import cats.implicits._
import cats.effect.IO
import doobie._
import doobie.implicits._
import fs2.Stream

object Main extends App {
  case class RedisClient()

  val xa = Transactor.fromDriverManager[IO](
    "org.postgresql.Driver", "jdbc:postgresql:world", "postgres", ""
  )

  type Query[A] = (Int, Int) => ConnectionIO[A]
  type Consume[A] = (RedisClient, A) => Unit

  def offsets(lim: Int): Stream[IO, Int] =
    Stream.iterate(0)(_ + lim)

  def withClient[A](f: RedisClient => A): A = ???

  def find[A](limit: Int, offset: Int): ConnectionIO[List[Int]] = ???

  def store(rc: RedisClient, rows: List[Int]): Unit = ???

  def queryWithLimit[A](q: Query[A], limit: Int, sink: Consume[A]): IO[Unit] = {
    val s = for {
      off <- offsets(limit)
      rows <- Stream.eval(find(off, limit).transact(xa))
      _ <- Stream.eval(IO(sink()))
    } yield rows.size

    s.takeThrough(_ == limit).compile.drain
  }

  def run(rc: RedisClient, limit: Int): IO[Unit] = {
    val s = for {
      off <- offsets(limit)
      rows <- Stream.eval(find(off, limit).transact(xa))
      _ <- Stream.eval(IO(store(rc, rows)))
    } yield rows.size

    s.takeThrough(_ == limit).compile.drain
  }

  val main: IO[Unit] = withClient { rc => run(rc, 100) }
}