ImmutableNetwork.java

/*
 * Copyright (C) 2014 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.graph;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.Beta;
import com.google.common.base.Function;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.Maps;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import com.google.errorprone.annotations.Immutable;
import java.util.Map;

/**
 * A {@link Network} whose elements and structural relationships will never change. Instances of
 * this class may be obtained with {@link #copyOf(Network)}.
 *
 * <p>See the Guava User's Guide's <a
 * href="https://github.com/google/guava/wiki/GraphsExplained#immutable-implementations">discussion
 * of the {@code Immutable*} types</a> for more information on the properties and guarantees
 * provided by this class.
 *
 * @author James Sexton
 * @author Joshua O'Madadhain
 * @author Omar Darwish
 * @author Jens Nyman
 * @param <N> Node parameter type
 * @param <E> Edge parameter type
 * @since 20.0
 */
@Beta
@Immutable(containerOf = {"N", "E"})
@SuppressWarnings("Immutable") // Extends StandardNetwork but uses ImmutableMaps.
@ElementTypesAreNonnullByDefault
public final class ImmutableNetwork<N, E> extends StandardNetwork<N, E> {

  private ImmutableNetwork(Network<N, E> network) {
    super(
        NetworkBuilder.from(network), getNodeConnections(network), getEdgeToReferenceNode(network));
  }

  /** Returns an immutable copy of {@code network}. */
  public static <N, E> ImmutableNetwork<N, E> copyOf(Network<N, E> network) {
    return (network instanceof ImmutableNetwork)
        ? (ImmutableNetwork<N, E>) network
        : new ImmutableNetwork<N, E>(network);
  }

  /**
   * Simply returns its argument.
   *
   * @deprecated no need to use this
   */
  @Deprecated
  public static <N, E> ImmutableNetwork<N, E> copyOf(ImmutableNetwork<N, E> network) {
    return checkNotNull(network);
  }

  @Override
  public ImmutableGraph<N> asGraph() {
    return new ImmutableGraph<>(super.asGraph()); // safe because the view is effectively immutable
  }

  private static <N, E> Map<N, NetworkConnections<N, E>> getNodeConnections(Network<N, E> network) {
    // ImmutableMap.Builder maintains the order of the elements as inserted, so the map will have
    // whatever ordering the network's nodes do, so ImmutableSortedMap is unnecessary even if the
    // input nodes are sorted.
    ImmutableMap.Builder<N, NetworkConnections<N, E>> nodeConnections = ImmutableMap.builder();
    for (N node : network.nodes()) {
      nodeConnections.put(node, connectionsOf(network, node));
    }
    return nodeConnections.buildOrThrow();
  }

  private static <N, E> Map<E, N> getEdgeToReferenceNode(Network<N, E> network) {
    // ImmutableMap.Builder maintains the order of the elements as inserted, so the map will have
    // whatever ordering the network's edges do, so ImmutableSortedMap is unnecessary even if the
    // input edges are sorted.
    ImmutableMap.Builder<E, N> edgeToReferenceNode = ImmutableMap.builder();
    for (E edge : network.edges()) {
      edgeToReferenceNode.put(edge, network.incidentNodes(edge).nodeU());
    }
    return edgeToReferenceNode.buildOrThrow();
  }

  private static <N, E> NetworkConnections<N, E> connectionsOf(Network<N, E> network, N node) {
    if (network.isDirected()) {
      Map<E, N> inEdgeMap = Maps.asMap(network.inEdges(node), sourceNodeFn(network));
      Map<E, N> outEdgeMap = Maps.asMap(network.outEdges(node), targetNodeFn(network));
      int selfLoopCount = network.edgesConnecting(node, node).size();
      return network.allowsParallelEdges()
          ? DirectedMultiNetworkConnections.ofImmutable(inEdgeMap, outEdgeMap, selfLoopCount)
          : DirectedNetworkConnections.ofImmutable(inEdgeMap, outEdgeMap, selfLoopCount);
    } else {
      Map<E, N> incidentEdgeMap =
          Maps.asMap(network.incidentEdges(node), adjacentNodeFn(network, node));
      return network.allowsParallelEdges()
          ? UndirectedMultiNetworkConnections.ofImmutable(incidentEdgeMap)
          : UndirectedNetworkConnections.ofImmutable(incidentEdgeMap);
    }
  }

  private static <N, E> Function<E, N> sourceNodeFn(Network<N, E> network) {
    return (E edge) -> network.incidentNodes(edge).source();
  }

  private static <N, E> Function<E, N> targetNodeFn(Network<N, E> network) {
    return (E edge) -> network.incidentNodes(edge).target();
  }

  private static <N, E> Function<E, N> adjacentNodeFn(Network<N, E> network, N node) {
    return (E edge) -> network.incidentNodes(edge).adjacentNode(node);
  }

