#6 coding dojo

ant.js

var white = 'x';
var black = 'y';

var north = {o:"N"};
var east = {o:"E"};
var south = {o:"S"};
var west = {o:"W"};
north.right = function() { return east; }
north.left = function() { return west; }
east.right = function() { return south;}
east.left = function() { return north;}
south.right = function() { return west;}
south.left = function() { return east;}
west.right = function() { return north;}
west.left = function() { return south;}

function anyOrientation() {
  return north;
}

function anyPosition() {
  return [0,0];
}

var Ant = function () {
  this.orientation = north;
}; 

Ant.prototype = {
  move: function (plane) {
    var color = plane.getColorAtPosition(this.position);
    var newColor = color == black ? white : black;
    plane.setColorAtPosition(this.position, newColor);
    this.position = [1,1];  
    this.orientation = this.orientation.right();
    // this.orientation = color == white 
    //   ? this.orientation.right()
    //   : this.orientation.left();
  } 
};

var Plane = function() {};
Plane.prototype = {
  setColorAtPosition: function (position, color) {
    this[position] = color;
  },
  getColorAtPosition: function (position) {
    return this[position] || white;
  }
};

// At a white square, turn 90° right, flip the color of the square, move forward one unit
// At a black square, turn 90° left, flip the color of the square, move forward one unit

describe("langton's ant", function() {
  describe("At a white square", function() {
    var ant;
    var plane;
    var position;
    var originalOrientation;
    
    beforeEach(function() {
      ant = new Ant();
      plane = new Plane();
      position = anyPosition();
      originalOrientation = anyOrientation();
      plane.setColorAtPosition(position, white);
    });
      
    it("turn 90° right", function() {
      ant.orientation = originalOrientation;
      ant.move(plane);
      expect(ant.orientation).
        toBe(originalOrientation.right());
    });
    it("flip the color of the square", function() {
      ant.position = position;
      ant.move(plane);
      expect(plane.getColorAtPosition(position)).
        toBe(black);
    });
    it("move forward one unit", function() {
      ant.position = position;
      ant.move(plane);
      expect(ant.position).not.toBe(position);
    });
  });

  xdescribe("At a black square", function() {
    var ant;
    var plane;
    var position;
    var originalOrientation;
    
    beforeEach(function() {
      ant = new Ant();
      plane = new Plane();
      position = anyPosition();
      originalOrientation = anyOrientation();
      plane.setColorAtPosition(position, black);
    });
    
    it('turn 90° left', function() {
      ant.orientation = originalOrientation;
      ant.move(plane);
      expect(ant.orientation).
        toBe(originalOrientation.left());
    });
  });
  
  describe("orientation", function() {
    it('supports turn 90 right', function() {
      expect(north.right()).toBe(east);
      expect(east.right()).toBe(south);
      expect(south.right()).toBe(west);
      expect(west.right()).toBe(north);
    });   
    
    it('supports turn 90 left', function() {
      expect(north.left()).toBe(west);
      expect(east.left()).toBe(north);
      expect(south.left()).toBe(east);
      expect(west.left()).toBe(south);
    }); 
  });


  describe("plane", function() {
    var plane;
    
    beforeEach(function() {
      plane = new Plane();
    });

    it('has default color white', function() {
      expect(plane.getColorAtPosition(anyPosition())).
        toBe(white);
    });   
    
    it('supports change of color at position', function() {
      expect(north.left()).toBe(west);
      expect(east.left()).toBe(north);
      expect(south.left()).toBe(east);
      expect(west.left()).toBe(south);
    }); 
  });
});

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