package uk.ac.vamsas.client.simpleclient;

import java.util.Iterator;
import java.util.Vector;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 * Watches a bunch of VamsasFile states, calling 
 * the associated event handler when anything changes.
 * @author JimP
 *
 */
public class VamsasFileWatcherThread extends Thread {
  private Log log = LogFactory.getLog(VamsasFileWatcherThread.class);  
  /* (non-Javadoc)
   * @see java.lang.Thread#run()
   */
  EventGeneratorThread client=null;
  private Vector elements=null;
  public VamsasFileWatcherThread(EventGeneratorThread client) {
    this.client = client;
    elements=new Vector();
  }
  public void addElement(WatcherElement welement) {
    elements.addElement(welement);
  }
  public void removeElemenet(WatcherElement welement) {
    elements.removeElement(welement);
  }
  public void clearElements() {
    elements.clear();
  }
  /**
   * true if the thread is running
   */
  boolean running=false;
  /**
   * true if the watcher loop is in progress
   */
  boolean watching=false;
  public void haltWatchers() {
    if (!watching)
      return;
    watching=false;
    // wait arount for WATCH_SLEEP milliseconds before returning
    // in the hope that the watcher loop has stopped
    try {
      long time = System.currentTimeMillis()+WATCH_SLEEP;
      interrupt();
      while (running && time>System.currentTimeMillis()) {
        Thread.sleep(1);
      }
    } catch (Exception e) {};
    if (running)
      log.warn("haltWatchers returning whilst thread is still running.");
  }
  
  /**
   * time between checks for changes of state on the file
   */
  public int WATCH_SLEEP=30; 
  /**
   * check each watcher in sequence, monitoring any events generated.
   * Then wait WATCH_SLEEP milliseconds before checking all again (if there were no events)
   */
  public void run() {
    running=true;
    watching=true;
    log.debug("Starting WatcherThread poll loop");
    while (watching) {
      boolean wait=true;
      Iterator watchers=elements.iterator();
      while (watching && watchers.hasNext()) {
        WatcherElement watch = (WatcherElement) watchers.next();
        if (watch.doWatch()) {
          wait=false;
          log.debug("Event generated for watcher on "+watch.getWatcher().getSubject());
        }
      }
      if (watching && wait) {
        try {
          Thread.sleep(WATCH_SLEEP);
        }
        catch (InterruptedException e) {};
      }
    }
    log.debug("Finishing WatcherThread poll loop");
    running=false;
  }
}