xTest.scala

object Application {

  def main(args :Array[String]){
    println(Simulator(5,5).execute((Orientations.N,(1,2)),List('G','A','G','A','G','A','G','A','A')))
    println(Simulator(5,5).execute((Orientations.E,(3,3)),List('A','A','D','A','A','D','A','D','D','A')))

  }
  
  object Orientations {
      type  Orientation=Char
      val N='N'
      val E='E'
      val W='W'
      val S='S'
      val clockWise=List(N,E,S,W)
    
     def next[A](elements:List[A],e:A):Option[A]= elements.drop(elements.indexOf(e)+1).firstOption
     def previous[A](elements:List[A],e:A):Option[A]= elements.take(elements.indexOf(e)).lastOption
   
     def right(o:Orientation)= next(clockWise,o).getOrElse(clockWise.first)
     def left(o:Orientation)= previous(clockWise,o).getOrElse(clockWise.last)
  }

  case class Simulator(bounds:(Int,Int))  {
    import Orientations._    
    type Coordination=(Int,Int)
    type State= (Orientation,Coordination)

    def commandMap(c:Char,s:State):State= {
      val (o,cord)=s
      c match{
      case 'G' => (left(o),cord)
      case 'D'=>(right(o),cord)
      case 'A'=>(o,advance(o,cord))
      }
    }
    def advance(o:Orientation,cord:(Int,Int)):(Int,Int)={
      val (x,y)=cord
      o match {
       case N=> (x,y+1)
       case S=> (x,y-1)
       case W=> (x-1,y)
       case E=> (x+1,y)
      }
    }

    def execute(initial:State,commands:List[Char])=
          commands.foldLeft(initial)((state,c)=>  notOutOfBound(commandMap(c,state)).getOrElse(state))

     def notOutOfBound(s:State):Option[State]={
        val (_,(x,y))=s
        val (maxX,maxY)=bounds
       if (x>maxX||y>maxY) None else Some(s)
     }
    
  }

  
}