DelayedFuture.scala

object DelayedFuture {

  import java.util.{Timer, TimerTask}
  import java.util.Date
  import scala.concurrent._
  import scala.concurrent.duration.FiniteDuration

  private val timer = new Timer(true)

  private def makeTask[T](
      body: => Future[T]
  )(schedule: TimerTask => Unit)(implicit ctx: ExecutionContext): Future[T] = {
    val promise = Promise[T]()
    schedule(
      new TimerTask {
        def run(): Unit = {
          // IMPORTANT: The timer task just starts the execution on the passed
          // ExecutionContext and is thus almost instantaneous (making it
          // practical to use a single  Timer - hence a single background thread).
          ctx.execute(() => { promise.completeWith(body) }
          )
        }
      }
    )
    promise.future
  }

  def apply[T](delay: FiniteDuration)(body: => Future[T])(implicit ctx: ExecutionContext): Future[T] = {
    makeTask(body)(timer.schedule(_, delay.toMillis))
  }
}