Monadic-ScalaFX-Demo/src/test/scala/ObservableTest.scala

import org.scalatest.funsuite.AnyFunSuite
import monix.catnap.ConcurrentQueue
import monix.eval.Task
import monix.reactive.Observable
import scala.concurrent.duration._

class ObservableTest extends AnyFunSuite {
  import monix.execution.Scheduler.Implicits.global
  test("observable state machine") {
    (for {
      _ <- Task.unit
      sm <- MonixStateMachine()
      _ <-
        Task
          .parSequence(
            List(
              sm.source
                .doOnNext(item => Task(println(s"Task 1: Got $item")))
                .completedL,
              sm.source
                .doOnNext(item => Task(println(s"Task 2: Got $item")))
                .completedL,
              sm.tell(MonixStateMachine.Start) >>
                Observable
                  // .interval(1.second)
                  .interval(500.millis)
                  .doOnNext(_ => sm.tell(MonixStateMachine.Incr))
                  .takeUntil(Observable.unit.delayExecution(5.seconds))
                  .completedL >>
                sm.tell(MonixStateMachine.Stop) >>
                sm.tell(MonixStateMachine.Incr)
            )
          )
          .void
          .start
          .bracket(_ => Task.sleep(8.seconds))(_.cancel)
    } yield ()).runSyncUnsafe(10.seconds)
  }
}

class MonixStateMachine(
    queue: ConcurrentQueue[Task, MonixStateMachine.Command],
    val source: Observable[(MonixStateMachine.State, MonixStateMachine.Data)]
) {
  import MonixStateMachine._

  def tell(item: Command) = queue.offer(item)

}
object MonixStateMachine {

  sealed trait State
  case object Idle extends State
  case object Active extends State

  sealed trait Command
  case object Incr extends Command
  case object Start extends Command
  case object Stop extends Command

  case class Data(num: Int)

  private def source(queue: ConcurrentQueue[Task, Command]) =
    Task.deferAction(implicit s =>
      Task(
        Observable
          .repeatEvalF(queue.poll)
          .scan((Idle: State, Data(0))) {
            case ((state, data), command) =>
              state match {
                case Idle =>
                  println("Entered idle")
                  command match {
                    case Incr =>
                      println("Not active ")
                      (Idle, data)
                    case Start => (Active, data)
                    case Stop =>
                      println("Already stopped")
                      (Idle, data)

                  }
                case Active =>
                  println("Entered Active")
                  command match {
                    case Incr => (Active, data.copy(num = data.num + 1))
                    case Start =>
                      println("Already started")
                      (Active, data)
                    case Stop => (Idle, data)
                  }
              }
          }
          .publish
          .refCount
      )
    )

  def apply() =
    for {
      queue <- ConcurrentQueue.bounded[Task, Command](10)
      source <- source(queue)
    } yield new MonixStateMachine(queue, source)
}