TryOps.scala

object TryOps {
  import scala.util.{Failure, Try, Success}
  import scala.annotation.tailrec

  /*can be used as :
   (Try {
   HTTP.get(".....")
   }).retryGet(3)
    */

  @tailrec
  def lowRetry[T](f:() => Try[T])(n:Int)(ref:Option[Int] = None, maxAttempts:Option[Int] = None):Try[T]  = {
    require(n > 0)
    if(n == 1){
      maxAttempts match {
        case Some(nMax) => f().recoverWith({case e => Failure(new Exception(s"max retry $nMax",e))})
        case _ => f()
      }
    } else {
      val t = f()
      val nref = System.identityHashCode(t)
      if(ref.contains(nref)) {
         t.recoverWith({case e => Failure(new Exception("can't retry eager try", e))})
      } else {
        t match {
          case _:Success[T] => t
          case Failure(e) => lowRetry(f)(n - 1)(Some(nref), maxAttempts orElse Some(n)) 
        }
      }
    }
  }

  implicit class TryOps[T](t: => Try[T]) {
    def retry(n: Int): Try[T] = lowRetry(() => t)(n)()
  }

  def retry[T](t: => Try[T])(n: Int): Try[T] = TryOps(t).retry(n)

  def main(args: Array[String]): Unit = {
    var i = 0
    val v = Try {
      i = i + 1
      if (i == 1) {
        println("first try")
        throw new Exception("0")
      } else {
        println("second try")
        2
      }
    }.retry(3)

    assert(v == Try(2))
    assert(i == 2)
  }
}