/*

  * 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;

 import java.util.ArrayList;

 import java.util.Collection;

 import java.util.Collections;

 import java.util.HashSet;

 import java.util.Iterator;

 import java.util.List;

 import java.util.Set;

 /**

  * <p>A base class for converters that transform a normal configuration

  * object into a hierarchical configuration.</p>

  * <p>This class provides a default mechanism for iterating over the keys in a

  * configuration and to throw corresponding element start and end events. By

  * handling these events a hierarchy can be constructed that is equivalent to

  * the keys in the original configuration.</p>

  * <p>Concrete sub classes will implement event handlers that generate SAX

  * events for XML processing or construct a

  * <code>HierarchicalConfiguration</code> root node. All in all with this class

  * it is possible to treat a default configuration as if it was a hierarchical

  * configuration, which can be sometimes useful.</p>

  * @see HierarchicalConfiguration

  *

  * @author <a href="mailto:oliver.heger@t-online.de">Oliver Heger</a>

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

  */

 abstract class HierarchicalConfigurationConverter

 {

     /**

      * Processes the specified configuration object. This method implements

      * the iteration over the configuration's keys. All defined keys are

      * translated into a set of element start and end events represented by

      * calls to the <code>elementStart()</code> and

      * <code>elementEnd()</code> methods.

      *

      * @param config the configuration to be processed

      */

     public void process(Configuration config)

     {

         if (config != null)

         {

             ConfigurationKey keyEmpty = new ConfigurationKey();

             ConfigurationKey keyLast = keyEmpty;

             Set keySet = new HashSet();

             for (Iterator it = config.getKeys(); it.hasNext();)

             {

                 String key = (String) it.next();

                 if (keySet.contains(key))

                 {

                     // this key has already been processed by openElements

                     continue;

                 }

                 ConfigurationKey keyAct = new ConfigurationKey(key);

                 closeElements(keyLast, keyAct);

                 String elem = openElements(keyLast, keyAct, config, keySet);

                 fireValue(elem, config.getProperty(key));

                 keyLast = keyAct;

             }

             // close all open

             closeElements(keyLast, keyEmpty);

         }

     }

     /**

      * An event handler method that is called when an element starts.

      * Concrete sub classes must implement it to perform a proper event

      * handling.

      *

      * @param name the name of the new element

      * @param value the element's value; can be <b>null</b> if the element

      * does not have any value

      */

     protected abstract void elementStart(String name, Object value);

     /**

      * An event handler method that is called when an element ends. For each

      * call of <code>elementStart()</code> there will be a corresponding call

      * of this method. Concrete sub classes must implement it to perform a

      * proper event handling.

      *

      * @param name the name of the ending element

      */

     protected abstract void elementEnd(String name);

     /**

      * Fires all necessary element end events for the specified keys. This

      * method is called for each key obtained from the configuration to be

      * converted. It calculates the common part of the actual and the last

      * processed key and thus determines how many elements must be

      * closed.

      *

      * @param keyLast the last processed key

      * @param keyAct the actual key

      */

     protected void closeElements(ConfigurationKey keyLast, ConfigurationKey keyAct)

     {

         ConfigurationKey keyDiff = keyAct.differenceKey(keyLast);

         Iterator it = reverseIterator(keyDiff);

         if (it.hasNext())

         {

             // Skip first because it has already been closed by fireValue()

             it.next();

         }

         while (it.hasNext())

         {

             elementEnd((String) it.next());

         }

     }

     /**

      * Helper method for determining a reverse iterator for the specified key.

      * This implementation returns an iterator that returns the parts of the

      * given key in reverse order, ignoring indices.

      *

      * @param key the key

      * @return a reverse iterator for the parts of this key

      */

     protected Iterator reverseIterator(ConfigurationKey key)

     {

         List list = new ArrayList();

         for (ConfigurationKey.KeyIterator it = key.iterator(); it.hasNext();)

         {

             list.add(it.nextKey());

         }

         Collections.reverse(list);

         return list.iterator();

     }

     /**

      * Fires all necessary element start events for the specified key. This

      * method is called for each key obtained from the configuration to be

      * converted. It ensures that all elements "between" the last key and the

      * actual key are opened and their values are set.

      *

      * @param keyLast the last processed key

      * @param keyAct the actual key

      * @param config the configuration to process

      * @param keySet the set with the processed keys

      * @return the name of the last element on the path

      */

     protected String openElements(ConfigurationKey keyLast, ConfigurationKey keyAct, Configuration config, Set keySet)

     {

         ConfigurationKey.KeyIterator it = keyLast.differenceKey(keyAct).iterator();

         ConfigurationKey k = keyLast.commonKey(keyAct);

         for (it.nextKey(); it.hasNext(); it.nextKey())

         {

             k.append(it.currentKey(true));

             elementStart(it.currentKey(true), config.getProperty(k.toString()));

             keySet.add(k.toString());

         }

         return it.currentKey(true);

     }

     /**

      * Fires all necessary element start events with the actual element values.

      * This method is called for each key obtained from the configuration to be

      * processed with the last part of the key as argument. The value can be

      * either a single value or a collection.

      *

      * @param name the name of the actual element

      * @param value the element's value

      */

     protected void fireValue(String name, Object value)

     {

         if (value != null && value instanceof Collection)

         {

             for (Iterator it = ((Collection) value).iterator(); it.hasNext();)

             {

                 fireValue(name, it.next());

             }

         }

         else

         {

             elementStart(name, value);

             elementEnd(name);

         }

     }

 }