Functional Term Size

FunctionalTermSize.scala

object Winch {
  // https://nodejs.org/api/tty.html
  case class Size(cols: Int, lines: Int)

  def build[F[_]: Async]: Resource[F, fs2.concurrent.Signal[F, Size]] = 
    Resource.eval(getCurrentSizeExternal).flatMap{
      Stream.repeatEval(singleEvent >> getCurrentSizeExternal)
        .holdResource(_)
    }

  def getCurrentSizeExternal[F[_]: Sync]: F[Size] = {
    Sync[F].delay{
      // Side-effect to call tput cols/lines
      val cols = TTY.consoleDim("cols")
      val lines = TTY.consoleDim("lines")
      Size(cols, lines)
    }
  }

  import sun.misc.{Signal, SignalHandler}

  def singleEvent[F[_]: Async]: F[Unit] = Async[F].async{ cb => 
    Async[F].delay{
      val terminalSizeChangedHandler: SignalHandler = {
        new SignalHandler {
          override def handle(sig: Signal): Unit = {
            cb(Right(()))
          }
        }
      }
      Signal.handle(new Signal("WINCH"), terminalSizeChangedHandler)
      None
    }
  }
}