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<>(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.buildOrThrow();
091  }
092
093  private static <N, V> GraphConnections<N, V> connectionsOf(ValueGraph<N, V> graph, N node) {
094    Function<N, V> successorNodeToValueFn =
095        (N successorNode) ->
096            // requireNonNull is safe because the endpoint pair comes from the graph.
097            requireNonNull(graph.edgeValueOrDefault(node, successorNode, null));
098    return graph.isDirected()
099        ? DirectedGraphConnections.ofImmutable(
100            node, graph.incidentEdges(node), successorNodeToValueFn)
101        : UndirectedGraphConnections.ofImmutable(
102            Maps.asMap(graph.adjacentNodes(node), successorNodeToValueFn));
103  }
104
105  /**
106   * A builder for creating {@link ImmutableValueGraph} instances, especially {@code static final}
107   * graphs. Example:
108   *
109   * <pre>{@code
110   * static final ImmutableValueGraph<City, Distance> CITY_ROAD_DISTANCE_GRAPH =
111   *     ValueGraphBuilder.undirected()
112   *         .<City, Distance>immutable()
113   *         .putEdgeValue(PARIS, BERLIN, kilometers(1060))
114   *         .putEdgeValue(PARIS, BRUSSELS, kilometers(317))
115   *         .putEdgeValue(BERLIN, BRUSSELS, kilometers(764))
116   *         .addNode(REYKJAVIK)
117   *         .build();
118   * }</pre>
119   *
120   * <p>Builder instances can be reused; it is safe to call {@link #build} multiple times to build
121   * multiple graphs in series. Each new graph contains all the elements of the ones created before
122   * it.
123   *
124   * @since 28.0
125   */
126  public static class Builder<N, V> {
127
128    private final MutableValueGraph<N, V> mutableValueGraph;
129
130    Builder(ValueGraphBuilder<N, V> graphBuilder) {
131      // The incidentEdgeOrder for immutable graphs is always stable. However, we don't want to
132      // modify this builder, so we make a copy instead.
133      this.mutableValueGraph =
134          graphBuilder.copy().incidentEdgeOrder(ElementOrder.<N>stable()).build();
135    }
136
137    /**
138     * Adds {@code node} if it is not already present.
139     *
140     * <p><b>Nodes must be unique</b>, just as {@code Map} keys must be. They must also be non-null.
141     *
142     * @return this {@code Builder} object
143     */
144    @CanIgnoreReturnValue
145    public ImmutableValueGraph.Builder<N, V> addNode(N node) {
146      mutableValueGraph.addNode(node);
147      return this;
148    }
149
150    /**
151     * Adds an edge connecting {@code nodeU} to {@code nodeV} if one is not already present, and
152     * sets a value for that edge to {@code value} (overwriting the existing value, if any).
153     *
154     * <p>If the graph is directed, the resultant edge will be directed; otherwise, it will be
155     * undirected.
156     *
157     * <p>Values do not have to be unique. However, values must be non-null.
158     *
159     * <p>If {@code nodeU} and {@code nodeV} are not already present in this graph, this method will
160     * silently {@link #addNode(Object) add} {@code nodeU} and {@code nodeV} to the graph.
161     *
162     * @return this {@code Builder} object
163     * @throws IllegalArgumentException if the introduction of the edge would violate {@link
164     *     #allowsSelfLoops()}
165     */
166    @CanIgnoreReturnValue
167    public ImmutableValueGraph.Builder<N, V> putEdgeValue(N nodeU, N nodeV, V value) {
168      mutableValueGraph.putEdgeValue(nodeU, nodeV, value);
169      return this;
170    }
171
172    /**
173     * Adds an edge connecting {@code endpoints} if one is not already present, and sets a value for
174     * that edge to {@code value} (overwriting the existing value, if any).
175     *
176     * <p>If the graph is directed, the resultant edge will be directed; otherwise, it will be
177     * undirected.
178     *
179     * <p>If this graph is directed, {@code endpoints} must be ordered.
180     *
181     * <p>Values do not have to be unique. However, values must be non-null.
182     *
183     * <p>If either or both endpoints are not already present in this graph, this method will
184     * silently {@link #addNode(Object) add} each missing endpoint to the graph.
185     *
186     * @return this {@code Builder} object
187     * @throws IllegalArgumentException if the introduction of the edge would violate {@link
188     *     #allowsSelfLoops()}
189     * @throws IllegalArgumentException if the endpoints are unordered and the graph is directed
190     */
191    @CanIgnoreReturnValue
192    public ImmutableValueGraph.Builder<N, V> putEdgeValue(EndpointPair<N> endpoints, V value) {
193      mutableValueGraph.putEdgeValue(endpoints, value);
194      return this;
195    }
196
197    /**
198     * Returns a newly-created {@code ImmutableValueGraph} based on the contents of this {@code
199     * Builder}.
200     */
201    public ImmutableValueGraph<N, V> build() {
202      return ImmutableValueGraph.copyOf(mutableValueGraph);
203    }
204  }
205}