package io.github.timwspence.cats.stm
import cats.effect.{ExitCode, IO, IOApp}
//import io.github.timwspence.cats.stm.{TVar, STM}
import scala.concurrent.duration._
object Main extends IOApp {
override def run(args: List[String]): IO[ExitCode] =
for {
accountForTim <- TVar.of[Long](100).commit[IO]
accountForSteve <- TVar.of[Long](0).commit[IO]
_ <- printBalances(accountForTim, accountForSteve)
_ <- giveTimMoreMoney(accountForTim).start
_ <- transfer(accountForTim, accountForSteve)
_ <- printBalances(accountForTim, accountForSteve)
} yield ExitCode.Success
private def transfer(accountForTim: TVar[Long], accountForSteve: TVar[Long]): IO[Unit] =
STM.atomically[IO] {
for {
balance <- accountForTim.get
_ <- STM.check(balance > 100)
_ <- accountForTim.modify(_ - 100)
_ <- accountForSteve.modify(_ + 100)
} yield ()
}
private def giveTimMoreMoney(accountForTim: TVar[Long]): IO[Unit] =
for {
_ <- IO.sleep(5000.millis)
_ <- STM.atomically[IO](accountForTim.modify(_ + 1))
} yield ()
private def printBalances(accountForTim: TVar[Long], accountForSteve: TVar[Long]): IO[Unit] =
for {
(amountForTim, amountForSteve) <- STM.atomically[IO](for {
t <- accountForTim.get
s <- accountForSteve.get
} yield (t, s))
_ <- IO(println(s"Tim: $amountForTim"))
_ <- IO(println(s"Steve: $amountForSteve"))
} yield ()
}
