try.scala

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)
    }
    
}

Simulator(5,5).execute((Orientations.N,(1,2)),List('G','A','G','A','G','A','G','A','A'))