001/*
002 * Copyright (C) 2016 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package com.google.common.graph;
018
019import static com.google.common.base.Preconditions.checkNotNull;
020import static java.util.Objects.requireNonNull;
021
022import com.google.common.annotations.Beta;
023import com.google.common.base.Function;
024import com.google.common.collect.ImmutableMap;
025import com.google.common.collect.Maps;
026import com.google.errorprone.annotations.CanIgnoreReturnValue;
027import com.google.errorprone.annotations.Immutable;
028
029/**
030 * A {@link ValueGraph} whose elements and structural relationships will never change. Instances of
031 * this class may be obtained with {@link #copyOf(ValueGraph)}.
032 *
033 * <p>See the Guava User's Guide's <a
034 * href="https://github.com/google/guava/wiki/GraphsExplained#immutable-implementations">discussion
035 * of the {@code Immutable*} types</a> for more information on the properties and guarantees
036 * provided by this class.
037 *
038 * @author James Sexton
039 * @author Jens Nyman
040 * @param <N> Node parameter type
041 * @param <V> Value parameter type
042 * @since 20.0
043 */
044@Beta
045@Immutable(containerOf = {"N", "V"})
046@SuppressWarnings("Immutable") // Extends StandardValueGraph but uses ImmutableMaps.
047@ElementTypesAreNonnullByDefault
048public final class ImmutableValueGraph<N, V> extends StandardValueGraph<N, V> {
049
050  private ImmutableValueGraph(ValueGraph<N, V> graph) {
051    super(ValueGraphBuilder.from(graph), getNodeConnections(graph), graph.edges().size());
052  }
053
054  /** Returns an immutable copy of {@code graph}. */
055  public static <N, V> ImmutableValueGraph<N, V> copyOf(ValueGraph<N, V> graph) {
056    return (graph instanceof ImmutableValueGraph)
057        ? (ImmutableValueGraph<N, V>) graph
058        : new ImmutableValueGraph<N, V>(graph);
059  }
060
061  /**
062   * Simply returns its argument.
063   *
064   * @deprecated no need to use this
065   */
066  @Deprecated
067  public static <N, V> ImmutableValueGraph<N, V> copyOf(ImmutableValueGraph<N, V> graph) {
068    return checkNotNull(graph);
069  }
070
071  @Override
072  public ElementOrder<N> incidentEdgeOrder() {
073    return ElementOrder.stable();
074  }
075
076  @Override
077  public ImmutableGraph<N> asGraph() {
078    return new ImmutableGraph<N>(this); // safe because the view is effectively immutable
079  }
080
081  private static <N, V> ImmutableMap<N, GraphConnections<N, V>> getNodeConnections(
082      ValueGraph<N, V> graph) {
083    // ImmutableMap.Builder maintains the order of the elements as inserted, so the map will have
084    // whatever ordering the graph's nodes do, so ImmutableSortedMap is unnecessary even if the
085    // input nodes are sorted.
086    ImmutableMap.Builder<N, GraphConnections<N, V>> nodeConnections = ImmutableMap.builder();
087    for (N node : graph.nodes()) {
088      nodeConnections.put(node, connectionsOf(graph, node));
089    }
090    return nodeConnections.build();
091  }
092
093  private static <N, V> GraphConnections<N, V> connectionsOf(
094      final ValueGraph<N, V> graph, final N node) {
095    Function<N, V> successorNodeToValueFn =
096        new Function<N, V>() {
097          @Override
098          public V apply(N successorNode) {
099            // requireNonNull is safe because the endpoint pair comes from the graph.
