/*

  * Licensed to the Apache Software Foundation (ASF) under one or more

  * contributor license agreements.  See the NOTICE file distributed with

  * this work for additional information regarding copyright ownership.

  * The ASF licenses this file to You under the Apache License, Version 2.0

  * (the "License"); you may not use this file except in compliance with

  * the License.  You may obtain a copy of the License at

  *

  *     http://www.apache.org/licenses/LICENSE-2.0

  *

  * Unless required by applicable law or agreed to in writing, software

  * distributed under the License is distributed on an "AS IS" BASIS,

  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

  * See the License for the specific language governing permissions and

  * limitations under the License.

  */

 package org.apache.commons.configuration.tree;

 import java.util.ArrayList;

 import java.util.Iterator;

 import java.util.LinkedList;

 import java.util.List;

 /**

  * <p>

  * A specialized implementation of the {@code NodeCombiner} interface

  * that performs a merge from two passed in node hierarchies.

  * </p>

  * <p>

  * This combiner performs the merge using a few rules:

  * <ol>

  * <li>Nodes can be merged when attributes that appear in both have the same value.</li>

  * <li>Only a single node in the second file is considered a match to the node in the first file.</li>

  * <li>Attributes in nodes that match are merged.

  * <li>Nodes in both files that do not match are added to the result.</li>

  * </ol>

  * </p>

  *

  * @author <a

  * href="http://commons.apache.org/configuration/team-list.html">Commons

  * Configuration team</a>

  * @version $Id: MergeCombiner.java 1301991 2012-03-17 20:18:02Z sebb $

  * @since 1.7

  */

 public class MergeCombiner extends NodeCombiner

 {

     /**

      * Combines the given nodes to a new union node.

      *

      * @param node1 the first source node

      * @param node2 the second source node

      * @return the union node

      */

     @Override

     public ConfigurationNode combine(ConfigurationNode node1, ConfigurationNode node2)

     {

         ViewNode result = createViewNode();

         result.setName(node1.getName());

         result.setValue(node1.getValue());

         addAttributes(result, node1, node2);

         // Check if nodes can be combined

         List<ConfigurationNode> children2 = new LinkedList<ConfigurationNode>(node2.getChildren());

         for (ConfigurationNode child1 : node1.getChildren())

         {

             ConfigurationNode child2 = canCombine(node1, node2, child1, children2);

             if (child2 != null)

             {

                 result.addChild(combine(child1, child2));

                 children2.remove(child2);

             }

             else

             {

                 result.addChild(child1);

             }

         }

         // Add remaining children of node 2

         for (ConfigurationNode c : children2)

         {

             result.addChild(c);

         }

         return result;

     }

     /**

      * Handles the attributes during a combination process. First all attributes

      * of the first node will be added to the result. Then all attributes of the

      * second node, which are not contained in the first node, will also be

      * added.

      *

      * @param result the resulting node

      * @param node1 the first node

      * @param node2 the second node

      */

     protected void addAttributes(ViewNode result, ConfigurationNode node1,

             ConfigurationNode node2)

     {

         result.appendAttributes(node1);

         for (ConfigurationNode attr : node2.getAttributes())

         {

             if (node1.getAttributeCount(attr.getName()) == 0)

             {

                 result.addAttribute(attr);

             }

         }

     }

     /**

      * Tests if the first node can be combined with the second node. A node can

      * only be combined if its attributes are all present in the second node and

      * they all have the same value.

      *

      * @param node1 the first node

      * @param node2 the second node

      * @param child the child node (of the first node)

      * @return a child of the second node, with which a combination is possible

      */

     protected ConfigurationNode canCombine(ConfigurationNode node1,

             ConfigurationNode node2, ConfigurationNode child, List<ConfigurationNode> children2)

     {

         List<ConfigurationNode> attrs1 = child.getAttributes();

         List<ConfigurationNode> nodes = new ArrayList<ConfigurationNode>();

         List<ConfigurationNode> children = node2.getChildren(child.getName());

         Iterator<ConfigurationNode> it = children.iterator();

         while (it.hasNext())

         {

             ConfigurationNode node = it.next();

             Iterator<ConfigurationNode> iter = attrs1.iterator();

             while (iter.hasNext())

             {

                 ConfigurationNode attr1 = iter.next();

                 List<ConfigurationNode> list2 = node.getAttributes(attr1.getName());

                 if (list2.size() == 1

                     && !attr1.getValue().equals(list2.get(0).getValue()))

                 {

                     node = null;

                     break;

                 }

             }

             if (node != null)

             {

                 nodes.add(node);

             }

         }

         if (nodes.size() == 1)

         {

             return nodes.get(0);

         }

         if (nodes.size() > 1 && !isListNode(child))

         {

             Iterator<ConfigurationNode> iter = nodes.iterator();

             while (iter.hasNext())

             {

                 children2.remove(iter.next());

             }

         }

         return null;

     }

 }