believer/track-duration

let parseSeconds = ms => ms /. 1000.

let parseHours = s => Js.Math.floor_float(s /. 3600.)

let parseMinutes = (s, h) => Js.Math.floor_float(s /. 60. -. 60. *. h)

let parseOutputSeconds = s =>
  Js.Math.floor_float(mod_float(s /. 60., 1.) *. 60.)

let addLeadingZero = x =>
  switch x {
  | x when x < 10. => `0${Js.Float.toString(x)}`
  | x => Js.Float.toString(x)
  }

let parse = ms => {
  let s = parseSeconds(ms)
  let h = parseHours(s)
  let m = parseMinutes(s, h)
  let outputSeconds = s->parseOutputSeconds->addLeadingZero

  switch h {
  | 0. => `${Js.Float.toString(m)}:${outputSeconds}`
  | h => `${Js.Float.toString(h)}:${addLeadingZero(m)}:${outputSeconds}`
  }
}