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.graph.DependencyNode;
024
025/**
026 * Processes dependency graph by traversing the graph in postorder. This visitor visits each node exactly once
027 * regardless how many paths within the dependency graph lead to the node such that the resulting node sequence is
028 * free of duplicates.
029 *
030 * @since TBD
031 */
032public final class PostorderDependencyNodeConsumerVisitor extends AbstractDependencyNodeConsumerVisitor {
033
034    public static final String NAME = "postOrder";
035
036    private final Stack<Boolean> visits;
037
038    /**
039     * Creates a new postorder list generator.
040     */
041    public PostorderDependencyNodeConsumerVisitor(Consumer<DependencyNode> nodeConsumer) {
042        super(nodeConsumer);
043        visits = new Stack<>();
044    }
045
046    @Override
047    public boolean visitEnter(DependencyNode node) {
048        boolean visited = !setVisited(node);
049        visits.push(visited);
050        return !visited;
051    }
052
053    @Override
054    public boolean visitLeave(DependencyNode node) {
055        Boolean visited = visits.pop();
056        if (visited) {
057            return true;
058        }
059        nodeConsumer.accept(node);
060        return true;
061    }
062}