*
 * @author James Sexton
 */
abstract class ForwardingGraph<N> extends AbstractGraph<N> {

  abstract BaseGraph<N> delegate();

  @Override
  public Set<N> nodes() {
    return delegate().nodes();
  }

  /**
   * Defer to {@link AbstractGraph#edges()} (based on {@link #successors(Object)}) for full edges()
   * implementation.
   */
  @Override

    implements ValueGraph<N, V> {
  /** Constructor for use by subclasses. */
  public AbstractValueGraph() {}

  @Override
  public Graph<N> asGraph() {
    return new AbstractGraph<N>() {
      @Override
      public Set<N> nodes() {
        return AbstractValueGraph.this.nodes();
      }

      @Override
      public Set<EndpointPair<N>> edges() {

      return EndpointPair.ordered(endpoints.target(), endpoints.source());
    }
    return endpoints;
  }

  // NOTE: this should work as long as the delegate graph's implementation of edges() (like that of
  // AbstractGraph) derives its behavior from calling successors().
  private static final class TransposedGraph<N> extends ForwardingGraph<N> {
    private final Graph<N> graph;

    TransposedGraph(Graph<N> graph) {

      return EndpointPair.ordered(endpoints.target(), endpoints.source());
    }
    return endpoints;
  }

  // NOTE: this should work as long as the delegate graph's implementation of edges() (like that of
  // AbstractGraph) derives its behavior from calling successors().
  private static final class TransposedGraph<N> extends ForwardingGraph<N> {
    private final Graph<N> graph;

    TransposedGraph(Graph<N> graph) {