SettleDownTimer.swift

//
//  SettledownTimer.swift
//
//
//  Created by Alexis Gallagher
//  known-good: Swift 2.2, Xcode 7.3.1
//

import Foundation

// not started : self.timer  = nil
// running     : self.timer != nil, isValid=true
// finished    : self.timer != nil, isValid=false


/*
 Use the SettleDownTimer in order to trigger FINAL_EVENT once only after 
 REPEATING_EVENT fails to happen within DURATION.
 
 To use, configure the block to perform FINAL_EVENT.
 Whenever REPEATING_EVENT happens, call restart(). The block will be called only once, after
 `duration` from a call to `restart()`.
 
 This can be used as a truly horrible hack to cause an event to happen only once
 after layout completes. Not recommended!
 
 */
class SettleDownTimer : NSObject {
  private var timer:NSTimer?
  
  let duration:NSTimeInterval
  let block:()->()
  
  init(duration:NSTimeInterval, block:() -> ()) {
    self.duration = duration
    self.block = block
    super.init()
  }
  
  func restart() {
    if let timer = self.timer {
      // timer exists, so it is running or finished
      if timer.valid {
        // timer still running, so kill it and restart it
        timer.invalidate()
        self.timer = NSTimer.scheduledTimerWithTimeInterval(duration, target : self,  selector : #selector(SettleDownTimer.doBlock),  userInfo: nil, repeats : false)
      }
      else {
        // timer finished, so do nothing
      }
    }
    else {
      // timer does not exist, so start it
      self.timer = NSTimer.scheduledTimerWithTimeInterval(duration, target : self,  selector : #selector(SettleDownTimer.doBlock),  userInfo: nil, repeats : false)
    }
  }
  
  func doBlock() {
    self.block()
  }
  
  deinit {
    if let timer = self.timer {
      timer.invalidate()
    }
    self.timer = nil
  }
}