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.IdentityHashMap;
022import java.util.Map;
023
024import org.eclipse.aether.graph.DefaultDependencyNode;
025import org.eclipse.aether.graph.DependencyNode;
026import org.eclipse.aether.graph.DependencyVisitor;
027
028/**
029 * A dependency visitor that constructs a clone of the visited dependency graph. If such a visitor is passed into a
030 * {@link FilteringDependencyVisitor}, a sub graph can be created. This class creates shallow clones of the visited
031 * dependency nodes (via {@link DefaultDependencyNode#DefaultDependencyNode(DependencyNode)}) but clients can create a
032 * subclass and override {@link #clone(DependencyNode)} to alter the clone process.
033 */
034public class CloningDependencyVisitor implements DependencyVisitor {
035
036    private final Map<DependencyNode, DependencyNode> clones;
037
038    private final Stack<DependencyNode> parents;
039
040    private DependencyNode root;
041
042    /**
043     * Creates a new visitor that clones the visited nodes.
044     */
045    public CloningDependencyVisitor() {
046        parents = new Stack<>();
047        clones = new IdentityHashMap<>(256);
048    }
049
050    /**
051     * Gets the root node of the cloned dependency graph.
052     *
053     * @return The root node of the cloned dependency graph or {@code null}.
054     */
055    public final DependencyNode getRootNode() {
056        return root;
057    }
058
059    /**
060     * Creates a clone of the specified node.
061     *
062     * @param node The node to clone, must not be {@code null}.
063     * @return The cloned node, never {@code null}.
064     */
065    protected DependencyNode clone(DependencyNode node) {
066        return new DefaultDependencyNode(node);
067    }
068
069    @Override
070    public final boolean visitEnter(DependencyNode node) {
071        boolean recurse = true;
072
073        DependencyNode clone = clones.get(node);
074        if (clone == null) {
075            clone = clone(node);
076            clones.put(node, clone);
077        } else {
078            recurse = false;
079        }
080
081        DependencyNode parent = parents.peek();
082
083        if (parent == null) {
084            root = clone;
085        } else {
086            parent.getChildren().add(clone);
087        }
088
089        parents.push(clone);
090
091        return recurse;
092    }
093
094    @Override
095    public final boolean visitLeave(DependencyNode node) {
096        parents.pop();
097
098        return true;
099    }
100}