001package org.eclipse.aether.util.graph.visitor;
002
003/*
004 * Licensed to the Apache Software Foundation (ASF) under one
005 * or more contributor license agreements.  See the NOTICE file
006 * distributed with this work for additional information
007 * regarding copyright ownership.  The ASF licenses this file
008 * to you under the Apache License, Version 2.0 (the
009 * "License"); you may not use this file except in compliance
010 * with the License.  You may obtain a copy of the License at
011 * 
012 *  http://www.apache.org/licenses/LICENSE-2.0
013 * 
014 * Unless required by applicable law or agreed to in writing,
015 * software distributed under the License is distributed on an
016 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
017 * KIND, either express or implied.  See the License for the
018 * specific language governing permissions and limitations
019 * under the License.
020 */
021
022import java.util.IdentityHashMap;
023import java.util.Map;
024import static java.util.Objects.requireNonNull;
025
026import org.eclipse.aether.graph.DependencyNode;
027import org.eclipse.aether.graph.DependencyVisitor;
028
029/**
030 * A dependency visitor that delegates to another visitor if a node hasn't been visited before. In other words, this
031 * visitor provides a tree-view of a dependency graph which generally can have multiple paths to the same node or even
032 * cycles.
033 */
034public final class TreeDependencyVisitor
035    implements DependencyVisitor
036{
037
038    private final Map<DependencyNode, Object> visitedNodes;
039
040    private final DependencyVisitor visitor;
041
042    private final Stack<Boolean> visits;
043
044    /**
045     * Creates a new visitor that delegates to the specified visitor.
046     *
047     * @param visitor The visitor to delegate to, must not be {@code null}.
048     */
049    public TreeDependencyVisitor( DependencyVisitor visitor )
050    {
051        this.visitor = requireNonNull( visitor, "dependency visitor delegate cannot be null" );
052        visitedNodes = new IdentityHashMap<DependencyNode, Object>( 512 );
053        visits = new Stack<Boolean>();
054    }
055
056    public boolean visitEnter( DependencyNode node )
057    {
058        boolean visited = visitedNodes.put( node, Boolean.TRUE ) != null;
059
060        visits.push( visited );
061
062        if ( visited )
063        {
064            return false;
065        }
066
067        return visitor.visitEnter( node );
068    }
069
070    public boolean visitLeave( DependencyNode node )
071    {
072        Boolean visited = visits.pop();
073
074        if ( visited )
075        {
076            return true;
077        }
078
079        return visitor.visitLeave( node );
080    }
081
082}