001/*
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *   http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing,
013 * software distributed under the License is distributed on an
014 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015 * KIND, either express or implied.  See the License for the
016 * specific language governing permissions and limitations
017 * under the License.
018 */
019package org.eclipse.aether.util.graph.visitor;
020
021import java.util.function.Consumer;
022
023import org.eclipse.aether.ConfigurationProperties;
024import org.eclipse.aether.graph.DependencyNode;
025
026/**
027 * Processes dependency graph by traversing the graph in postorder. This visitor visits each node exactly once
028 * regardless how many paths within the dependency graph lead to the node such that the resulting node sequence is
029 * free of duplicates.
030 *
031 * @since 2.0.0
032 *
033 * @see NodeListGenerator
034 */
035public final class PostorderDependencyNodeConsumerVisitor extends AbstractDependencyNodeConsumerVisitor {
036
037    public static final String NAME = ConfigurationProperties.REPOSITORY_SYSTEM_DEPENDENCY_VISITOR_POSTORDER;
038
039    private final Stack<Boolean> visits;
040
041    /**
042     * Creates a new postorder list generator.
043     */
044    public PostorderDependencyNodeConsumerVisitor(Consumer<DependencyNode> nodeConsumer) {
045        super(nodeConsumer);
046        visits = new Stack<>();
047    }
048
049    @Override
050    public boolean visitEnter(DependencyNode node) {
051        boolean visited = !setVisited(node);
052        visits.push(visited);
053        return !visited;
054    }
055
056    @Override
057    public boolean visitLeave(DependencyNode node) {
058        Boolean visited = visits.pop();
059        if (visited) {
060            return true;
061        }
062        nodeConsumer.accept(node);
063        return true;
064    }
065}