Schedule.scala

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

object Schedule {

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

  def apply[T](date: Date)(body: => Future[T])(implicit ctx: ExecutionContext): Future[T] =
    makeTask(body)(timer.schedule(_, date))

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

  private val timer = new Timer(true)

  private def makeTask[T](
    body: => Future[T]
  )(schedule: TimerTask => Unit)(implicit ctx: ExecutionContext): Future[T] = {
    val prom = Promise[T]()
    schedule(
      new TimerTask {
        def run() {
          // 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).
          body.transform(
            { result: T =>
              prom.complete(Success(result))
              result
            },
            { error: Throwable =>
              prom.complete(Failure(error))
              error
            }
          )
        }
      }
    )
    prom.future
  }
}