RetryOps.scala

import uk.ac.wellcome.storage.RetryableError

import scala.util.Random
import scala.annotation.tailrec

object RetryOps {
  implicit class Retry[In, Out, Error](f: In => Either[Error, Out]) {

    def retry(maxAttempts: Int = 1): In => Either[Error, Out] =
      (in: In) => retryInternal(maxAttempts)(in)

    @tailrec
    private def retryInternal(remainingAttempts: Int)(in: In): Either[Error, Out] =
      f(in) match {
        case Right(out) => Right(out)

        // We can't use `Left(err: RetryableError)` because
        // the compiler needs to know that Left(err) in
        // the if branch is an instance of Error.
        //
        // Even though we know that err is both an Error and
        // a RetryableError (because it comes from f(in)),
        // the compiler can't see that.
        case Left(err) if err.isInstanceOf[RetryableError] =>
          if (remainingAttempts == 1) {
            Left(err)
          } else {
            retryInternal(remainingAttempts - 1)(in)
          }

        case Left(err) => Left(err)
      }
  }
}