day1.scala

object Day1 extends Challenge {
  override def runFirst(): Unit = {
    val startPosition = Position.start
    val endPosition = loadInput().foldLeft(startPosition) {
      case (p, ("R", l)) =>
        p.turnRight().walk(l.toLong)
      case (p, ("L", l)) =>
        p.turnLeft().walk(l.toLong)
    }

    println(startPosition.distanceTo(endPosition))
  }

  override def runSecond(): Unit = {
    val startPosition = Position.start
    val positions = loadInput().foldLeft(Seq(startPosition)) {
      case (p, ("R", l)) =>
        p.init ++ 1.to(l.toInt).scanLeft(p.last.turnRight())((a, _) => a.walk(1))
      case (p, ("L", l)) =>
        p.init ++ 1.to(l.toInt).scanLeft(p.last.turnLeft())((a, _) => a.walk(1))
    }

    def findFirstDuplicate(list: List[Position]): Option[Position] = list match {
      case head :: tail if tail.exists(p => p.x == head.x && p.y == head.y) =>
        Some(head)
      case head :: tail =>
        findFirstDuplicate(tail)
    }

    findFirstDuplicate(positions.toList).foreach(d => println(d.distanceTo(startPosition)))
  }

  def loadInput(): Array[(String, String)] =
    loadFile("day1.txt").mkString.split(',').map(_.trim.splitAt(1))

  object Direction extends Enumeration {
    type Direction = Value
    val North = Value(0)
    val East = Value(1)
    val South = Value(2)
    val West = Value(3)
  }

  case class Position(direction: Direction, x: Long, y: Long) {
    def distanceTo(position: Position): Long = (position.x - x).abs + (position.y - y).abs

    def turnLeft(): Position = this.copy(Direction((((direction.id - 1) % 4) + 4) % 4))

    def turnRight(): Position = this.copy(Direction((direction.id + 1) % 4))

    def walk(steps: Long): Position =
      this.direction match {
        case Direction.North => this.copy(y = y + steps)
        case Direction.East => this.copy(x = x + steps)
        case Direction.South => this.copy(y = y - steps)
        case Direction.West => this.copy(x = x - steps)
      }
  }

  case object Position {
    def start: Position = Position(Direction.North, 0, 0)
  }
}