[Prototype-core] PeriodicalExecuter with pause/restart w/o losing track of timer

[disccomp]

I needed pause/restart for one of my projects. Someone wrote an
extension once for this purpose, but the link was dead. And thanks for
all your hard work! -Mark

var PeriodicalExecuter = Class.create({
  initialize: function(callback, frequency) {
    this.callback = callback;
    this.frequency = frequency;
    this.currentlyExecuting = false;
    this.lastExec = this.now();
    this.paused = false;
    this.pausedAt = 0;
    this.accumTimePaused = 0;
    this.registerCallback();
  },

  registerCallback: function() {
    this.timer = setInterval(this.onTimerEvent.bind(this),
this.frequency * 1000);
  },

  execute: function() {
    this.callback(this);
  },

  pause: function(){
    if(this.timerRescheduler>0){clearTimeout(this.timerRescheduler)}
    if (this.paused) return;
    this.stop();
    this.paused = true;
    this.pausedAt = this.now();
    return true;
  },

  timeLeft: function(){
    if(this.paused){
      return this.frequency - (this.pausedAt - this.accumTimePaused -
this.lastExec);
    }else if(this.timer==null){
      return null;
    }else{
      return this.frequency - (this.now() - this.accumTimePaused -
this.lastExec);
    }
  },

  restart: function(){
    if (this.paused){

      if(this.timerRescheduler>0){clearTimeout(this.timerRescheduler)}
      this.timerRescheduler =
setTimeout(this.reJobCallback.bind(this), this.timeLeft()*1000);
      this.accumTimePaused += this.now() - this.pausedAt;
    }else if(this.timer == null){
      this.registerCallback();
    }
    this.pausedAt = null;
    this.paused = false;
  },

  reJobCallback : function(){
    this.onTimerEvent();
    this.registerCallback();
    this.accumTimePaused = 0;
  },

  now: function(){ return new Date().getTime() / 1000;},

  stop: function() {
    if (!this.timer) return;
    clearInterval(this.timer);
    this.timer = null;
  },

  onTimerEvent: function() {
    if (!this.currentlyExecuting) {
      try {
        this.currentlyExecuting = true;
        this.execute();
      } finally {
        this.currentlyExecuting = false;
        this.lastExec = this.now();
      }
    }
  }
});
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