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;
020
021import com.google.common.annotations.Beta;
022import com.google.common.base.Function;
023import com.google.common.collect.ImmutableMap;
024import com.google.common.collect.Maps;
025import com.google.errorprone.annotations.CanIgnoreReturnValue;
026import com.google.errorprone.annotations.Immutable;
027
028/**
029 * A {@link ValueGraph} whose elements and structural relationships will never change. Instances of
030 * this class may be obtained with {@link #copyOf(ValueGraph)}.
031 *
032 * <p>See the Guava User's Guide's <a
033 * href="https://github.com/google/guava/wiki/GraphsExplained#immutable-implementations">discussion
034 * of the {@code Immutable*} types</a> for more information on the properties and guarantees
035 * provided by this class.
036 *
037 * @author James Sexton
038 * @author Jens Nyman
039 * @param <N> Node parameter type
040 * @param <V> Value parameter type
041 * @since 20.0
042 */
043@Beta
044@Immutable(containerOf = {"N", "V"})
045@SuppressWarnings("Immutable") // Extends StandardValueGraph but uses ImmutableMaps.
046public final class ImmutableValueGraph<N, V> extends StandardValueGraph<N, V> {
047
048  private ImmutableValueGraph(ValueGraph<N, V> graph) {
049    super(ValueGraphBuilder.from(graph), getNodeConnections(graph), graph.edges().size());
050  }
051
052  /** Returns an immutable copy of {@code graph}. */
053  public static <N, V> ImmutableValueGraph<N, V> copyOf(ValueGraph<N, V> graph) {
054    return (graph instanceof ImmutableValueGraph)
055        ? (ImmutableValueGraph<N, V>) graph
056        : new ImmutableValueGraph<N, V>(graph);
057  }
058
059  /**
060   * Simply returns its argument.
061   *
062   * @deprecated no need to use this
063   */
064  @Deprecated
065  public static <N, V> ImmutableValueGraph<N, V> copyOf(ImmutableValueGraph<N, V> graph) {
066    return checkNotNull(graph);
067  }
068
069  @Override
070  public ElementOrder<N> incidentEdgeOrder() {
071    return ElementOrder.stable();
072  }
073
074  @Override
075  public ImmutableGraph<N> asGraph() {
076    return new ImmutableGraph<N>(this); // safe because the view is effectively immutable
077  }
078
079  private static <N, V> ImmutableMap<N, GraphConnections<N, V>> getNodeConnections(
080      ValueGraph<N, V> graph) {
081    // ImmutableMap.Builder maintains the order of the elements as inserted, so the map will have
082    // whatever ordering the graph's nodes do, so ImmutableSortedMap is unnecessary even if the
083    // input nodes are sorted.
084    ImmutableMap.Builder<N, GraphConnections<N, V>> nodeConnections = ImmutableMap.builder();
085    for (N node : graph.nodes()) {
086      nodeConnections.put(node, connectionsOf(graph, node));
087    }
088    return nodeConnections.build();
089  }
090
091  private static <N, V> GraphConnections<N, V> connectionsOf(
092      final ValueGraph<N, V> graph, final N node) {
093    Function<N, V> successorNodeToValueFn =
094        new Function<N, V>() {
095          @Override
096          public V apply(N successorNode) {
097            return graph.edgeValueOrDefault(node, successorNode, null);
098          }
099        };
100    return graph.isDirected()
101        ? DirectedGraphConnections.ofImmutable(
102            node, graph.incidentEdges(node), successorNodeToValueFn)
103        : UndirectedGraphConnections.ofImmutable(
104            Maps.asMap(graph.adjacentNodes(node), successorNodeToValueFn));
105  }
106
107  /**
108   * A builder for creating {@link ImmutableValueGraph} instances, especially {@code static final}
109   * graphs. Example:
110   *
111   * <pre>{@code
112   * static final ImmutableValueGraph<City, Distance> CITY_ROAD_DISTANCE_GRAPH =
113   *     ValueGraphBuilder.undirected()
114   *         .<City, Distance>immutable()
115   *         .putEdgeValue(PARIS, BERLIN, kilometers(1060))
116   *         .putEdgeValue(PARIS, BRUSSELS, kilometers(317))
117   *         .putEdgeValue(BERLIN, BRUSSELS, kilometers(764))
118   *         .addNode(REYKJAVIK)
119   *         .build();
120   * }</pre>
121   *
122   * <p>Builder instances can be reused; it is safe to call {@link #build} multiple times to build
123   * multiple graphs in series. Each new graph contains all the elements of the ones created before
124   * it.
