adventofcode1.scala

object Xmas1 {

  object Move {
    def fromString(arg: String): Option[Move] = arg match {

      case s if arg.startsWith("R") || arg.startsWith("L") =>
        try {

          val turn = if(arg.charAt(0) == 'R') Right else Left

          Some(Move(arg.substring(1).toInt, turn))
        }
        catch {
          case e: Exception =>
            None
        }

      case _ => None
    }
  }

  case class Move(times: Int, direction: Turn)

  val testInput = "R4, R5, L5, L5, L3, R2, R1, R1, L5, R5, R2, L1, L3, L4, R3, L1, L1, R2, R3, R3, R1, L3, L5, R3, R1, L1, R1, R2, L1, L4, L5, R4, R2, L192, R5, L2, R53, R1, L5, R73, R5, L5, R186, L3, L2, R1, R3, L3, L3, R1, L4, L2, R3, L5, R4, R3, R1, L1, R5, R2, R1, R1, R1, R3, R2, L1, R5, R1, L5, R2, L2, L4, R3, L1, R4, L5, R4, R3, L5, L3, R4, R2, L5, L5, R2, R3, R5, R4, R2, R1, L1, L5, L2, L3, L4, L5, L4, L5, L1, R3, R4, R5, R3, L5, L4, L3, L1, L4, R2, R5, R5, R4, L2, L4, R3, R1, L2, R5, L5, R1, R1, L1, L5, L5, L2, L1, R5, R2, L4, L1, R4, R3, L3, R1, R5, L1, L4, R2, L3, R5, R3, R1, L3"

  val turnsFromInput = testInput.split(", ").flatMap { Move.fromString }

  sealed trait Facing
  object North extends Facing
  object South extends Facing
  object West extends Facing
  object East extends Facing

  sealed trait Turn
  object Left extends Turn
  object Right extends Turn

  // assume an x,y grid where x runs west to east left to right
  // and y is south to north bottom to top
  case class Position(x: Int, y: Int, facing: Facing) {
    def blocksAway = Math.abs(x) + Math.abs(y)
  }

  def executeTurn(currentFace: Facing, direction: Turn): Facing = direction match {

    case Right =>
      currentFace match {
        case North => East
        case East => South
        case South => West
        case West => North
      }
    case Left =>
      currentFace match {
        case North => West
        case West => South
        case South => East
        case East => North
      }
  }

  def executeMove(currentPos: Position, turn: Move): Position = {

    val turned = currentPos.copy(facing = executeTurn(currentPos.facing, turn.direction))

    turned.facing match {
      case North =>
        turned.copy(y = turned.y + turn.times)
      case South =>
        turned.copy(y = turned.y - turn.times)
      case West =>
        turned.copy(x = turned.x - turn.times)
      case East =>
        turned.copy(x = turned.x + turn.times)

    }
  }

  val sampleTurns = "R2, L3".split(", ").flatMap { Move.fromString }

  def blocksAwayFromTurns(moves: Seq[Move]): Int = {
    val finalPos = moves.foldLeft(Position(0,0,North)){
      (acc,move) =>
        executeMove(acc,move)
    }

    finalPos.blocksAway
  }

  assert(blocksAwayFromTurns(sampleTurns) == 5)
  
}