server.scala

import akka.actor.ActorSystem
import akka.http.scaladsl.Http
import akka.http.scaladsl.model.headers._
import akka.http.scaladsl.model._
import akka.http.scaladsl.util.FastFuture
import akka.stream.ActorMaterializer
import akka.util.ByteString
import scala.concurrent._

import kaleidoscope._

implicit val system       = ActorSystem()
implicit val executor     = system.dispatcher
implicit val materializer = ActorMaterializer()
implicit val http         = Http(system)

def JsonResponse(status: Int, json: String): HttpResponse = HttpResponse(
  status,
  entity = HttpEntity(ContentTypes.`application/json`, json)
)

def AsyncJsonResponse(status: Int, json: String): Future[HttpResponse] = 
  FastFuture.successful(JsonResponse(status, json))

def handler(request: HttpRequest): Future[HttpResponse] = {
  (request.method, request.header[`Content-Type`].map(_.contentType), request.uri.path.toString) match {
    case (HttpMethods.GET, _, r"/api/users/$userId@([^/]+)") => AsyncJsonResponse(200, s"""{"userId":"$userId"}""")
    case (HttpMethods.POST, Some(ContentTypes.`application/json`), r"/api/users") => {
      request.entity.dataBytes.runFold(ByteString.empty)(_ ++ _).map { body =>
        JsonResponse(201, body.utf8String)
      } 
    }
    case _ => AsyncJsonResponse(404, """{"error":"not found"}""")
  }
}

http.bindAndHandleAsync(handler, "0.0.0.0", 8888)