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 * @since 1.7
042 */
043public class MergeCombiner extends NodeCombiner
044{
045    /**
046     * Combines the given nodes to a new union node.
047     *
048     * @param node1 the first source node
049     * @param node2 the second source node
050     * @return the union node
051     */
052
053    @Override
054    public ImmutableNode combine(final ImmutableNode node1, final ImmutableNode node2)
055    {
056        final ImmutableNode.Builder result = new ImmutableNode.Builder();
057        result.name(node1.getNodeName());
058        result.value(node1.getValue());
059        addAttributes(result, node1, node2);
060
061        // Check if nodes can be combined
062        final List<ImmutableNode> children2 = new LinkedList<>(node2.getChildren());
063        for (final ImmutableNode child1 : node1.getChildren())
064        {
065            final ImmutableNode child2 = canCombine(node2, child1, children2);
066            if (child2 != null)
067            {
068                result.addChild(combine(child1, child2));
069                children2.remove(child2);
070            }
071            else
072            {
073                result.addChild(child1);
074            }
075        }
076
077        // Add remaining children of node 2
078        for (final ImmutableNode c : children2)
079        {
080            result.addChild(c);
081        }
082        return result.create();
083    }
084
085    /**
086     * Handles the attributes during a combination process. First all attributes
087     * of the first node will be added to the result. Then all attributes of the
088     * second node, which are not contained in the first node, will also be
089     * added.
090     *
091     * @param result the builder for the resulting node
092     * @param node1 the first node
093     * @param node2 the second node
094     */
095    protected void addAttributes(final ImmutableNode.Builder result, final ImmutableNode node1,
096            final ImmutableNode node2)
097    {
098        final Map<String, Object> attributes = new HashMap<>();
099        attributes.putAll(node1.getAttributes());
100        for (final Map.Entry<String, Object> e : node2.getAttributes().entrySet())
101        {
102            if (!attributes.containsKey(e.getKey()))
103            {
104                attributes.put(e.getKey(), e.getValue());
105            }
106        }
107        result.addAttributes(attributes);
108    }
109
110    /**
111     * Tests if the first node can be combined with the second node. A node can
112     * only be combined if its attributes are all present in the second node and
113     * they all have the same value.
114     *
115     * @param node2 the second node
116     * @param child the child node (of the first node)
117     * @param children2 the children of the 2nd node
118     * @return a child of the second node, with which a combination is possible
119     */
120    protected ImmutableNode canCombine(final ImmutableNode node2,
121            final ImmutableNode child, final List<ImmutableNode> children2)
122    {
123        final Map<String, Object> attrs1 = child.getAttributes();
124        final List<ImmutableNode> nodes = new ArrayList<>();
125
126        final List<ImmutableNode> children =
127                HANDLER.getChildren(node2, child.getNodeName());
128        for (final ImmutableNode node : children)
129        {
130            if (matchAttributes(attrs1, node))
131            {
132                nodes.add(node);
133            }
134        }
135
136        if (nodes.size() == 1)
137        {
138            return nodes.get(0);
139        }
140        if (nodes.size() > 1 && !isListNode(child))
141        {
142            for (final ImmutableNode node : nodes)
143            {
144                children2.remove(node);
145            }
146        }
147
148        return null;
149    }
150
151    /**
152     * Checks whether the attributes of the passed in node are compatible.
153     *
154     * @param attrs1 the attributes of the first node
155     * @param node the 2nd node
156     * @return a flag whether these nodes can be combined regarding their
157     *         attributes
158     */
159    private static boolean matchAttributes(final Map<String, Object> attrs1,
160            final ImmutableNode node)
161    {
162        final Map<String, Object> attrs2 = node.getAttributes();
163        for (final Map.Entry<String, Object> e : attrs1.entrySet())
164        {
165            if (attrs2.containsKey(e.getKey())
166                    && !Objects
167                            .equals(e.getValue(), attrs2.get(e.getKey())))
168            {
169                return false;
170            }
171        }
172        return true;
173    }
174}