!7

module UserActivityDetector > DynBigNumber {
  static long lastActivity;
  static transient persistedLastActivity;
  
  start {
    dm_startKeyLogger();
    persistedLastActivity = lastActivity;
    dm_vmBus_onMessage('keyDown, r activity);
    doEvery(5*60.0, r saveIfChanged);
  }
  
  void saveIfChanged enter {
    if (lastActivity != persistedLastActivity) {
      persistedLastActivity = lastActivity;
      change();
    }
  }
  
  // API
  
  void activity enter {
    lastActivity = now();
  }
  
  double secondsSinceLastActivity() {
    ret lastActivity == 0 ? infinity() : toSeconds(now()-lastActivity);
  }
}