ratelimit.scala

class ApiService[T](limit: Long, timeFrame: FiniteDuration) {
  // other code ...

  private def makeRequest(): Unit = {
    val req = requestQueue.pollFirst()
    if (req == null) {
      return
    }

    requestCount += 1
    val result = req.f()

    // re-queue at the head of the queue on failure and
    // attempt to make another request
    def retry(): Unit = this.synchronized {
      requestQueue.offerFirst(req)
      tryRequest()
    }

    result.onComplete {
      case Failure(t: Throwable) =>
        if (req.limitDetector(Left(t))) {
          retry()
        } else {
          req.p.complete(Failure(t))
        }

      case Success(r) =>
        if (req.limitDetector(Right(r))) {
          retry()
        } else {
          req.p.complete(Success(r))
          tryRequest()
        }
    }
  }
  
}