Example.scala

import zio.{DefaultRuntime, Task, ZIO}

import scala.io.StdIn

object Example extends App {

  object Console {
    trait Service {
      def getStrLn(): Task[String]
      def putStrLn(s: String): Task[Unit]
    }
  }
  trait Console {
    def console: Console.Service
  }

  object cs {

    def getStrLn(): ZIO[Console, Throwable, String] =
      ZIO.accessM(_.console.getStrLn())

    def putStrLn(s: String): ZIO[Console, Throwable, Unit] =
      ZIO.accessM(_.console.putStrLn(s))
  }

  trait ConsoleLive extends Console {
    def console: Console.Service =
      new Console.Service {
        def getStrLn(): Task[String] = ZIO.effect(StdIn.readLine())
        def putStrLn(s: String): Task[Unit] = ZIO.effectTotal(println(s))
      }
  }
  object ConsoleLive extends ConsoleLive

  class TestService extends Console.Service {
    private var stdin: List[String] = List()
    private var stdout: List[String] = List()

    def setStdIn(s: List[String]): Task[Unit] =
      ZIO.effectTotal { stdin = s }

    def getStdOut: Task[List[String]] =
      ZIO.effect(stdout)

    def getStrLn(): Task[String] =
      for {
        res <- Task(stdin)
        x :: xs = res
        _ <- ZIO.effectTotal { stdin = xs }
      } yield x

    def putStrLn(s: String): Task[Unit] =
      ZIO.effectTotal { stdout = s :: stdout }
  }
  trait TestConsole extends Console {
    val console: TestService = new TestService
  }
  object TestConsole extends TestConsole

  def code: ZIO[Console, Throwable, Unit] =
    for {
      name <- cs.getStrLn()
      _ <- cs.putStrLn(name)
    } yield ()

  def code1: ZIO[Any, Throwable, Unit] =
    code.provide(ConsoleLive)

  def code2: ZIO[Any, Throwable, Unit] =
    code.provide(TestConsole)

  def run(args: List[String]) = {
    val runtime = new DefaultRuntime {}
    runtime.unsafeRun(code1)
  }
}