/**
    * Copyright 2005-2012 The Kuali Foundation
    *
    * Licensed under the Educational Community 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.opensource.org/licenses/ecl2.php
    *
   * 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.kuali.rice.krad.datadictionary;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  
  import java.io.IOException;
  import java.net.URL;
  import java.util.LinkedList;
  import java.util.Map;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.Executors;
  import java.util.concurrent.ScheduledExecutorService;
  import java.util.concurrent.TimeUnit;
  import java.util.zip.CRC32;
  import java.util.zip.CheckedInputStream;
  
  /**
   * This is a description of what this class does - gilesp don't forget to fill this in.
   *
   * @author Kuali Rice Team (rice.collab@kuali.org)
   *
   */
  public class URLMonitor {
      private static final Log LOG = LogFactory.getLog(URLMonitor.class);
  
      private final LinkedList<URLContentChangedListener> listeners = new LinkedList<URLContentChangedListener>();
      private final Map<URL, Long> resourceMap = new ConcurrentHashMap();
      private final int reloadIntervalMilliseconds;
      private final ScheduledExecutorService scheduler = Executors.newScheduledThreadPool(1);
  
  
      public URLMonitor(int reloadIntervalMilliseconds) {
          this.reloadIntervalMilliseconds = reloadIntervalMilliseconds;
      }
  
      public synchronized void addListener(URLContentChangedListener listener) {
  
          listeners.add(listener);
  
          if (listeners.size() == 1) {
              scheduler.scheduleAtFixedRate(urlPoller,
  				reloadIntervalMilliseconds, reloadIntervalMilliseconds, TimeUnit.MILLISECONDS);
          }
      }
  
      public void addURI(URL zipUrl) {
  
          resourceMap.put(zipUrl, getCRC(zipUrl));
      }
  
      private Long getCRC(URL zipUrl) {
          Long result = -1l;
          try {
              CRC32 crc = new CRC32();
              CheckedInputStream cis = new CheckedInputStream(zipUrl.openStream(), crc);
  
              byte[] buffer = new byte[1024];
              int length;
  
              //read the entry from zip file and extract it to disk
              while( (length = cis.read(buffer)) > 0);
  
              cis.close();
  
              result = crc.getValue();
          } catch (IOException e) {
              LOG.warn("Unable to calculate CRC, resource doesn't exist?", e);
          }
          return result;
      }
  
      private final Runnable urlPoller = new Runnable() {
  
          @Override
          public void run() {
              for (Map.Entry<URL, Long> entry : resourceMap.entrySet()) {
                  Long crc = getCRC(entry.getKey());
  
                  if (!entry.getValue().equals(crc)) {
                      entry.setValue(crc);
                      for (URLContentChangedListener listener : listeners) {
                          listener.urlContentChanged(entry.getKey());
                      }
                  }
             }
         }
     };
 
     public static interface URLContentChangedListener {
           public void urlContentChanged(URL url);
     }
 }