describe('Rover', () => {

    describe('Turn left', () => {
        it('North -> L -> West', () => {
            expect(turn('N', 'L')).toBe('W');
        });

        it('West -> L -> South', () => {
            expect(turn('W', 'L')).toBe('S');
        });

        it('South -> L -> East', () => {
            expect(turn('S', 'L')).toBe('E');
        });

        it('East -> L -> North', () => {
            expect(turn('E', 'L')).toBe('N');
        });
    });

    describe('Turn right', () => {
        it('East -> R -> South', () => {
            expect(turn('E', 'R')).toBe('S');
        });

        it('South -> R -> West', () => {
            expect(turn('S', 'R')).toBe('W');
        });

        it('West -> R -> North', () => {
            expect(turn('W', 'R')).toBe('N');
        });

        it('North -> R -> East', () => {
            expect(turn('N', 'R')).toBe('E');
        });
    });

    describe('Moving', () => {
        it('1 1 N -> M -> 1 2 N', () => {
           let newPosition = nextPosition({ x:1, y:1, orientation:'N' }, 'M');
           expect(newPosition).toEqual({x:1, y:2, orientation:'N'});
        });

        it('1 1 E -> M -> 2 1 E', () => {
            let newPosition = nextPosition({ x:1, y:1, orientation:'E' }, 'M');
            expect(newPosition).toEqual({x:2, y:1, orientation:'E'});
        });

        it('1 1 E -> L -> 1 1 N', () => {
            let newPosition = nextPosition({ x:1, y:1, orientation:'E' }, 'L');
            expect(newPosition).toEqual({x:1, y:1, orientation:'N'});
        });

    });

});

const orientations = ['N','W','S','E'];
const moves = {
    N: position => {
        return {
            'x': position.x,
            'y': position.y + 1,
            orientation: 'N'
        }
    },
    E: position => {
        return {
            'x': position.x + 1,
            'y': position.y,
            orientation: 'E'
        }
    }
};

function turn(currentOrientation, command) {
    let index = orientations.indexOf(currentOrientation);
    let nextIndex = command === 'R' ? index -1 : index + 1;
    return orientations[(nextIndex + 4) % 4];
}

function nextPosition(currentPosition) {
    return move(currentPosition);
}

function move(currentPosition) {
    return moves[currentPosition.orientation](currentPosition);
}