import scala.util.Random
import scala.concurrent.duration._

import cats.effect.{ExitCode, IO, IOApp}
import cats.implicits._
import fs2.Stream
import scala.concurrent.ExecutionContext.Implicits.global
import java.time.{Clock, ZoneOffset}

import fs2.concurrent.SignallingRef

object InterruptipleQueue extends IOApp {
  override def run(args: List[String]): IO[ExitCode] = {
    val clock = Clock.systemUTC()

    def interrupter(signallingRef: SignallingRef[IO, Boolean]): Stream[IO, Unit] = {
      for {
        _ <- Stream.fixedDelay(1.seconds) // check every 1 second
        _ <- Stream.eval {
          val t  = clock.instant().atOffset(ZoneOffset.UTC)
          val on = t.getSecond <= 30  // the on/off logic (e.g. a light switch)
          signallingRef.access flatMap {
            case (current, set) =>
              //  need update?
              if (on != current) {
                if (on) println(s"Seconds of $t <= 30: turning OFF.")
                else    println(s"Seconds of $t > 30: turning ON.")
                set(on)
              } else IO.unit
          }
        }
      } yield ()
    }

    def printer(signallingRef: SignallingRef[IO, Boolean]): Stream[IO, Int] = {
      Stream
        .iterateEval(0)(i => IO(i + 1))
        .metered(100 millis)
        .pauseWhen(signallingRef)
    }

    (for {
      signal <- Stream.eval(SignallingRef[IO, Boolean](false))
      ints   <- printer(signal).concurrently(interrupter(signal))
    } yield ints)
      .evalMap(i => IO(println(s"Got $i")))
      .compile
      .drain
      .as(ExitCode.Success)
  }

}