/*
    * Created on Oct 18, 2005
    *
    * Copyright (c) 2005, The JUNG Authors 
    *
    * All rights reserved.
    *
    * This software is open-source under the BSD license; see either
    * "license.txt" or
   * https://github.com/jrtom/jung/blob/master/LICENSE 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 com.google.common.base.Supplier;
  
  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> {
  	
      /**
       * @param <V> the vertex type for the graph Supplier
       * @param <E> the edge type for the graph Supplier
       * @return a {@code Supplier} that creates an instance of this graph type.
       */
  	public static <V,E> Supplier<UndirectedGraph<V,E>> getFactory() {
  		return new Supplier<UndirectedGraph<V,E>> () {
  			public UndirectedGraph<V,E> get() {
  				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);
      }
  }