  /**
   * A builder for creating {@link ImmutableNetwork} instances, especially {@code static final}
   * networks. Example:
   *
   * <pre>{@code
   * static final ImmutableNetwork<City, Train> TRAIN_NETWORK =
   *     NetworkBuilder.undirected()
   *         .allowsParallelEdges(true)
   *         .<City, Train>immutable()
   *         .addEdge(PARIS, BRUSSELS, Thalys.trainNumber("1111"))
   *         .addEdge(PARIS, BRUSSELS, RegionalTrain.trainNumber("2222"))
   *         .addEdge(LONDON, PARIS, Eurostar.trainNumber("3333"))
   *         .addEdge(LONDON, BRUSSELS, Eurostar.trainNumber("4444"))
   *         .addNode(REYKJAVIK)
   *         .build();
   * }</pre>
   *
   * <p>Builder instances can be reused; it is safe to call {@link #build} multiple times to build
   * multiple networks in series. Each new network contains all the elements of the ones created
   * before it.
   *
   * @since 28.0
   */
  public static class Builder<N, E> {

    private final MutableNetwork<N, E> mutableNetwork;

    Builder(NetworkBuilder<N, E> networkBuilder) {
      this.mutableNetwork = networkBuilder.build();
    }

    /**
     * Adds {@code node} if it is not already present.
     *
     * <p><b>Nodes must be unique</b>, just as {@code Map} keys must be. They must also be non-null.
     *
     * @return this {@code Builder} object
     */
    @CanIgnoreReturnValue
    public ImmutableNetwork.Builder<N, E> addNode(N node) {
      mutableNetwork.addNode(node);
      return this;
    }

    /**
     * Adds {@code edge} connecting {@code nodeU} to {@code nodeV}.
     *
     * <p>If the network is directed, {@code edge} will be directed in this network; otherwise, it
     * will be undirected.
     *
     * <p><b>{@code edge} must be unique to this network</b>, just as a {@code Map} key must be. It
     * must also be non-null.
     *
     * <p>If {@code nodeU} and {@code nodeV} are not already present in this network, this method
     * will silently {@link #addNode(Object) add} {@code nodeU} and {@code nodeV} to the network.
     *
     * <p>If {@code edge} already connects {@code nodeU} to {@code nodeV} (in the specified order if
     * this network {@link #isDirected()}, else in any order), then this method will have no effect.
     *
     * @return this {@code Builder} object
     * @throws IllegalArgumentException if {@code edge} already exists in the network and does not
     *     connect {@code nodeU} to {@code nodeV}
     * @throws IllegalArgumentException if the introduction of the edge would violate {@link
     *     #allowsParallelEdges()} or {@link #allowsSelfLoops()}
     */
    @CanIgnoreReturnValue
    public ImmutableNetwork.Builder<N, E> addEdge(N nodeU, N nodeV, E edge) {
      mutableNetwork.addEdge(nodeU, nodeV, edge);
      return this;
    }

    /**
     * Adds {@code edge} connecting {@code endpoints}. In an undirected network, {@code edge} will
     * also connect {@code nodeV} to {@code nodeU}.
     *
     * <p>If this network is directed, {@code edge} will be directed in this network; if it is
     * undirected, {@code edge} will be undirected in this network.
     *
     * <p>If this network is directed, {@code endpoints} must be ordered.
     *
     * <p><b>{@code edge} must be unique to this network</b>, just as a {@code Map} key must be. It
     * must also be non-null.
     *
     * <p>If either or both endpoints are not already present in this network, this method will
     * silently {@link #addNode(Object) add} each missing endpoint to the network.
     *
     * <p>If {@code edge} already connects an endpoint pair equal to {@code endpoints}, then this
     * method will have no effect.
     *
     * @return this {@code Builder} object
     * @throws IllegalArgumentException if {@code edge} already exists in the network and connects
     *     some other endpoint pair that is not equal to {@code endpoints}
     * @throws IllegalArgumentException if the introduction of the edge would violate {@link
     *     #allowsParallelEdges()} or {@link #allowsSelfLoops()}
     * @throws IllegalArgumentException if the endpoints are unordered and the network is directed
     */
    @CanIgnoreReturnValue
    public ImmutableNetwork.Builder<N, E> addEdge(EndpointPair<N> endpoints, E edge) {
      mutableNetwork.addEdge(endpoints, edge);
      return this;
    }

    /**
     * Returns a newly-created {@code ImmutableNetwork} based on the contents of this {@code
     * Builder}.
     */
    public ImmutableNetwork<N, E> build() {
      return ImmutableNetwork.copyOf(mutableNetwork);
    }
  }
}