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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.ArrayList;
22  import java.util.HashMap;
23  import java.util.function.Consumer;
24  
25  import org.eclipse.aether.graph.DependencyNode;
26  
27  /**
28   * Processes dependency graph by traversing the graph in level order. This visitor visits each node exactly once
29   * regardless how many paths within the dependency graph lead to the node such that the resulting node sequence is
30   * free of duplicates.
31   *
32   * @since TBD
33   */
34  public final class LevelOrderDependencyNodeConsumerVisitor extends AbstractDependencyNodeConsumerVisitor {
35  
36      public static final String NAME = "levelOrder";
37  
38      private final HashMap<Integer, ArrayList<DependencyNode>> nodesPerLevel;
39  
40      private final Stack<Boolean> visits;
41  
42      /**
43       * Creates a new level order list generator.
44       */
45      public LevelOrderDependencyNodeConsumerVisitor(Consumer<DependencyNode> nodeConsumer) {
46          super(nodeConsumer);
47          nodesPerLevel = new HashMap<>(16);
48          visits = new Stack<>();
49      }
50  
51      @Override
52      public boolean visitEnter(DependencyNode node) {
53          boolean visited = !setVisited(node);
54          visits.push(visited);
55          if (!visited) {
56              nodesPerLevel.computeIfAbsent(visits.size(), k -> new ArrayList<>()).add(node);
57          }
58          return !visited;
59      }
60  
61      @Override
62      public boolean visitLeave(DependencyNode node) {
63          Boolean visited = visits.pop();
64          if (visited) {
65              return true;
66          }
67          if (visits.isEmpty()) {
68              for (int l = 1; nodesPerLevel.containsKey(l); l++) {
69                  nodesPerLevel.get(l).forEach(nodeConsumer);
70              }
71          }
72          return true;
73      }
74  }