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/*
 * Copyright (C) 2016 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.graph;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.Beta;
import com.google.common.base.Function;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.Maps;
import com.google.errorprone.annotations.Immutable;

/**
 * A {@link ValueGraph} whose elements and structural relationships will never change. Instances of
 * this class may be obtained with {@link #copyOf(ValueGraph)}.
 *
 * See the Guava User's Guide's discussion
 * of the {@code Immutable*} types for more information on the properties and guarantees
 * provided by this class.
 *
 * @author James Sexton
 * @param  Node parameter type
 * @param  Value parameter type
 * @since 20.0
 */
@Beta
@Immutable(containerOf = {"N", "V"})
@SuppressWarnings("Immutable") // Extends ConfigurableValueGraph but uses ImmutableMaps.
public final class ImmutableValueGraph extends ConfigurableValueGraph {

  private ImmutableValueGraph(ValueGraph graph) {
    super(ValueGraphBuilder.from(graph), getNodeConnections(graph), graph.edges().size());
  }

  /** Returns an immutable copy of {@code graph}. */
  public static  ImmutableValueGraph copyOf(ValueGraph graph) {
    return (graph instanceof ImmutableValueGraph)
        ? (ImmutableValueGraph) graph
        : new ImmutableValueGraph(graph);
  }

  /**
   * Simply returns its argument.
   *
   * @deprecated no need to use this
   */
  @Deprecated
  public static  ImmutableValueGraph copyOf(ImmutableValueGraph graph) {
    return checkNotNull(graph);
  }

  @Override
  public ImmutableGraph asGraph() {
    return new ImmutableGraph(this); // safe because the view is effectively immutable
  }

  private static  ImmutableMap> getNodeConnections(
      ValueGraph graph) {
    // ImmutableMap.Builder maintains the order of the elements as inserted, so the map will have
    // whatever ordering the graph's nodes do, so ImmutableSortedMap is unnecessary even if the
    // input nodes are sorted.
    ImmutableMap.Builder> nodeConnections = ImmutableMap.builder();
    for (N node : graph.nodes()) {
      nodeConnections.put(node, connectionsOf(graph, node));
    }
    return nodeConnections.build();
  }

  private static  GraphConnections connectionsOf(
      final ValueGraph graph, final N node) {
    Function successorNodeToValueFn =
        new Function() {
          @Override
          public V apply(N successorNode) {
            return graph.edgeValueOrDefault(node, successorNode, null);
          }
        };
    return graph.isDirected()
        ? DirectedGraphConnections.ofImmutable(
            graph.predecessors(node), Maps.asMap(graph.successors(node), successorNodeToValueFn))
        : UndirectedGraphConnections.ofImmutable(
            Maps.asMap(graph.adjacentNodes(node), successorNodeToValueFn));
  }
}