Adding user-defined rate-limit-error checking

ratelimit.scala

class ApiService[T](limit: Long, timeFrame: FiniteDuration) {
  // other code ...
  
  type LimitDetector = PartialFunction[Either[Throwable, T], Boolean]
  case class RequestQueueItem(f: () => Future[T],
                              p: Promise[T],
                              limitDetector: LimitDetector)
  
  private var limitDetection: LimitDetector = {
    case Left(_)  => true
    case Right(_) => false
  }
  
  def withDefaultLimitDetection(d: LimitDetector): ApiService[t] = {
    limitDetection = d
    this
  }

  def request(f: () => Future[T])
             (d: LimitDetector = limitDetection)
             : Future[T] = this.synchronized {
    val p = Promise[T]()
    requestQueue.offerLast(RequestQueueItem(f, p, d))
    tryRequest()
    p.future
  }
}