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 org.eclipse.aether.graph.DependencyFilter;
023import org.eclipse.aether.graph.DependencyNode;
024import org.eclipse.aether.graph.DependencyVisitor;
025
026/**
027 * A dependency visitor that delegates to another visitor if nodes match a filter. Note that in case of a mismatching
028 * node, the children of that node are still visisted and presented to the filter.
029 */
030public final class FilteringDependencyVisitor
031    implements DependencyVisitor
032{
033
034    private final DependencyFilter filter;
035
036    private final DependencyVisitor visitor;
037
038    private final Stack<Boolean> accepts;
039
040    private final Stack<DependencyNode> parents;
041
042    /**
043     * Creates a new visitor that delegates traversal of nodes matching the given filter to the specified visitor.
044     * 
045     * @param visitor The visitor to delegate to, must not be {@code null}.
046     * @param filter The filter to apply, may be {@code null} to not filter.
047     */
048    public FilteringDependencyVisitor( DependencyVisitor visitor, DependencyFilter filter )
049    {
050        if ( visitor == null )
051        {
052            throw new IllegalArgumentException( "dependency visitor not specified" );
053        }
054        this.visitor = visitor;
055        this.filter = filter;
056        this.accepts = new Stack<Boolean>();
057        this.parents = new Stack<DependencyNode>();
058    }
059
060    /**
061     * Gets the visitor to which this visitor delegates to.
062     * 
063     * @return The visitor being delegated to, never {@code null}.
064     */
065    public DependencyVisitor getVisitor()
066    {
067        return visitor;
068    }
069
070    /**
071     * Gets the filter being applied before delegation.
072     * 
073     * @return The filter being applied or {@code null} if none.
074     */
075    public DependencyFilter getFilter()
076    {
077        return filter;
078    }
079
080    public boolean visitEnter( DependencyNode node )
081    {
082        boolean accept = filter == null || filter.accept( node, parents );
083
084        accepts.push( accept );
085
086        parents.push( node );
087
088        if ( accept )
089        {
090            return visitor.visitEnter( node );
091        }
092        else
093        {
094            return true;
095        }
096    }
097
098    public boolean visitLeave( DependencyNode node )
099    {
100        parents.pop();
101
102        Boolean accept = accepts.pop();
103
104        if ( accept )
105        {
106            return visitor.visitLeave( node );
107        }
108        else
109        {
110            return true;
111        }
112    }
113
114}