A script to sort a list of elements according to the user input

Tempo.scala

/**
  * @author Louis Vialar
  */

import java.io.File

import scala.collection.immutable.Stack
import scala.io.{Source, StdIn}

object Tempo {
  def prompt(elem: String, head: String): Int = {
    print(elem + " vs " + head + " => (1) ou (2) [0 to go back] ? ")
    try {
      val selected = StdIn.readInt()
      if (selected >= 0 && selected <= 2) return selected
    } catch {
      case e: NumberFormatException => println("Pas un nombre :x")
    }

    prompt(elem, head)
  }

  def insertionSort(toSort: List[String], sorted: List[String], states: List[(List[String], List[String])]): List[String] = {
    def insertElement(elem: String, sorted: List[String]): List[String] = {
      if (sorted.isEmpty) return List(elem)

      val head = sorted.head
      val selected = prompt(elem, head)

      if (selected == 1) elem :: sorted
      else if (selected == 0) null
      else head :: insertElement(elem, sorted.tail)
    }

    if (toSort.isEmpty) sorted
    else {
      val sort = toSort.head
      val nSorted = insertElement(sort, sorted)

      if (nSorted == null) {
        if (states.isEmpty || states.tail.isEmpty) {
          println("Erreur fatale : liste d'états vide.")
          List()
        } else {
          val state = states.tail.head
          insertionSort(state._1, state._2, states.tail)
        }
      } else insertionSort(toSort.tail, nSorted, (toSort.tail, nSorted) :: states)
    }
  }

  def main(args: Array[String]): Unit = {
    print("Chemin du fichier : ")
    val path = StdIn.readLine()
    val file = new File(path)

    if (!file.exists()) {
      println(s"Le fichier ${file.getAbsolutePath} n'existe pas")
    }

    println("Lecture...")
    val data = Source.fromFile(file).getLines().toList
    val sorted = insertionSort(data, List(), (data, List()) :: Nil)
    println("Terminé !")
    println("------------------------------")
    val numbers = 1 to data.size
    numbers.zip(sorted).foreach({
      case (num, v) => println(s"#$num : $v")
    })
  }

}