001/*
002 * Copyright (C) 2014 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.base.Functions;
024import com.google.common.collect.ImmutableMap;
025import com.google.common.collect.Maps;
026import com.google.common.graph.GraphConstants.Presence;
027import com.google.errorprone.annotations.CanIgnoreReturnValue;
028import com.google.errorprone.annotations.Immutable;
029
030/**
031 * A {@link Graph} whose elements and structural relationships will never change. Instances of this
032 * class may be obtained with {@link #copyOf(Graph)}.
033 *
034 * <p>See the Guava User's Guide's <a
035 * href="https://github.com/google/guava/wiki/GraphsExplained#immutable-implementations">discussion
036 * of the {@code Immutable*} types</a> for more information on the properties and guarantees
037 * provided by this class.
038 *
039 * @author James Sexton
040 * @author Joshua O'Madadhain
041 * @author Omar Darwish
042 * @author Jens Nyman
043 * @param <N> Node parameter type
044 * @since 20.0
045 */
046@Beta
047@Immutable(containerOf = {"N"})
048public class ImmutableGraph<N> extends ForwardingGraph<N> {
049  @SuppressWarnings("Immutable") // The backing graph must be immutable.
050  private final BaseGraph<N> backingGraph;
051
052  ImmutableGraph(BaseGraph<N> backingGraph) {
053    this.backingGraph = backingGraph;
054  }
055
056  /** Returns an immutable copy of {@code graph}. */
057  public static <N> ImmutableGraph<N> copyOf(Graph<N> graph) {
058    return (graph instanceof ImmutableGraph)
059        ? (ImmutableGraph<N>) graph
060        : new ImmutableGraph<N>(
061            new ConfigurableValueGraph<N, Presence>(
062                GraphBuilder.from(graph), getNodeConnections(graph), graph.edges().size()));
063  }
064
065  /**
066   * Simply returns its argument.
067   *
068   * @deprecated no need to use this
069   */
070  @Deprecated
071  public static <N> ImmutableGraph<N> copyOf(ImmutableGraph<N> graph) {
072    return checkNotNull(graph);
073  }
074
075  private static <N> ImmutableMap<N, GraphConnections<N, Presence>> getNodeConnections(
076      Graph<N> graph) {
077    // ImmutableMap.Builder maintains the order of the elements as inserted, so the map will have
078    // whatever ordering the graph's nodes do, so ImmutableSortedMap is unnecessary even if the
079    // input nodes are sorted.
080    ImmutableMap.Builder<N, GraphConnections<N, Presence>> nodeConnections = ImmutableMap.builder();
081    for (N node : graph.nodes()) {
082      nodeConnections.put(node, connectionsOf(graph, node));
083    }
084    return nodeConnections.build();
085  }
086
087  @SuppressWarnings("unchecked")
088  private static <N> GraphConnections<N, Presence> connectionsOf(Graph<N> graph, N node) {
089    Function<N, Presence> edgeValueFn =
090        (Function<N, Presence>) Functions.constant(Presence.EDGE_EXISTS);
091    return graph.isDirected()
092        ? DirectedGraphConnections.ofImmutable(node, graph.incidentEdges(node), edgeValueFn)
093        : UndirectedGraphConnections.ofImmutable(
094            Maps.asMap(graph.adjacentNodes(node), edgeValueFn));
095  }
096
097  @Override
098  protected BaseGraph<N> delegate() {
099    return backingGraph;
100  }
101
102  /**
103   * A builder for creating {@link ImmutableGraph} instances, especially {@code static final}
104   * graphs. Example:
105   *
106   * <pre>{@code
107   * static final ImmutableGraph<Country> COUNTRY_ADJACENCY_GRAPH =
108   *     GraphBuilder.undirected()
109   *         .<Country>immutable()
110   *         .putEdge(FRANCE, GERMANY)
111   *         .putEdge(FRANCE, BELGIUM)
112   *         .putEdge(GERMANY, BELGIUM)
113   *         .addNode(ICELAND)
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> {
124
125    private final MutableGraph<N> mutableGraph;
126
127    Builder(GraphBuilder<N> graphBuilder) {
128      // The incidentEdgeOrder for immutable graphs is always stable. However, we don't want to
129      // modify this builder, so we make a copy instead.
130      this.mutableGraph = graphBuilder.copy().incidentEdgeOrder(ElementOrder.<N>stable()).build();
131    }
132
133    /**
134     * Adds {@code node} if it is not already present.
135     *
136     * <p><b>Nodes must be unique</b>, just as {@code Map} keys must be. They must also be non-null.
137     *
138     * @return this {@code Builder} object
139     */
140    @CanIgnoreReturnValue
141    public Builder<N> addNode(N node) {
142      mutableGraph.addNode(node);
143      return this;
144    }
145
146    /**
147     * Adds an edge connecting {@code nodeU} to {@code nodeV} if one is not already present.
148     *
149     * <p>If the graph is directed, the resultant edge will be directed; otherwise, it will be
150     * undirected.
151     *
152     * <p>If {@code nodeU} and {@code nodeV} are not already present in this graph, this method will
153     * silently {@link #addNode(Object) add} {@code nodeU} and {@code nodeV} to the graph.
154     *
155     * @return this {@code Builder} object
156     * @throws IllegalArgumentException if the introduction of the edge would violate {@link
157     *     #allowsSelfLoops()}
158     */
159    @CanIgnoreReturnValue
160    public Builder<N> putEdge(N nodeU, N nodeV) {
161      mutableGraph.putEdge(nodeU, nodeV);
162      return this;
163    }
164
165    /**
166     * Adds an edge connecting {@code endpoints} (in the order, if any, specified by {@code
167     * endpoints}) if one is not already present.
168     *
169     * <p>If this graph is directed, {@code endpoints} must be ordered and the added edge will be
170     * directed; if it is undirected, the added edge will be undirected.
171     *
172     * <p>If this graph is directed, {@code endpoints} must be ordered.
173     *
174     * <p>If either or both endpoints are not already present in this graph, this method will
175     * silently {@link #addNode(Object) add} each missing endpoint to the graph.
176     *
177     * @return this {@code Builder} object
178     * @throws IllegalArgumentException if the introduction of the edge would violate {@link
179     *     #allowsSelfLoops()}
180     * @throws IllegalArgumentException if the endpoints are unordered and the graph is directed
181     */
182    @CanIgnoreReturnValue
183    public Builder<N> putEdge(EndpointPair<N> endpoints) {
184      mutableGraph.putEdge(endpoints);
185      return this;
186    }
187
188    /**
189     * Returns a newly-created {@code ImmutableGraph} based on the contents of this {@code Builder}.
190     */
191    public ImmutableGraph<N> build() {
192      return ImmutableGraph.copyOf(mutableGraph);
193    }
194  }
195}