package uk.ac.vamsas.client.simpleclient;


/**
 * Element of the VamsasFileWatcherThread event generator chain.
 * Keep a reference to this element before adding it to the chain 
 * in order to control the generation of events with halt and enable.
 * 
 * doWatch will do nothing if the element is not enabled.
 * 
 */
public class SessionFileWatcherElement extends WatcherElement {
  SessionFile watched=null;
  /**
   * create a new, enabled watch element
   * @param watcher file being watched
   * @param handler handler to call on state change
   */
  public SessionFileWatcherElement(SessionFile watcher, WatcherCallBack handler) {
    this(watcher, handler, true);
  }
  protected void initWatch() {
    if (watched==null)
      return;
    if (watcher==null || !watcher.getSubject().equals(watched.sessionFile)) 
      watcher=new FileWatcher(watched.sessionFile);
    else
      watcher.setState();
  }
  protected void endWatch() {
    // leaves watcher in state its in.
  }
  /**
   * new watcher with flag to initially skip watching this sessionfile
   * @param watcher
   * @param handler
   * @param enableWatching
   */
  public SessionFileWatcherElement(SessionFile watcher, WatcherCallBack handler, boolean enableWatching) {
    super(handler);
    this.watched = watcher;
    if (enableWatching)
      enableWatch();
    else
      haltWatch();
  }
  /**
   * @return the watched
   */
  public SessionFile getWatched() {
    return watched;
  }
  protected String getSubject() {
    return watched.sessionFile.toString();
  }
}