function Timer(options) {
  options = options || {}
  this.onTick = options.onTick || function () {}
  this.onComplete = options.onComplete || function () {}

  this._duration = 0
  this._remaining = 0
  this._elapsed = 0
  this._startTime = 0
  this._pausedTime = 0
  this._intervalId = null
  this._running = false
  this._paused = false
  this._completed = false
}

Timer.prototype.start = function (duration) {
  this._duration = duration
  this._remaining = duration
  this._elapsed = 0
  this._completed = false
  this._running = true
  this._paused = false
  this._startTime = Date.now()
  this._tick()
  var self = this
  this._intervalId = setInterval(function () { self._tick() }, 1000)
}

Timer.prototype.pause = function () {
  if (!this._running || this._paused) return
  this._paused = true
  this._pausedTime = Date.now()
  clearInterval(this._intervalId)
  this._intervalId = null
}

Timer.prototype.resume = function () {
  if (!this._running || !this._paused) return
  this._startTime += Date.now() - this._pausedTime
  this._paused = false
  this._tick()
  var self = this
  this._intervalId = setInterval(function () { self._tick() }, 1000)
}

Timer.prototype.stop = function () {
  this._running = false
  this._paused = false
  clearInterval(this._intervalId)
  this._intervalId = null
  return this._elapsed
}

Timer.prototype._tick = function () {
  if (!this._running || this._paused) return
  this._elapsed = Math.floor((Date.now() - this._startTime) / 1000)
  this._remaining = Math.max(0, this._duration - this._elapsed)

  this.onTick({
    remaining: this._remaining,
    elapsed: this._elapsed,
    duration: this._duration
  })

  if (this._remaining <= 0 && !this._completed) {
    this._completed = true
    this.onComplete({ elapsed: this._elapsed, duration: this._duration })
  }
}

Object.defineProperty(Timer.prototype, 'isRunning', {
  get: function () { return this._running && !this._paused }
})

Object.defineProperty(Timer.prototype, 'isPaused', {
  get: function () { return this._paused }
})

Object.defineProperty(Timer.prototype, 'isCompleted', {
  get: function () { return this._completed }
})

Object.defineProperty(Timer.prototype, 'remaining', {
  get: function () { return this._remaining }
})

Object.defineProperty(Timer.prototype, 'elapsed', {
  get: function () { return this._elapsed }
})

module.exports = Timer