ratelimit.scala

import java.util.concurrent.{ScheduledThreadPoolExecutor, ScheduledFuture, TimeUnit}
import java.time.temporal.ChronoUnit

class ApiService[T](limit: Long, timeFrame: FiniteDuration) {
  // previous code ...
  
  private val timerPool = new ScheduledThreadPoolExecutor(1)
  @volatile private var recheckFut: Option[ScheduledFuture[_]] = None
  
  private def tryRequest(): Unit = this.synchronized {
    if (hasCapacity()) {
      if (recheckFut.isDefined) {
        recheckFut.map(_.cancel(true))
        recheckFut = None
      }
      makeRequest()
    } else if (recheckFut.isEmpty) {
      val timeRemaining = ChronoUnit.NANOS.between(LocalDateTime.now(), windowStopTime)
      recheckFut = Some(timerPool.schedule(
        (() => {
          recheckFut = None
          tryRequest()
        }): Runnable,
        timeRemaining,
        TimeUnit.NANOSECONDS
      ))
    }
  }
  
}