UptimeApp.scala

package org.teckhooi

import cats.effect.{ExitCode, IO, IOApp}
import cats.effect.IO.ioParallel // requires for UptimeService[IO]
import cats.{Id, Monad, Parallel, Show}
import cats.syntax.parallel._
import cats.syntax.functor._
import cats.syntax.traverse._ // requires for traverse
import cats.syntax.show._
import cats.syntax.flatMap._ // requires for UptimeService[Id]
import scala.concurrent.duration.{Duration, SECONDS}
import scala.concurrent.{Await, Future}

object UptimeApp extends IOApp {
  trait UptimeClient[F[_]] {
    def getUptime(hostname: String): F[Int]
  }

  class UptimeService[F[_]: Monad: Parallel](implicit client: UptimeClient[F]) {
    def getTotalUptime(hostnames: List[String]): F[Int] =
//      hostnames.parTraverse(client.getUptime).map(_.sum)  // takes 1s to complete
      hostnames.traverse(client.getUptime).map(_.sum) // takes 2s to complete
  }

  val hosts: Map[String, Int] = Map("host1" -> 10, "host2" -> 8)

  import concurrent.ExecutionContext.Implicits.global

  implicit object FutureClient extends UptimeClient[Future] {
    override def getUptime(hostname: String): Future[Int] = {
      Thread.sleep(1000)
      Future(hosts.getOrElse(hostname, 0))
    }
  }

  implicit object IOClient extends UptimeClient[IO] {
    override def getUptime(hostname: String): IO[Int] = {
      IO.sleep(Duration(1, SECONDS)) *> IO.pure(hosts.getOrElse(hostname, 0))
    }
  }

  implicit object IdClient extends UptimeClient[Id] {
    override def getUptime(hostname: String): Int = hosts.getOrElse(hostname, 0)
  }

  implicit def showFuture[A: Show]: Show[Future[A]] =
    (t: Future[A]) => Await.result(t, Duration(1, SECONDS)).show

  override def run(args: List[String]): IO[ExitCode] = {
    for {
      startMillis <- IO(System.currentTimeMillis())
      service = new UptimeService[IO]
      result <- service.getTotalUptime(List("host1", "host2"))
      _      <- IO(println(s"Result: $result"))
      _      <- IO(println(s"Time taken: ${System.currentTimeMillis() - startMillis}ms"))
    } yield ExitCode.Success
  }
}