package org.eclipse.aether.util.graph.visitor;

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 * 
 *  http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

import org.eclipse.aether.graph.DependencyNode;

Generates a sequence of dependency nodes from a dependeny graph by traversing the graph in postorder. This visitor
visits each node exactly once regardless how many paths within the dependency graph lead to the node such that the
resulting node sequence is free of duplicates.
/**
 * Generates a sequence of dependency nodes from a dependeny graph by traversing the graph in postorder. This visitor
 * visits each node exactly once regardless how many paths within the dependency graph lead to the node such that the
 * resulting node sequence is free of duplicates.
 */
public final class PostorderNodeListGenerator
    extends AbstractDepthFirstNodeListGenerator
{

    private final Stack<Boolean> visits;

    
Creates a new postorder list generator.
/**
     * Creates a new postorder list generator.
     */
    public PostorderNodeListGenerator()
    {
        visits = new Stack<>();
    }

    @Override
    public boolean visitEnter( DependencyNode node )
    {
        boolean visited = !setVisited( node );

        visits.push( visited );

        if ( visited )
        {
            return false;
        }

        return true;
    }

    @Override
    public boolean visitLeave( DependencyNode node )
    {
        Boolean visited = visits.pop();

        if ( visited )
        {
            return true;
        }

        if ( node.getDependency() != null )
        {
            nodes.add( node );
        }

        return true;
    }

}