project and the Regents of the University 

  * of California

  * All rights reserved.

  *

  * This software is open-source under the BSD license; see either

  * "license.txt" or

  * http://jung.sourceforge.net/license.txt for a description.

  */

 package edu.uci.ics.jung.graph;

 import java.util.Collection;

 import java.util.Collections;

 import java.util.LinkedHashMap;

 import java.util.LinkedHashSet;

 import java.util.Set;

 import org.apache.commons.collections15.Factory;

 import edu.uci.ics.jung.graph.util.Pair;

 /**

  * An implementation of <code>UndirectedGraph</code> that is suitable for sparse graphs,

  * orders its vertex and edge collections according to insertion time, and permits

  * parallel edges.

  */

 @SuppressWarnings("serial")

 public class UndirectedOrderedSparseMultigraph<V,E> 

     extends UndirectedSparseMultigraph<V,E>

     implements UndirectedGraph<V,E> {

     /**

      * Returns a {@code Factory} that creates an instance of this graph type.

      * @param <V> the vertex type for the graph factory

      * @param <E> the edge type for the graph factory

      */

         public static <V,E> Factory<UndirectedGraph<V,E>> getFactory() {

                 return new Factory<UndirectedGraph<V,E>> () {

                         public UndirectedGraph<V,E> create() {

                                 return new UndirectedOrderedSparseMultigraph<V,E>();

                         }

                 };

         }

         /**

          * Creates a new instance.

          */

     public UndirectedOrderedSparseMultigraph() {

         vertices = new LinkedHashMap<V, Set<E>>();

         edges = new LinkedHashMap<E, Pair<V>>();

     }

     @Override

     public boolean addVertex(V vertex) {

             if(vertex == null) {

                     throw new IllegalArgumentException("vertex may not be null");

             }

         if (!containsVertex(vertex))

         {

             vertices.put(vertex, new LinkedHashSet<E>());

             return true;

         } else {

             return false;

         }

     }

     @Override

     public Collection<V> getNeighbors(V vertex) {

         if (!containsVertex(vertex))

             return null;

         Set<V> neighbors = new LinkedHashSet<V>();

         for (E edge : getIncident_internal(vertex))

         {

             Pair<V> endpoints = this.getEndpoints(edge);

             V e_a = endpoints.getFirst();

             V e_b = endpoints.getSecond();

             if (vertex.equals(e_a))

                 neighbors.add(e_b);

             else

                 neighbors.add(e_a);

         }

         return Collections.unmodifiableCollection(neighbors);

     }

 }