Bounded int queue POC

OhGodWhatHaveIDoneQueue.scala

package fsp

import scala.annotation.tailrec

class OhGodWhatHaveIDoneQueue[A](
  val min: Int,
  val _0: List[A],
  val _1: List[A],
  val _2: List[A],
  val _3: List[A]) {

  def enqueue(priority: Int, a: A): OhGodWhatHaveIDoneQueue[A] = {
    priority match {
      case 0 => new OhGodWhatHaveIDoneQueue(Math.min(min, 0), a :: _0, _1, _2, _3)
      case 1 => new OhGodWhatHaveIDoneQueue(Math.min(min, 1), _0, a :: _1, _2, _3)
      case 2 => new OhGodWhatHaveIDoneQueue(Math.min(min, 2), _0, _1, a :: _2, _3)
      case 3 => new OhGodWhatHaveIDoneQueue(Math.min(min, 3), _0, _1, _2, a :: _3)
      case x => this 
    }
  }

  def dequeue: Option[(A, OhGodWhatHaveIDoneQueue[A])] = min match { 
    case 0 => 
      val a      = _0.head
      val new0   = _0.tail
      val newMin = if (new0.isEmpty) {
        findMin(1)
      } else {
        0
      }

      Some((a, new OhGodWhatHaveIDoneQueue(newMin, new0, _1, _2, _3)))

    case 1 => 
      val a      = _1.head
      val new1   = _1.tail
      val newMin = if (new1.isEmpty) {
        findMin(2)
      } else {
        1
      }

      Some((a, new OhGodWhatHaveIDoneQueue(newMin, _0, new1, _2, _3)))

    case 2 =>
      val a      = _2.head
      val new2   = _2.tail
      val newMin = if (new2.isEmpty) {
        findMin(3)
      } else {
        2
      }

      Some((a, new OhGodWhatHaveIDoneQueue(newMin, _0, _1, new2, _3)))

    case 3 => 
      val a      = _3.head
      val new3   = _3.tail
      val newMin = if (new3.isEmpty) {
        findMin(3)
      } else {
        3
      }

      Some((a, new OhGodWhatHaveIDoneQueue(newMin, _0, _1, _2, new3)))

    case x => None
  }


  @tailrec
  private def findMin(i: Int): Int = i match {
    case 1 => if (_1.isEmpty) findMin(2) else 1
    case 2 => if (_2.isEmpty) findMin(3) else 2
    case 3 => if (_2.isEmpty) findMin(4) else 3
    case x => 4
  }
}

object OhGodWhatHaveIDoneQueue {
  def empty[A] = new OhGodWhatHaveIDoneQueue(4, List.empty[A], List.empty[A], List.empty[A], List.empty[A])
}