125   *
126   * @since 28.0
127   */
128  public static class Builder<N, V> {
129
130    private final MutableValueGraph<N, V> mutableValueGraph;
131
132    Builder(ValueGraphBuilder<N, V> graphBuilder) {
133      // The incidentEdgeOrder for immutable graphs is always stable. However, we don't want to
134      // modify this builder, so we make a copy instead.
135      this.mutableValueGraph =
136          graphBuilder.copy().incidentEdgeOrder(ElementOrder.<N>stable()).build();
137    }
138
139    /**
140     * Adds {@code node} if it is not already present.
141     *
142     * <p><b>Nodes must be unique</b>, just as {@code Map} keys must be. They must also be non-null.
143     *
144     * @return this {@code Builder} object
145     */
146    @CanIgnoreReturnValue
147    public ImmutableValueGraph.Builder<N, V> addNode(N node) {
148      mutableValueGraph.addNode(node);
149      return this;
150    }
151
152    /**
153     * Adds an edge connecting {@code nodeU} to {@code nodeV} if one is not already present, and
154     * sets a value for that edge to {@code value} (overwriting the existing value, if any).
155     *
156     * <p>If the graph is directed, the resultant edge will be directed; otherwise, it will be
157     * undirected.
158     *
159     * <p>Values do not have to be unique. However, values must be non-null.
160     *
161     * <p>If {@code nodeU} and {@code nodeV} are not already present in this graph, this method will
162     * silently {@link #addNode(Object) add} {@code nodeU} and {@code nodeV} to the graph.
163     *
164     * @return this {@code Builder} object
165     * @throws IllegalArgumentException if the introduction of the edge would violate {@link
166     *     #allowsSelfLoops()}
167     */
168    @CanIgnoreReturnValue
169    public ImmutableValueGraph.Builder<N, V> putEdgeValue(N nodeU, N nodeV, V value) {
170      mutableValueGraph.putEdgeValue(nodeU, nodeV, value);
171      return this;
172    }
173
174    /**
175     * Adds an edge connecting {@code endpoints} if one is not already present, and sets a value for
176     * that edge to {@code value} (overwriting the existing value, if any).
177     *
178     * <p>If the graph is directed, the resultant edge will be directed; otherwise, it will be
179     * undirected.
180     *
181     * <p>If this graph is directed, {@code endpoints} must be ordered.
182     *
183     * <p>Values do not have to be unique. However, values must be non-null.
184     *
185     * <p>If either or both endpoints are not already present in this graph, this method will
186     * silently {@link #addNode(Object) add} each missing endpoint to the graph.
187     *
188     * @return this {@code Builder} object
189     * @throws IllegalArgumentException if the introduction of the edge would violate {@link
190     *     #allowsSelfLoops()}
191     * @throws IllegalArgumentException if the endpoints are unordered and the graph is directed
192     */
193    @CanIgnoreReturnValue
194    public ImmutableValueGraph.Builder<N, V> putEdgeValue(EndpointPair<N> endpoints, V value) {
195      mutableValueGraph.putEdgeValue(endpoints, value);
196      return this;
197    }
198
199    /**
200     * Returns a newly-created {@code ImmutableValueGraph} based on the contents of this {@code
201     * Builder}.
202     */
203    public ImmutableValueGraph<N, V> build() {
204      return ImmutableValueGraph.copyOf(mutableValueGraph);
205    }
206  }
207}