class UnderflowException(msg: String) extends Exception(msg)

class Point(var x:Double = 0.0, var y:Double = 0.0) {
  override def toString= "[" + x + ", " + y + "]"
}

import java.awt.Color

class Pixel(xp:Double=0.0, yp:Double=0.0,
    var color:Color= Color.BLACK) extends Point(xp, yp) {

  override def toString = super.toString+ " " + color
}


class Queue[+T] private(private val queue: (List[T], List[T])) {

  def enqueue[S >: T](element: S): Queue[S] = {
    val (firstList, secondList) = queue
    normalize(firstList, element :: secondList)
  }

  private def normalize[S >: T](list1: List[S], list2: List[S]) =
    (list1, list2) match {
      case (Nil, secondList) => new Queue[S]((secondList.reverse, Nil))
      case normalQueue => new Queue(normalQueue)
    }

  def dequeue: Queue[T] =
    queue match {
      case (_ :: tl, secondList) => normalize(tl, secondList)
      case _ => Queue.empty
    }

  def first: T =
    queue._1 match {
      case (hd :: _) => hd
      case _ => throw new UnderflowException("first")
    }

  def isEmpty: Boolean =
    queue._1 == Nil

  override def toString = "{ " + queue._1.toString + " | " + queue._2.toString + "}"

}

object Queue {
  def apply[T](xs: T*) = new Queue[T](xs.toList, Nil)

  def empty[T] = new Queue[T](Nil, Nil)
}




  val qP = Queue(new Point(1,1),new Point(3,3),new Point(5,5))
  val qPx = Queue.empty
  val qPx1 = Queue.empty

  qP.enqueue(new Point(7,7))
  qPx.enqueue(new Pixel(2,2,Color.RED))

  val qPx1 = qOfPixels.dequeue

  val qP1:Queue[Point] = Queue(new Pixel(1,1))
  qP1.first.asInstanceOf[Pixel]

  qP.dequeue

  qPx.first
  qP.first