001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *     http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.configuration2.tree;
018
019import java.util.ArrayList;
020import java.util.HashMap;
021import java.util.LinkedList;
022import java.util.List;
023import java.util.Map;
024import java.util.Objects;
025
026/**
027 * <p>
028 * A specialized implementation of the {@code NodeCombiner} interface
029 * that performs a merge from two passed in node hierarchies.
030 * </p>
031 * <p>
032 * This combiner performs the merge using a few rules:
033 * </p>
034 * <ol>
035 * <li>Nodes can be merged when attributes that appear in both have the same value.</li>
036 * <li>Only a single node in the second file is considered a match to the node in the first file.</li>
037 * <li>Attributes in nodes that match are merged.
038 * <li>Nodes in both files that do not match are added to the result.</li>
039 * </ol>
040 *
041 * @version $Id: MergeCombiner.java 1842194 2018-09-27 22:24:23Z ggregory $
042 * @since 1.7
043 */
044public class MergeCombiner extends NodeCombiner
045{
046    /**
047     * Combines the given nodes to a new union node.
048     *
049     * @param node1 the first source node
050     * @param node2 the second source node
051     * @return the union node
052     */
053
054    @Override
055    public ImmutableNode combine(final ImmutableNode node1, final ImmutableNode node2)
056    {
057        final ImmutableNode.Builder result = new ImmutableNode.Builder();
058        result.name(node1.getNodeName());
059        result.value(node1.getValue());
060        addAttributes(result, node1, node2);
061
062        // Check if nodes can be combined
063        final List<ImmutableNode> children2 = new LinkedList<>(node2.getChildren());
064        for (final ImmutableNode child1 : node1.getChildren())
065        {
066            final ImmutableNode child2 = canCombine(node2, child1, children2);
067            if (child2 != null)
068            {
069                result.addChild(combine(child1, child2));
070                children2.remove(child2);
071            }
072            else
073            {
074                result.addChild(child1);
075            }
076        }
077
078        // Add remaining children of node 2
079        for (final ImmutableNode c : children2)
080        {
081            result.addChild(c);
082        }
083        return result.create();
084    }
085
086    /**
087     * Handles the attributes during a combination process. First all attributes
088     * of the first node will be added to the result. Then all attributes of the
089     * second node, which are not contained in the first node, will also be
090     * added.
091     *
092     * @param result the builder for the resulting node
093     * @param node1 the first node
094     * @param node2 the second node
095     */
096    protected void addAttributes(final ImmutableNode.Builder result, final ImmutableNode node1,
097            final ImmutableNode node2)
098    {
099        final Map<String, Object> attributes = new HashMap<>();
100        attributes.putAll(node1.getAttributes());
101        for (final Map.Entry<String, Object> e : node2.getAttributes().entrySet())
102        {
103            if (!attributes.containsKey(e.getKey()))
104            {
105                attributes.put(e.getKey(), e.getValue());
106            }
107        }
108        result.addAttributes(attributes);
109    }
110
111    /**
112     * Tests if the first node can be combined with the second node. A node can
113     * only be combined if its attributes are all present in the second node and
114     * they all have the same value.
115     *
116     * @param node2 the second node
117     * @param child the child node (of the first node)
118     * @param children2 the children of the 2nd node
119     * @return a child of the second node, with which a combination is possible
120     */
121    protected ImmutableNode canCombine(final ImmutableNode node2,
122            final ImmutableNode child, final List<ImmutableNode> children2)
123    {
124        final Map<String, Object> attrs1 = child.getAttributes();
125        final List<ImmutableNode> nodes = new ArrayList<>();
126
127        final List<ImmutableNode> children =
128                HANDLER.getChildren(node2, child.getNodeName());
129        for (final ImmutableNode node : children)
130        {
131            if (matchAttributes(attrs1, node))
132            {
133                nodes.add(node);
134            }
135        }
136
137        if (nodes.size() == 1)
138        {
139            return nodes.get(0);
140        }
141        if (nodes.size() > 1 && !isListNode(child))
142        {
143            for (final ImmutableNode node : nodes)
144            {
145                children2.remove(node);
146            }
147        }
148
149        return null;
150    }
151
152    /**
153     * Checks whether the attributes of the passed in node are compatible.
154     *
155     * @param attrs1 the attributes of the first node
156     * @param node the 2nd node
157     * @return a flag whether these nodes can be combined regarding their
158     *         attributes
159     */
160    private static boolean matchAttributes(final Map<String, Object> attrs1,
161            final ImmutableNode node)
162    {
163        final Map<String, Object> attrs2 = node.getAttributes();
164        for (final Map.Entry<String, Object> e : attrs1.entrySet())
165        {
166            if (attrs2.containsKey(e.getKey())
167                    && !Objects
168                            .equals(e.getValue(), attrs2.get(e.getKey())))
169            {
170                return false;
171            }
172        }
173        return true;
174    }
175}