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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.List;
24  import java.util.function.Consumer;
25  
26  import org.eclipse.aether.ConfigurationProperties;
27  import org.eclipse.aether.graph.DependencyFilter;
28  import org.eclipse.aether.graph.DependencyNode;
29  
30  /**
31   * Processes dependency graph by traversing the graph in level order. This visitor visits each node exactly once
32   * regardless how many paths within the dependency graph lead to the node such that the resulting node sequence is
33   * free of duplicates.
34   * <p>
35   * <strong>Instances of this class cannot be embedded into {@link FilteringDependencyVisitor}</strong>, pass in the
36   * filter {@link DependencyFilter} into  constructor instead.
37   *
38   * @see NodeListGenerator
39   * @since 2.0.0
40   */
41  public final class LevelOrderDependencyNodeConsumerVisitor extends AbstractDependencyNodeConsumerVisitor {
42  
43      public static final String NAME = ConfigurationProperties.REPOSITORY_SYSTEM_DEPENDENCY_VISITOR_LEVELORDER;
44  
45      private final HashMap<Integer, ArrayList<DependencyNode>> nodesPerLevel;
46  
47      private final Stack<Boolean> visits;
48  
49      /**
50       * Creates a new level order list generator.
51       */
52      public LevelOrderDependencyNodeConsumerVisitor(Consumer<DependencyNode> nodeConsumer) {
53          this(nodeConsumer, null);
54      }
55  
56      /**
57       * Creates a new level order list generator with filter.
58       *
59       * @since 2.0.12
60       */
61      public LevelOrderDependencyNodeConsumerVisitor(Consumer<DependencyNode> nodeConsumer, DependencyFilter filter) {
62          super(nodeConsumer, filter);
63          nodesPerLevel = new HashMap<>(16);
64          visits = new Stack<>();
65      }
66  
67      @Override
68      protected boolean doVisitEnter(DependencyNode node) {
69          boolean visited = !setVisited(node);
70          visits.push(visited);
71          if (!visited) {
72              List<DependencyNode> nodesOnLevel = nodesPerLevel.computeIfAbsent(visits.size(), k -> new ArrayList<>());
73              if (acceptNode(node)) {
74                  nodesOnLevel.add(node);
75              }
76          }
77          return !visited;
78      }
79  
80      @Override
81      protected boolean doVisitLeave(DependencyNode node) {
82          Boolean visited = visits.pop();
83          if (visited) {
84              return true;
85          }
86          if (visits.isEmpty()) {
87              for (int l = 1; nodesPerLevel.containsKey(l); l++) {
88                  nodesPerLevel.get(l).forEach(this::consumeNode);
89              }
90          }
91          return true;
92      }
93  }