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 */
033public final class PostorderDependencyNodeConsumerVisitor extends AbstractDependencyNodeConsumerVisitor {
034
035    public static final String NAME = ConfigurationProperties.REPOSITORY_SYSTEM_DEPENDENCY_VISITOR_POSTORDER;
036
037    private final Stack<Boolean> visits;
038
039    /**
040     * Creates a new postorder list generator.
041     */
042    public PostorderDependencyNodeConsumerVisitor(Consumer<DependencyNode> nodeConsumer) {
043        super(nodeConsumer);
044        visits = new Stack<>();
045    }
046
047    @Override
048    public boolean visitEnter(DependencyNode node) {
049        boolean visited = !setVisited(node);
050        visits.push(visited);
051        return !visited;
052    }
053
054    @Override
055    public boolean visitLeave(DependencyNode node) {
056        Boolean visited = visits.pop();
057        if (visited) {
058            return true;
059        }
060        nodeConsumer.accept(node);
061        return true;
062    }
063}