marsrovertest.scala

import org.scalatest.Matchers

case class Point(x: Int, y: Int)

sealed trait Direction

case object N extends Direction

case object S extends Direction

case object W extends Direction

case object E extends Direction

case class Rover(position: Point, direction: Direction) {
  def explore(commands: List[Char]):Rover = commands match {
    case head :: tail => (this match {
      case Rover(_, N) => Rover(Point(0, position.y + 1), N)
      case Rover(_, S) => Rover(Point(0, position.y-1), S)
      case Rover(_, W) => Rover(Point(position.x - 1, 0), W)
      case Rover(_, E) => Rover(Point(position.x + 1, 0), E)
    }).explore(tail)
    case Nil => this
  }


}

class MarsRoverTest extends org.scalatest.FunSpec with Matchers {
  describe("mars rover starting at point 0, 0") {
    val initialPoint = Point(x = 0, y = 0)

    def rover0_0(direction: Direction) = {
      Rover(position = initialPoint, direction = direction)
    }

    it("remains at the same position with the same direction when calles wuth empty command list") {
      val rover = rover0_0(N)
      val emptyCommandList = List()
      val newRover = rover.explore(emptyCommandList)
      newRover shouldEqual rover
    }
    describe("given command forward") {
      val goForward = List('f')
      describe("once") {
        it("moves 1 row up facing north") {
          val rover = rover0_0(N)
          val newRover = rover.explore(goForward)
          newRover shouldEqual Rover(position = Point(x = 0, y = 1), direction = N)
        }
        it("moves 1 row down facing south") {
          val rover = rover0_0(S)
          val newRover = rover.explore(goForward)
          newRover shouldEqual Rover(position = Point(x = 0, y = -1), direction = S)
        }
        it("moves 1 row left facing west") {
          val rover = rover0_0(W)
          val newRover = rover.explore(goForward)
          newRover shouldEqual Rover(position = Point(x = -1, y = 0), direction = W)
        }
        it("moves 1 row right facing east") {
          val rover = rover0_0(E)
          val newRover = rover.explore(goForward)
          newRover shouldEqual Rover(position = Point(x = 1, y = 0), direction = E)
        }
      }
      
      describe("twice") {
          val goForwardTwice = goForward ++ goForward
        it("moves 2 rows up facing north") {
          val rover = rover0_0(N)
          val newRover = rover.explore(goForwardTwice)
          newRover shouldEqual Rover(position = Point(x = 0, y = 2), direction = N)
        }
        it("moves 2 row down facing south") {
          val rover = rover0_0(S)
          val newRover = rover.explore(goForwardTwice)
          newRover shouldEqual Rover(position = Point(x = 0, y = -2), direction = S)
        }
        it("moves 2 row left facing west") {
          val rover = rover0_0(W)
          val newRover = rover.explore(goForwardTwice)
          newRover shouldEqual Rover(position = Point(x = -2, y = 0), direction = W)
        }
        it("moves 2 row right facing east") {
          val rover = rover0_0(E)
          val newRover = rover.explore(goForwardTwice)
          newRover shouldEqual Rover(position = Point(x = 2, y = 0), direction = E)
        }
      }
    }

  }

}