100            return requireNonNull(graph.edgeValueOrDefault(node, successorNode, null));
101          }
102        };
103    return graph.isDirected()
104        ? DirectedGraphConnections.ofImmutable(
105            node, graph.incidentEdges(node), successorNodeToValueFn)
106        : UndirectedGraphConnections.ofImmutable(
107            Maps.asMap(graph.adjacentNodes(node), successorNodeToValueFn));
108  }
109
110  /**
111   * A builder for creating {@link ImmutableValueGraph} instances, especially {@code static final}
112   * graphs. Example:
113   *
114   * <pre>{@code
115   * static final ImmutableValueGraph<City, Distance> CITY_ROAD_DISTANCE_GRAPH =
116   *     ValueGraphBuilder.undirected()
117   *         .<City, Distance>immutable()
118   *         .putEdgeValue(PARIS, BERLIN, kilometers(1060))
119   *         .putEdgeValue(PARIS, BRUSSELS, kilometers(317))
120   *         .putEdgeValue(BERLIN, BRUSSELS, kilometers(764))
121   *         .addNode(REYKJAVIK)
122   *         .build();
123   * }</pre>
124   *
125   * <p>Builder instances can be reused; it is safe to call {@link #build} multiple times to build
126   * multiple graphs in series. Each new graph contains all the elements of the ones created before
127   * it.
128   *
129   * @since 28.0
130   */
131  public static class Builder<N, V> {
132
133    private final MutableValueGraph<N, V> mutableValueGraph;
134
135    Builder(ValueGraphBuilder<N, V> graphBuilder) {
136      // The incidentEdgeOrder for immutable graphs is always stable. However, we don't want to
137      // modify this builder, so we make a copy instead.
138      this.mutableValueGraph =
139          graphBuilder.copy().incidentEdgeOrder(ElementOrder.<N>stable()).build();
140    }
141
142    /**
143     * Adds {@code node} if it is not already present.
144     *
145     * <p><b>Nodes must be unique</b>, just as {@code Map} keys must be. They must also be non-null.
146     *
147     * @return this {@code Builder} object
148     */
149    @CanIgnoreReturnValue
150    public ImmutableValueGraph.Builder<N, V> addNode(N node) {
151      mutableValueGraph.addNode(node);
152      return this;
153    }
154
155    /**
156     * Adds an edge connecting {@code nodeU} to {@code nodeV} if one is not already present, and
157     * sets a value for that edge to {@code value} (overwriting the existing value, if any).
158     *
159     * <p>If the graph is directed, the resultant edge will be directed; otherwise, it will be
160     * undirected.
161     *
162     * <p>Values do not have to be unique. However, values must be non-null.
163     *
164     * <p>If {@code nodeU} and {@code nodeV} are not already present in this graph, this method will
165     * silently {@link #addNode(Object) add} {@code nodeU} and {@code nodeV} to the graph.
166     *
167     * @return this {@code Builder} object
168     * @throws IllegalArgumentException if the introduction of the edge would violate {@link
169     *     #allowsSelfLoops()}
170     */
171    @CanIgnoreReturnValue
172    public ImmutableValueGraph.Builder<N, V> putEdgeValue(N nodeU, N nodeV, V value) {
173      mutableValueGraph.putEdgeValue(nodeU, nodeV, value);
174      return this;
175    }
176
177    /**
178     * Adds an edge connecting {@code endpoints} if one is not already present, and sets a value for
179     * that edge to {@code value} (overwriting the existing value, if any).
180     *
181     * <p>If the graph is directed, the resultant edge will be directed; otherwise, it will be
182     * undirected.
183     *
184     * <p>If this graph is directed, {@code endpoints} must be ordered.
185     *
186     * <p>Values do not have to be unique. However, values must be non-null.
187     *
188     * <p>If either or both endpoints are not already present in this graph, this method will
189     * silently {@link #addNode(Object) add} each missing endpoint to the graph.
190     *
191     * @return this {@code Builder} object
192     * @throws IllegalArgumentException if the introduction of the edge would violate {@link
193     *     #allowsSelfLoops()}
194     * @throws IllegalArgumentException if the endpoints are unordered and the graph is directed
195     */
196    @CanIgnoreReturnValue
197    public ImmutableValueGraph.Builder<N, V> putEdgeValue(EndpointPair<N> endpoints, V value) {
198      mutableValueGraph.putEdgeValue(endpoints, value);
199      return this;
200    }
201
202    /**
203     * Returns a newly-created {@code ImmutableValueGraph} based on the contents of this {@code
204     * Builder}.
205     */
206    public ImmutableValueGraph<N, V> build() {
207      return ImmutableValueGraph.copyOf(mutableValueGraph);
208    }
209  }
210}