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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one
3    * or more contributor license agreements.  See the NOTICE file
4    * distributed with this work for additional information
5    * regarding copyright ownership.  The ASF licenses this file
6    * to you under the Apache License, Version 2.0 (the
7    * "License"); you may not use this file except in compliance
8    * with the License.  You may obtain a copy of the License at
9    *
10   *   http://www.apache.org/licenses/LICENSE-2.0
11   *
12   * Unless required by applicable law or agreed to in writing,
13   * software distributed under the License is distributed on an
14   * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
15   * KIND, either express or implied.  See the License for the
16   * specific language governing permissions and limitations
17   * under the License.
18   */
19  package org.eclipse.aether.util.graph.visitor;
20  
21  import java.util.function.Consumer;
22  
23  import org.eclipse.aether.ConfigurationProperties;
24  import org.eclipse.aether.graph.DependencyNode;
25  
26  /**
27   * Processes dependency graph by traversing the graph in postorder. This visitor visits each node exactly once
28   * regardless how many paths within the dependency graph lead to the node such that the resulting node sequence is
29   * free of duplicates.
30   *
31   * @since 2.0.0
32   */
33  public final class PostorderDependencyNodeConsumerVisitor extends AbstractDependencyNodeConsumerVisitor {
34  
35      public static final String NAME = ConfigurationProperties.REPOSITORY_SYSTEM_DEPENDENCY_VISITOR_POSTORDER;
36  
37      private final Stack<Boolean> visits;
38  
39      /**
40       * Creates a new postorder list generator.
41       */
42      public PostorderDependencyNodeConsumerVisitor(Consumer<DependencyNode> nodeConsumer) {
43          super(nodeConsumer);
44          visits = new Stack<>();
45      }
46  
47      @Override
48      public boolean visitEnter(DependencyNode node) {
49          boolean visited = !setVisited(node);
50          visits.push(visited);
51          return !visited;
52      }
53  
54      @Override
55      public boolean visitLeave(DependencyNode node) {
56          Boolean visited = visits.pop();
57          if (visited) {
58              return true;
59          }
60          nodeConsumer.accept(node);
61          return true;
62      }
63  }