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 ConfigurableValueGraph but uses ImmutableMaps.
046public final class ImmutableValueGraph<N, V> extends ConfigurableValueGraph<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 ImmutableGraph<N> asGraph() {
071    return new ImmutableGraph<N>(this); // safe because the view is effectively immutable
072  }
073
074  private static <N, V> ImmutableMap<N, GraphConnections<N, V>> getNodeConnections(
075      ValueGraph<N, V> graph) {
076    // ImmutableMap.Builder maintains the order of the elements as inserted, so the map will have
077    // whatever ordering the graph's nodes do, so ImmutableSortedMap is unnecessary even if the
078    // input nodes are sorted.
079    ImmutableMap.Builder<N, GraphConnections<N, V>> nodeConnections = ImmutableMap.builder();
080    for (N node : graph.nodes()) {
081      nodeConnections.put(node, connectionsOf(graph, node));
082    }
083    return nodeConnections.build();
084  }
085
086  private static <N, V> GraphConnections<N, V> connectionsOf(
087      final ValueGraph<N, V> graph, final N node) {
088    Function<N, V> successorNodeToValueFn =
089        new Function<N, V>() {
090          @Override
091          public V apply(N successorNode) {
092            return graph.edgeValueOrDefault(node, successorNode, null);
093          }
094        };
095    return graph.isDirected()
096        ? DirectedGraphConnections.ofImmutable(
097            graph.predecessors(node), Maps.asMap(graph.successors(node), successorNodeToValueFn))
098        : UndirectedGraphConnections.ofImmutable(
099            Maps.asMap(graph.adjacentNodes(node), successorNodeToValueFn));
100  }
101
102  /**
103   * A builder for creating {@link ImmutableValueGraph} instances, especially {@code static final}
104   * graphs. Example:
105   *
106   * <pre>{@code
107   * static final ImmutableValueGraph<City, Distance> CITY_ROAD_DISTANCE_GRAPH =
108   *     ValueGraphBuilder.undirected()
109   *         .<City, Distance>immutable()
110   *         .putEdgeValue(PARIS, BERLIN, kilometers(1060))
111   *         .putEdgeValue(PARIS, BRUSSELS, kilometers(317))
112   *         .putEdgeValue(BERLIN, BRUSSELS, kilometers(764))
113   *         .addNode(REYKJAVIK)
114   *         .build();
115   * }</pre>
116   *
117   * <p>Builder instances can be reused; it is safe to call {@link #build} multiple times to build
118   * multiple graphs in series. Each new graph contains all the elements of the ones created before
119   * it.
120   *
121   * @since 28.0
122   */
123  public static class Builder<N, V> {
124
125    private final MutableValueGraph<N, V> mutableValueGraph;
126
127    Builder(ValueGraphBuilder<N, V> graphBuilder) {
128      this.mutableValueGraph = graphBuilder.build();
129    }
130
131    /**
132     * Adds {@code node} if it is not already present.
133     *
134     * <p><b>Nodes must be unique</b>, just as {@code Map} keys must be. They must also be non-null.
135     *
136     * @return this {@code Builder} object
137     */
138    @CanIgnoreReturnValue
139    public ImmutableValueGraph.Builder<N, V> addNode(N node) {
140      mutableValueGraph.addNode(node);
141      return this;
142    }
143
144    /**
145     * Adds an edge connecting {@code nodeU} to {@code nodeV} if one is not already present, and
146     * sets a value for that edge to {@code value} (overwriting the existing value, if any).
147     *
148     * <p>If the graph is directed, the resultant edge will be directed; otherwise, it will be
149     * undirected.
150     *
151     * <p>Values do not have to be unique. However, values must be non-null.
152     *
153     * <p>If {@code nodeU} and {@code nodeV} are not already present in this graph, this method will
154     * silently {@link #addNode(Object) add} {@code nodeU} and {@code nodeV} to the graph.
155     *
156     * @return this {@code Builder} object
157     * @throws IllegalArgumentException if the introduction of the edge would violate {@link
158     *     #allowsSelfLoops()}
159     */
160    @CanIgnoreReturnValue
161    public ImmutableValueGraph.Builder<N, V> putEdgeValue(N nodeU, N nodeV, V value) {
162      mutableValueGraph.putEdgeValue(nodeU, nodeV, value);
163      return this;
164    }
165
166    /**
167     * Adds an edge connecting {@code endpoints} if one is not already present, and sets a value for
168     * that edge to {@code value} (overwriting the existing value, if any).
169     *
170     * <p>If the graph is directed, the resultant edge will be directed; otherwise, it will be
171     * undirected.
172     *
173     * <p>If this graph is directed, {@code endpoints} must be ordered.
174     *
175     * <p>Values do not have to be unique. However, values must be non-null.
176     *
177     * <p>If either or both endpoints are not already present in this graph, this method will
178     * silently {@link #addNode(Object) add} each missing endpoint to the graph.
179     *
180     * @return this {@code Builder} object
181     * @throws IllegalArgumentException if the introduction of the edge would violate {@link
182     *     #allowsSelfLoops()}
183     * @throws IllegalArgumentException if the endpoints are unordered and the graph is directed
184     */
185    @CanIgnoreReturnValue
186    public ImmutableValueGraph.Builder<N, V> putEdgeValue(EndpointPair<N> endpoints, V value) {
187      mutableValueGraph.putEdgeValue(endpoints, value);
188      return this;
189    }
190
191    /**
192     * Returns a newly-created {@code ImmutableValueGraph} based on the contents of this {@code
193     * Builder}.
194     */
195    public ImmutableValueGraph<N, V> build() {
196      return ImmutableValueGraph.copyOf(mutableValueGraph);
197    }
198  }
199}