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 org.eclipse.aether.graph.DependencyNode;
022
023/**
024 * Generates a sequence of dependency nodes from a dependeny graph by traversing the graph in postorder. This visitor
025 * visits each node exactly once regardless how many paths within the dependency graph lead to the node such that the
026 * resulting node sequence is free of duplicates.
027 */
028public final class PostorderNodeListGenerator extends AbstractDepthFirstNodeListGenerator {
029
030    private final Stack<Boolean> visits;
031
032    /**
033     * Creates a new postorder list generator.
034     */
035    public PostorderNodeListGenerator() {
036        visits = new Stack<>();
037    }
038
039    @Override
040    public boolean visitEnter(DependencyNode node) {
041        boolean visited = !setVisited(node);
042
043        visits.push(visited);
044
045        return !visited;
046    }
047
048    @Override
049    public boolean visitLeave(DependencyNode node) {
050        Boolean visited = visits.pop();
051
052        if (visited) {
053            return true;
054        }
055
056        if (node.getDependency() != null) {
057            nodes.add(node);
058        }
059
060        return true;
061    }
062}