almost-good-api.scala

import scala.concurrent.ExecutionContext.Implicits.global
import scala.concurrent.{ExecutionContext, Future}

trait Request

trait Response

trait CacheService {
  def isDuplicateRequest(request: Request)(implicit ec: ExecutionContext): Future[Option[Request]]

  def setCacheForDeduplication(dedupedReq: Option[Request])(implicit ec: ExecutionContext): Future[Boolean]
}

trait Processor {
  def process(request: Option[Request])(implicit ec: ExecutionContext): Future[Response]
}

class API(cacheService: CacheService, processor: Processor) {

  def process(request: Request): Future[Response] = {
    for {
      dedupedRequest <- cacheService.isDuplicateRequest(request)
      response <- processor.process(dedupedRequest)
      _ <- cacheService.setCacheForDeduplication(dedupedRequest) // what's wrong here?
    } yield response
  }
}