package scalevalapokalypsi.UI

import scala.concurrent.Future
import scala.concurrent.ExecutionContext.Implicits.global
import scala.io.StdIn.readLine
import scala.util.{Try, Success, Failure}

/** This class is for taking new lines from stdin when they are available.
  *  reading starts when either newLine or clear or startReading are called.
  */
class StdinLineReader:

	private var nextLine: Future[String] = Future.failed(Exception())

	/** Returns a new line of input as a Right when there are any.
	  * If there is no new line due to EOF, returns Left(true),
	  * if there is no new line due to some other error, returns Left(false)
	  */
	def newLine(): Either[Boolean, String] =
		this.nextLine.value match
			case Some(Success(s)) =>
				if s == null then
					Left(true)
				else
					this.startReading()
					Right(s)
			case Some(Failure(e)) =>
				this.startReading()
				Left(false)
			case None => Left(false)

	/** Discards the line that is currently being read and restarts reading */
	def startReading(): Unit =
		this.nextLine = Future(readLine())
		

end StdinLineReader