/*
    * Copyright 2000-2004 The Apache Software Foundation.
    * 
    * Licensed 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.jetspeed.portal.expire;
  
  //jetspeed stuff
  import org.apache.jetspeed.cache.disk.DiskCacheEntry;
  import org.apache.jetspeed.cache.disk.DiskCacheUtils;
  import org.apache.jetspeed.cache.disk.JetspeedDiskCache;
  import org.apache.jetspeed.services.logging.JetspeedLogFactoryService;
  import org.apache.jetspeed.services.logging.JetspeedLogger;
  
  //java stuff
  import java.io.IOException;
  import java.io.Serializable;
  
  
  /***
  A generic class for watching a file and determining if it has changed.
  
  @author <a href="mailto:burton@apache.org">Kevin A. Burton</a>
  @version $Id: FileWatcher.java,v 1.16 2004/02/23 03:24:40 jford Exp $
  */
  public class FileWatcher implements Serializable
  {
  
      /***
       * Static initialization of the logger for this class
       */    
      private static final JetspeedLogger logger = JetspeedLogFactoryService.getLogger(FileWatcher.class.getName());    
      
      //BEGIN Exception index
  
      public static final String EXCEPTION_URL_NOT_NULL = 
          "URL can NOT be null here.";
      
      public static final String EXCEPTION_URL_NOT_IN_CACHE = 
          "The URL you specified within the disk cache does not exist: ";
      
      
      //END Exception index    
      
      /***
      The URL on which this FileWatchExpire is based.
      */
      private String url = "";
  
      /***
      The last time this files URL has been modified on disk.
      */
      private long lastModified = 0;
  
      /***
      The object that relies on this FileWatcher
      */
      private String parent = "";
  
      /***
      Create a FileWatcher with no parent info.
      
      @see #FileWatcher( String, String )
      
      @author <a href="mailto:burton@apache.org">Kevin A. Burton</a>
      @version $Id: FileWatcher.java,v 1.16 2004/02/23 03:24:40 jford Exp $
      */
      public FileWatcher( String url ) throws IOException {
          this( url, null );
      }
                              
      /***
      Create a new FileWatcher to watch the given URL.
      
      @author <a href="mailto:burton@apache.org">Kevin A. Burton</a>
      @version $Id: FileWatcher.java,v 1.16 2004/02/23 03:24:40 jford Exp $
      */
      public FileWatcher( String url,
                          String parent ) throws IOException {
          
          if ( url == null ) {
              throw new IOException( EXCEPTION_URL_NOT_NULL );
          }
  
          if ( DiskCacheUtils.isRemote( url ) &&
               DiskCacheUtils.isCached( url ) == false ) {
              
              throw new IOException( EXCEPTION_URL_NOT_IN_CACHE + url );
         }
 
         //Try to set last modified when creating FileWatcher objet
         try {
             this.lastModified = JetspeedDiskCache.getInstance().getEntry( url ).
                                                             getLastModified();
         } catch (Throwable e) 
         {
             logger.error( "Unable to set last modified on url " + url, e );
         }
         
         this.url = url;
         this.parent = parent;
     }
     
     /***
     Return true if the URL on which this is based has changed.
 
     @author <a href="mailto:burton@apache.org">Kevin A. Burton</a>
     @version $Id: FileWatcher.java,v 1.16 2004/02/23 03:24:40 jford Exp $
     */
     public boolean hasChanged() {
 
         try {
 
             //initially set the lastModified data
             if ( this.lastModified == 0 ) {
             
                 DiskCacheEntry entry = JetspeedDiskCache.getInstance().getEntry( url );
                 
                 this.lastModified = entry.getLastModified();
 
                 return false;
             
             }
 
             //the recent modification... if there was one. otherwise it will 
             // == this.lastModified
             long recent = JetspeedDiskCache.getInstance()
                 .getEntry( url ).getLastModified();
 
             // 0 means always modified
             if ( recent == 0 || 
                 this.lastModified < recent ) {
                    
                 if ( logger.isInfoEnabled() )
                 {
                     String message = "";
 
                     if ( this.parent != null ) {
                         message = this.parent + ":  ";
                     }
 
                     message += "REFRESH: Expiring Portlet because it's URL has been modified on disk -> " + url;
 
                     logger.info( message );
                 }
                 return true;
             } 
             
         } catch ( IOException e ) {
             logger.error("Exception",  e );
             return false;
         }
         
         //default should be to not expire.  This is set if the URL is null
         return false;        
         
     }
     
 }