package uk.ac.vamsas.client.simpleclient;



public abstract class WatcherElement {

  private static org.apache.commons.logging.Log log = org.apache.commons.logging.LogFactory.getLog(VamsasFileWatcherElement.class);
  protected FileWatcher watcher = null;
  protected WatcherCallBack handler = null;
  /**
   * set this to false to stop the thread
   */
  private boolean watchForChange = true;
  /**
   * true when the handler is being called for this watcher
   */
  protected boolean handlerCalled = false;

  public WatcherElement(WatcherCallBack handler) {
    this.handler = handler;
  }
  /**
   * will instruct watcher to stop and wait around for one WATCH_SLEEP
   * before returning. If no thread is running then it returns immediately.
   */
  public void haltWatch() {
    if (log.isDebugEnabled())
      log.debug("haltWatch on "+watcher.getSubject());
    // set the flag to skip this watch element.
    watchForChange=false;
    endWatch();
    // watcher=null;
    
  }
  /**
   * called by haltWatch before 
   * clearing the FileWatcher reference.
   *
   */
  protected abstract void endWatch();
  /**
   * called to generate the watcher object
   * by enableWatch and in doWatch
   *
   */
  protected abstract void initWatch();
  /**
   * implemented for debug information purposes.
   * @return Informative string about what the watcher is watching
   */
  protected abstract String getSubject();
  /**
   * must be called by implementations of 
   * enablewatch
   */
  protected void enableWatch() {
    watchForChange=true;
    initWatch();
    if (log.isDebugEnabled())
      log.debug("enableWatch returning on "+getSubject());
  }

  /**
   * Originally from the uk.ac.vamsas.test.simpleclient.ArchiveClient method
   * @return true if the handler was called for a changeEvent
   */
  public boolean doWatch() {
    if (!watchForChange || handler==null)
      return false;
    if (watcher==null)
      initWatch(); // somehow not done the first time
    handlerCalled=false;
    Lock doclock=null;
    try {
      doclock=watcher.getChangedState();
    } catch (Exception e) {
      log.error("Whilst watching "+watcher.getSubject(), e);
    }
    if (doclock==null)
      return false;
    handlerCalled=true;
    if (log.isDebugEnabled())
      log.debug("Triggering watchEvent for change on "+watcher.getSubject());
      boolean finish=!handler.handleWatchEvent(this, doclock);
    doclock=null; // TODO: check that lock should really be released rather than dereferenced
    if (finish)
      haltWatch();
    else
      enableWatch();
    handlerCalled=false;
    return true;
  }

  /**
   * @return the handler
   */
  public WatcherCallBack getHandler() {
    return handler;
  }
  /**
   * @return the handlerCalled
   */
  public boolean isHandlerCalled() {
    return handlerCalled;
  }
  /**
   * 
   * @return true if watcher is enabled
   */
  public boolean isWatchEnabled() {
    return watchForChange;
  }
  /**
   * @param handler the handler to set
   */
  public void setHandler(WatcherCallBack handler) {
    this.handler = handler;
  }
  /**
   * @return the watcher
   */
  public FileWatcher getWatcher() {
    return watcher;
  }
}