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