import cats.effect._
import cats.effect.concurrent.Semaphore
import cats.effect.implicits._
import cats.implicits._
import scala.concurrent.duration._

object SharedState extends IOApp {

  // Not present in the book, added for compilability
  def putStrLn(str: String): IO[Unit] = IO(println(str))

  def someExpensiveTask: IO[Unit] = {
    IO.sleep(1.second) >> putStrLn("expensive task") >> someExpensiveTask
  }

  def p1(s: Semaphore[IO]): IO[Unit] = s.withPermit(someExpensiveTask) >> p1(s)

  def p2(s: Semaphore[IO]): IO[Unit] = s.withPermit(someExpensiveTask) >> p2(s)

  override def run(args: List[String]): IO[ExitCode] =
    Semaphore[IO](1).flatMap { sem =>
      p1(sem).start.void *> p2(sem).start.void
    } *>
      IO.never.as(ExitCode.Success)
}

def someExpensiveTask: IO[Unit] = {
    IO.sleep(1.second) >> putStrLn("expensive task")
  }

  def someTask(x:Int): IO[Unit] = {
    IO.sleep(1.second) >> putStrLn("SomeTask called by " ++ x.toString)
  }

  def p1(s:Semaphore[IO]):IO[Unit] = s.withPermit(someTask(1)) >> p1(s)

  def p2(s:Semaphore[IO]):IO[Unit] = s.withPermit(someTask(2)) >> p2(s)

  override def run(args: List[String]): IO[ExitCode] =
    Semaphore[IO](1).flatMap{s => p1(s).start *> p2(s).start} *>
      IO.never.as(ExitCode.Success)

object RunMeResource extends IOApp {
  override def run(args: List[String]): IO[ExitCode] =
    StreamResource
      .make[IO]
      .use(bg => bg.schedule(IO(println("happy")), 3.second)) *>
      IO.sleep(5.seconds) *> // (A)
      IO.pure(ExitCode.Success)
}