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 that performs a merge from two passed in node
029 * 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     * Checks whether the attributes of the passed in node are compatible.
046     *
047     * @param attrs1 the attributes of the first node
048     * @param node the 2nd node
049     * @return a flag whether these nodes can be combined regarding their attributes
050     */
051    private static boolean matchAttributes(final Map<String, Object> attrs1, final ImmutableNode node) {
052        final Map<String, Object> attrs2 = node.getAttributes();
053        for (final Map.Entry<String, Object> e : attrs1.entrySet()) {
054            if (attrs2.containsKey(e.getKey()) && !Objects.equals(e.getValue(), attrs2.get(e.getKey()))) {
055                return false;
056            }
057        }
058        return true;
059    }
060
061    /**
062     * Handles the attributes during a combination process. First all attributes of the first node will be added to the
063     * result. Then all attributes of the second node, which are not contained in the first node, will also be added.
064     *
065     * @param result the builder for the resulting node
066     * @param node1 the first node
067     * @param node2 the second node
068     */
069    protected void addAttributes(final ImmutableNode.Builder result, final ImmutableNode node1, final ImmutableNode node2) {
070        final Map<String, Object> attributes = new HashMap<>(node1.getAttributes());
071        node2.getAttributes().forEach(attributes::putIfAbsent);
072        result.addAttributes(attributes);
073    }
074
075    /**
076     * Tests if the first node can be combined with the second node. A node can only be combined if its attributes are all
077     * present in the second node and they all have the same value.
078     *
079     * @param node2 the second node
080     * @param child the child node (of the first node)
081     * @param children2 the children of the 2nd node
082     * @return a child of the second node, with which a combination is possible
083     */
084    protected ImmutableNode canCombine(final ImmutableNode node2, final ImmutableNode child, final List<ImmutableNode> children2) {
085        final Map<String, Object> attrs1 = child.getAttributes();
086        final List<ImmutableNode> nodes = new ArrayList<>();
087
088        final List<ImmutableNode> children = HANDLER.getChildren(node2, child.getNodeName());
089        children.forEach(node -> {
090            if (matchAttributes(attrs1, node)) {
091                nodes.add(node);
092            }
093        });
094
095        if (nodes.size() == 1) {
096            return nodes.get(0);
097        }
098        if (nodes.size() > 1 && !isListNode(child)) {
099            nodes.forEach(children2::remove);
100        }
101
102        return null;
103    }
104
105    /**
106     * Combines the given nodes to a new union node.
107     *
108     * @param node1 the first source node
109     * @param node2 the second source node
110     * @return the union node
111     */
112
113    @Override
114    public ImmutableNode combine(final ImmutableNode node1, final ImmutableNode node2) {
115        final ImmutableNode.Builder result = new ImmutableNode.Builder();
116        result.name(node1.getNodeName());
117        result.value(node1.getValue());
118        addAttributes(result, node1, node2);
119
120        // Check if nodes can be combined
121        final List<ImmutableNode> children2 = new LinkedList<>(node2.getChildren());
122        node1.forEach(child1 -> {
123            final ImmutableNode child2 = canCombine(node2, child1, children2);
124            if (child2 != null) {
125                result.addChild(combine(child1, child2));
126                children2.remove(child2);
127            } else {
128                result.addChild(child1);
129            }
130        });
131
132        // Add remaining children of node 2
133        children2.forEach(result::addChild);
134        return result.create();
135    }
136}