/*

  * 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.reloading;

 import java.io.File;

 import java.net.MalformedURLException;

 import java.net.URL;

 import org.apache.commons.configuration.ConfigurationUtils;

 import org.apache.commons.configuration.FileConfiguration;

 /**

  * <p>A reloading strategy that will reload the configuration every time its

  * underlying file is changed.</p>

  * <p>This reloading strategy does not actively monitor a configuration file,

  * but is triggered by its associated configuration whenever properties are

  * accessed. It then checks the configuration file's last modification date

  * and causes a reload if this has changed.</p>

  * <p>To avoid permanent disc access on successive property lookups a refresh

  * delay can be specified. This has the effect that the configuration file's

  * last modification date is only checked once in this delay period. The default

  * value for this refresh delay is 5 seconds.</p>

  * <p>This strategy only works with FileConfiguration instances.</p>

  *

  * @author Emmanuel Bourg

  * @version $Revision: 606798 $, $Date: 2007-12-25 20:05:58 +0100 (Di, 25 Dez 2007) $

  * @since 1.1

  */

 public class FileChangedReloadingStrategy implements ReloadingStrategy

 {

     /** Constant for the jar URL protocol.*/

     private static final String JAR_PROTOCOL = "jar";

     /** Constant for the default refresh delay.*/

     private static final int DEFAULT_REFRESH_DELAY = 5000;

     /** Stores a reference to the configuration to be monitored.*/

     protected FileConfiguration configuration;

     /** The last time the configuration file was modified. */

     protected long lastModified;

     /** The last time the file was checked for changes. */

     protected long lastChecked;

     /** The minimum delay in milliseconds between checks. */

     protected long refreshDelay = DEFAULT_REFRESH_DELAY;

     /** A flag whether a reload is required.*/

     private boolean reloading;

     public void setConfiguration(FileConfiguration configuration)

     {

         this.configuration = configuration;

     }

     public void init()

     {

         updateLastModified();

     }

     public boolean reloadingRequired()

     {

         if (!reloading)

         {

             long now = System.currentTimeMillis();

             if (now > lastChecked + refreshDelay)

             {

                 lastChecked = now;

                 if (hasChanged())

                 {

                     reloading = true;

                 }

             }

         }

         return reloading;

     }

     public void reloadingPerformed()

     {

         updateLastModified();

     }

     /**

      * Return the minimal time in milliseconds between two reloadings.

      *

      * @return the refresh delay (in milliseconds)

      */

     public long getRefreshDelay()

     {

         return refreshDelay;

     }

     /**

      * Set the minimal time between two reloadings.

      *

      * @param refreshDelay refresh delay in milliseconds

      */

     public void setRefreshDelay(long refreshDelay)

     {

         this.refreshDelay = refreshDelay;

     }

     /**

      * Update the last modified time.

      */

     protected void updateLastModified()

     {

         File file = getFile();

         if (file != null)

         {

             lastModified = file.lastModified();

         }

         reloading = false;

     }

     /**

      * Check if the configuration has changed since the last time it was loaded.

      *

      * @return a flag whether the configuration has changed

      */

     protected boolean hasChanged()

     {

         File file = getFile();

         if (file == null || !file.exists())

         {

             return false;

         }

         return file.lastModified() > lastModified;

     }

     /**

      * Returns the file that is monitored by this strategy. Note that the return

      * value can be <b>null </b> under some circumstances.

      *

      * @return the monitored file

      */

     protected File getFile()

     {

         return (configuration.getURL() != null) ? fileFromURL(configuration

                 .getURL()) : configuration.getFile();

     }

     /**

      * Helper method for transforming a URL into a file object. This method

      * handles file: and jar: URLs.

      *

      * @param url the URL to be converted

      * @return the resulting file or <b>null </b>

      */

     private File fileFromURL(URL url)

     {

         if (JAR_PROTOCOL.equals(url.getProtocol()))

         {

             String path = url.getPath();

             try

             {

                 return ConfigurationUtils.fileFromURL(new URL(path.substring(0,

                         path.indexOf('!'))));

             }

             catch (MalformedURLException mex)

             {

                 return null;

             }

         }

         else

         {

             return ConfigurationUtils.fileFromURL(url);

         }

     }

 }