Format a duration as HH:MM:SS

formatTime.coffee

divmod = (num1, num2) ->
  [num1 / num2, num1 % num2]

formatInterval = (start) ->
  total = parseInt((Date.now() - start) / 1000, 10)
  [hours, rest] = divmod(total, 60 * 60)
  [minutes, seconds] = divmod(rest, 60)
  sprintTime(hours, minutes, seconds)

sprintTime = ->
  parts = for arg in arguments
    num = parseInt(arg, 10)
    if num < 10
      '0' + num
    else
      num
  parts.join(":")