Helper to pretty print scala Duration

PrettyDuration.scala

import concurrent.duration._
import scala.annotation.tailrec

object PrettyDuration {
  val timeUnitList: List[TimeUnit] =
    DAYS ::
      HOURS ::
      MINUTES ::
      SECONDS ::
      MILLISECONDS ::
      MICROSECONDS ::
      NANOSECONDS ::
      Nil
  
  implicit class PrettyPrintableDuration(val duration: Duration) extends AnyVal {
    
    @tailrec
    private def prettyRec(acc: List[FiniteDuration], remUnits: List[TimeUnit], rem: FiniteDuration, isPast: Boolean): String = {
      remUnits match {
        case h :: t =>
          if (rem > Duration(1, h)) {
            val x = Duration(rem.toUnit(h).toLong, h)
            prettyRec(x :: acc, t, rem - x, isPast)
          } else {
            prettyRec(acc, t, rem, isPast)
          }
        case Nil =>
          acc.reverse.map(_.toString).mkString(" ") + (if (isPast) " ago" else "")
      }
    }

    def pretty: String = {
      duration match {
        case Duration.Zero => "now"
        case f: FiniteDuration if f < Duration.Zero => prettyRec(Nil, timeUnitList, f * -1, isPast = true)
        case f: FiniteDuration => prettyRec(Nil, timeUnitList, f, isPast = false)
        case Duration.Inf => "infinite"
        case Duration.MinusInf => "minus infinite"
        case _ => "undefined"
      }
    }
  }
}