//
// Scala implementation to test strings that match the expression a*bb* | aa*bc* | ef
// by Miguel Marques
//

object Main {

  val characters = Map('a' -> 0, 'b' -> 1, 'c' -> 2, 'e' -> 3, 'f' -> 4).withDefaultValue(5)

  val transitions = Array(
    Array(0, 0, 0, 0, 0, 0),
    Array(2, 3, 0, 6, 0, 0),
    Array(2, 4, 0, 0, 0, 0),
    Array(0, 3, 0, 0, 0, 0),
    Array(0, 3, 5, 0, 0, 0),
    Array(0, 0, 5, 0, 0, 0),
    Array(0, 0, 0, 0, 7, 0),
    Array(0, 0, 0, 0, 0, 0))

  val initialState = 1
  val finalStates = Set(3, 4, 5, 7)

  def eval(str: String): Boolean =
    finalStates contains (
      str.foldLeft(initialState) { (state, character) =>
        val charInt = characters(character)
        transitions(state)(charInt)
      })

  def main(args: Array[String]): Unit = {
    Stream continually {
      print("Enter a string to test (ctrl+z to exit): ")
      readLine
    } takeWhile (_ != null) foreach { line =>
      println(if (eval(line)) "accept" else "reject")
    }

    println("\nBye!!!")
  }

}