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.DependencyFilter;
025import org.eclipse.aether.graph.DependencyNode;
026
027/**
028 * Processes dependency graph by traversing the graph in postorder. This visitor visits each node exactly once
029 * regardless how many paths within the dependency graph lead to the node such that the resulting node sequence is
030 * free of duplicates.
031 * <p>
032 * <strong>Instances of this class cannot be embedded into {@link FilteringDependencyVisitor}</strong>, pass in the
033 * filter {@link DependencyFilter} into  constructor instead.
034 *
035 * @see NodeListGenerator
036 * @since 2.0.0
037 */
038public final class PostorderDependencyNodeConsumerVisitor extends AbstractDependencyNodeConsumerVisitor {
039
040    public static final String NAME = ConfigurationProperties.REPOSITORY_SYSTEM_DEPENDENCY_VISITOR_POSTORDER;
041
042    private final Stack<Boolean> visits;
043
044    /**
045     * Creates a new postorder list generator.
046     */
047    public PostorderDependencyNodeConsumerVisitor(Consumer<DependencyNode> nodeConsumer) {
048        this(nodeConsumer, null);
049    }
050
051    /**
052     * Creates a new postorder list generator.
053     *
054     * @since 2.0.12
055     */
056    public PostorderDependencyNodeConsumerVisitor(Consumer<DependencyNode> nodeConsumer, DependencyFilter filter) {
057        super(nodeConsumer, filter);
058        visits = new Stack<>();
059    }
060
061    @Override
062    protected boolean doVisitEnter(DependencyNode node) {
063        boolean visited = !setVisited(node);
064        visits.push(visited);
065        return !visited;
066    }
067
068    @Override
069    protected boolean doVisitLeave(DependencyNode node) {
070        Boolean visited = visits.pop();
071        if (visited) {
072            return true;
073        }
074        if (acceptNode(node)) {
075            consumeNode(node);
076        }
077        return true;
078    }
079}