Timer.swift

import Foundation

class Timer {
  var timer = NSTimer()
  var handler: (Int) -> ()
  
  let duration: Int
  var elapsedTime: Int = 0
  
  init(duration: Int, handler: (Int) -> ()) {
    self.duration = duration
    self.handler = handler
  }
  
  func start() {
    self.timer = NSTimer.scheduledTimerWithTimeInterval(1.0, 
                               target: self, 
                             selector: Selector("tick"), 
                             userInfo: nil, 
                              repeats: true)
  }
  
  func stop() {
    timer.invalidate()
  }
  
  @objc func tick() {
    self.elapsedTime++

    self.handler(elapsedTime)

    if self.elapsedTime == self.duration {
      self.stop()
    }
  }
  
  deinit {
    self.timer.invalidate()
  }
}

//source: http://samuelmullen.com/2014/07/using-swifts-closures-with-nstimer/