Scala Error Handling

0_Routes.scala

val route =
  path("order") {
    post {
      entity(as[OrderRequest]) { orderRequest =>
        onComplete(PurchaseService.createPurchase(orderRequest)) {
          case Success(result) =>
            complete(StatusCodes.Created, result)
          case Failure(exception) =>
            system.log.error(exception, "Unexpected error")
            complete(StatusCodes.InternalServerError,
                     HttpEntity(ContentTypes.`application/json`,
                                "{\"error\": true}"))
        }
      }
    }
  }

1_PurchaseService.scala

object PurchaseService {

  final case class Order(orderId: String)

  def createPurchase(orderRequest: OrderRequest)(
      implicit ec: ExecutionContext): Future[Order] = {
    PaymentClient.chargeCard(orderRequest.cardNumber).map { _ =>
      Order(orderId = UUID.randomUUID().toString)
    }
  }
}

2_PaymentClient.scala

object PaymentClient {

  final case class Charge(chargeId: UUID)

  sealed trait PaymentException extends Throwable
  final class CardException(val declineCode: String) extends PaymentException
  final class NotEnoughFundException extends PaymentException
  final class UnknownPaymentException extends PaymentException
  final class RateLimitException extends PaymentException
  final class InvalidRequestException extends PaymentException
  final class AuthenticationException extends PaymentException
  final class APIConnectionException extends PaymentException

  def chargeCard(cardNumber: String)(
      implicit ec: ExecutionContext): Future[Charge] = {
    // Fake an API call
    Future {
      if (cardNumber == "valid") {
        Charge(UUID.randomUUID())
      } else if (cardNumber.startsWith("card_error")) {
        val declineCode = cardNumber.split("_").toList.drop(2).mkString("_")
        throw new CardException(declineCode)
      } else if (cardNumber == "rate_limit_error") {
        throw new RateLimitException()
      } else if (cardNumber == "invalid_request_error") {
        throw new InvalidRequestException()
      } else if (cardNumber == "authentication_error") {
        throw new AuthenticationException()
      } else if (cardNumber == "api_connection_error") {
        throw new APIConnectionException()
      } else {
        throw new UnknownPaymentException()
      }
    }
  }
}