/*

  * 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.Iterator;

 /**

  * <p>

  * A concrete combiner implementation that is able to construct an override

  * combination.

  * </p>

  * <p>

  * An <em>override combination</em> means that nodes in the first node

  * structure take precedence over nodes in the second, or - in other words -

  * nodes of the second structure are only added to the resulting structure if

  * they do not occure in the first one. This is especially suitable for dealing

  * with the properties of configurations that are defined in an

  * <code>override</code> section of a configuration definition file (hence the

  * name).

  * </p>

  * <p>

  * This combiner will iterate over the second node hierarchy and find all nodes

  * that are not contained in the first hierarchy; these are added to the result.

  * If a node can be found in both structures, it is checked whether a

  * combination (in a recursive way) can be constructed for the two, which will

  * then be added. Per default, nodes are combined, which occur only once in both

  * structures. This test is implemented in the <code>canCombine()</code>

  * method.

  * </p>

  * <p>

  * As is true for the <code>{@link UnionCombiner}</code>, for this combiner

  * list nodes are important. The <code>addListNode()</code> can be called to

  * declare certain nodes as list nodes. This has the effect that these nodes

  * will never be combined.

  * </p>

  *

  * @author <a

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

  * Configuration team</a>

  * @version $Id: OverrideCombiner.java 439648 2006-09-02 20:42:10Z oheger $

  * @since 1.3

  */

 public class OverrideCombiner extends NodeCombiner

 {

     /**

      * Constructs an override combination for the passed in node structures.

      *

      * @param node1 the first node

      * @param node2 the second node

      * @return the resulting combined node structure

      */

     public ConfigurationNode combine(ConfigurationNode node1,

             ConfigurationNode node2)

     {

         ViewNode result = createViewNode();

         result.setName(node1.getName());

         // Process nodes from the first structure, which override the second

         for (Iterator it = node1.getChildren().iterator(); it.hasNext();)

         {

             ConfigurationNode child = (ConfigurationNode) it.next();

             ConfigurationNode child2 = canCombine(node1, node2, child);

             if (child2 != null)

             {

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

             }

             else

             {

                 result.addChild(child);

             }

         }

         // Process nodes from the second structure, which are not contained

         // in the first structure

         for (Iterator it = node2.getChildren().iterator(); it.hasNext();)

         {

             ConfigurationNode child = (ConfigurationNode) it.next();

             if (node1.getChildrenCount(child.getName()) < 1)

             {

                 result.addChild(child);

             }

         }

         // Handle attributes and value

         addAttributes(result, node1, node2);

         result.setValue((node1.getValue() != null) ? node1.getValue() : node2

                 .getValue());

         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 (Iterator it = node2.getAttributes().iterator(); it.hasNext();)

         {

             ConfigurationNode attr = (ConfigurationNode) it.next();

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

             {

                 result.addAttribute(attr);

             }

         }

     }

     /**

      * Tests if a child node of the second node can be combined with the given

      * child node of the first node. If this is the case, the corresponding node

      * will be returned, otherwise <b>null</b>. This implementation checks

      * whether the child node occurs only once in both hierarchies and is no

      * known list node.

      *

      * @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)

     {

         if (node2.getChildrenCount(child.getName()) == 1

                 && node1.getChildrenCount(child.getName()) == 1

                 && !isListNode(child))

         {

             return (ConfigurationNode) node2.getChildren(child.getName())

                     .get(0);

         }

         else

         {

             return null;

         }

     }

 }