*
 * @author James Sexton
 * @param <E> Edge parameter type
 */
@ElementTypesAreNonnullByDefault
final class EdgesConnecting<E> extends AbstractSet<E> {

  private final Map<?, E> nodeToOutEdge;
  private final Object targetNode;

  EdgesConnecting(Map<?, E> nodeToEdgeMap, Object targetNode) {
    this.nodeToOutEdge = checkNotNull(nodeToEdgeMap);
    this.targetNode = checkNotNull(targetNode);
  }

    assertThat(network.edgesConnecting("B", "A")).isEmpty();
  }

  @Test
  public void edgesConnecting_undirected() {
    MutableNetwork<String, String> mutableNetwork =
        NetworkBuilder.undirected().allowsSelfLoops(true).build();
    mutableNetwork.addEdge("A", "A", "AA");
    mutableNetwork.addEdge("A", "B", "AB");
    Network<String, String> network = ImmutableNetwork.copyOf(mutableNetwork);

    assertNodeNotInGraphErrorMessage(e);
  }

  @Test
  public void edgesConnecting_checkReturnedSetMutability() {
    network.addNode(N1);
    network.addNode(N2);
    Set<String> edgesConnecting = network.edgesConnecting(N1, N2);
    UnsupportedOperationException e =
        assertThrows(UnsupportedOperationException.class, () -> edgesConnecting.add(E23));

  }

  @Override
  @Test
  public void edgesConnecting_checkReturnedSetMutability() {
    addNode(N1);
    addNode(N2);
    Set<String> edgesConnecting = network.edgesConnecting(N1, N2);
    UnsupportedOperationException e =
        assertThrows(UnsupportedOperationException.class, () -> edgesConnecting.add(E23));
    addEdge(N1, N2, E12);
    assertThat(network.edgesConnecting(N1, N2)).containsExactlyElementsIn(edgesConnecting);

  }

  @Override
  public Set<N> adjacentNodes() {
    return Collections.unmodifiableSet(((BiMap<E, N>) incidentEdgeMap).values());
  }

  @Override
  public Set<E> edgesConnecting(N node) {
    return new EdgesConnecting<>(((BiMap<E, N>) incidentEdgeMap).inverse(), node);
  }

    }
  }

  @Override
  @Test
  public void edgesConnecting_checkReturnedSetMutability() {
    assume().that(graphIsMutable()).isTrue();

    addNode(N1);
    addNode(N2);
    Set<String> edgesConnecting = network.edgesConnecting(N1, N2);
    UnsupportedOperationException e =
        assertThrows(UnsupportedOperationException.class, () -> edgesConnecting.add(E23));
    addEdge(N1, N2, E12);

    }
  }

  @Override
  @Test
  public void edgesConnecting_checkReturnedSetMutability() {
    assume().that(graphIsMutable()).isTrue();

    addNode(N1);
    addNode(N2);
    Set<String> edgesConnecting = network.edgesConnecting(N1, N2);
    UnsupportedOperationException e =
        assertThrows(UnsupportedOperationException.class, () -> edgesConnecting.add(E23));
    addEdge(N1, N2, E12);

    assertThat(directedGraph.edges()).isEmpty();
    assertThat(directedGraph.addEdge(N1, N2, E12)).isTrue();
    assertThat(directedGraph.edgesConnecting(N1, N2)).isEqualTo(ImmutableSet.of(E12));
    assertThat(directedGraph.edgesConnecting(N2, N1)).isEmpty();

    // By default, parallel edges are not allowed.
    IllegalArgumentException e =

  }

  @Test
  public void edgesConnecting_parallelEdges_undirected() {
    assume().that(network.allowsParallelEdges()).isTrue();
    assume().that(network.isDirected()).isFalse();

    addEdge(N1, N2, E12);
    addEdge(N1, N2, E12_A);
    addEdge(N2, N1, E21);

    assertThat(network.edgesConnecting(N1, N2)).containsExactly(E12, E12_A, E21);

    assertNodeNotInGraphErrorMessage(e);
  }

  @Test
  public void edgesConnecting_checkReturnedSetMutability() {
    network.addNode(N1);
    network.addNode(N2);
    Set<String> edgesConnecting = network.edgesConnecting(N1, N2);
    UnsupportedOperationException e =
        assertThrows(UnsupportedOperationException.class, () -> edgesConnecting.add(E23));