outwatch-test/src/main/scala/outwatchapp/util/reactive/DedicatedWorker.scala

package outwatchapp.util.reactive

import io.circe.Decoder
import io.circe.Encoder
import io.circe.Printer
import io.circe.parser._
import io.circe.syntax._
import monix.execution.Ack
import monix.execution.Cancelable
import monix.execution.cancelables.SingleAssignCancelable
import monix.reactive.Observable
import monix.reactive.Observer
import monix.reactive.OverflowStrategy
import org.scalajs.dom.raw.MessageEvent
import org.scalajs.dom.webworkers.DedicatedWorkerGlobalScope
import scala.concurrent.Future
import outwatchapp.util.reactive.Exceptions.WrongTypeException
// @js.native
// @JSGlobalScope
// object WorkerGlobal extends DedicatedWorkerGlobalScope

// class DedicatedWorkerImpl[T: Encoder: Decoder](wg: DedicatedWorkerGlobalScope) {
//   def run = Task.deferAction(implicit s =>
//     for {
//       _ <- Task.unit
//       sub <- Task(ConcurrentSubject.publish[T])
//     } yield ()
//   )
// }

object DedicatedWorker {
  def source[T: Decoder](wg: DedicatedWorkerGlobalScope) =
    Observable.create[T](OverflowStrategy.DropOld(50)) { sub =>
      val c = SingleAssignCancelable()
      def onmessageFn(event: MessageEvent): Unit = {
        event.data match {
          case s: String =>
            decode[T](s)
              .map { res =>
                if (sub.onNext(res) == Ack.Stop) c.cancel()
                res
              }
              .left
              .foreach(err =>
                sub.onError(
                  new Exception(s"Failed to decode $s. Error was $err")
                )
              )
          case other =>
            sub.onError(WrongTypeException(s"Received wrong type: $other"))
        }
      }
      wg.onmessage = onmessageFn _

      c := Cancelable(() => wg.onmessage = _ => ())
    }

  def sink[T: Encoder](wg: DedicatedWorkerGlobalScope) =
    new Observer[T] {
      val printer = Printer.noSpaces

      override def onNext(elem: T): Future[Ack] = {
        // wg.onoffline
        wg.postMessage(printer.print(elem.asJson))
        Ack.Continue
      }

      override def onError(ex: Throwable): Unit = ex.printStackTrace()

      override def onComplete(): Unit = println("Worker observer completed")

    }

  def apply[T: Encoder: Decoder](
      wg: DedicatedWorkerGlobalScope
  ): DedicatedWorker[T] = MonixProSubject.from(sink(wg), source(wg))
}