snake.dart

#import('dart:html');


void main() {
  new Game().run();
}

class Game {
  CanvasRenderingContext2D ctx = null;
  CanvasElement canvas = null;
  var xrand = 0.0, yrand = 0.0;
  int randCount = 1;
  Snake snake = null;
  
  Game() {
    this.initialize();
  }

  void initialize() {
    // Canvas
    this.canvas         = document.query("#canvas");
    this.ctx            = canvas.getContext("2d");
    this.ctx.fillStyle  = "rgb(200,0,0)";
    this.snake          = new Snake(this.canvas.width, this.canvas.height);
    // Register keylistener
    document.on.keyDown.add(handleEvent);
  }
  
  void run() {
    window.setInterval(moveSnake, 100); // Draw a running snake for every 100 ms
    
    // Make food and start the snake
    this.makeFood();
    this.snake.paint(this.ctx);
  }
  
  void handleEvent(event) {
    int keycode = 0;
    keycode = event.keyCode;

    switch (keycode) {
      // Left
      case 37:
        this.snake.moveLeft();
        break;
      // Up
      case 38:
        this.snake.moveUp();
        break;
      // Right
      case 39: 
        this.snake.moveRight();
        break;
      // Down
      case 40:
        this.snake.moveDown();
        break;
    }
    
    if (this.snake.x == this.xrand && this.snake.y == this.yrand) {
      this.makeFood();
      this.snake.snakeLength = this.snake.snakeLength + 1;
    }
    
    this.snake.paint(this.ctx);
  }

  void moveSnake() {
    switch (this.snake.direction) {
      case 'left':
        this.snake.moveLeft();
        break;
      case 'up':
        this.snake.moveUp();
        break;
      case 'right':
        this.snake.moveRight();
        break;
      case 'down':
        this.snake.moveDown();
        break;
    }
    if (this.snake.x == this.xrand && this.snake.y == this.yrand) {
      this.makeFood();
      this.snake.snakeLength = this.snake.snakeLength + 1;
    }

    this.snake.paint(this.ctx);
  }

  
  
  /**
   *  Method creates the food for snake at random location on the canvas.
   */
  void makeFood() {
    double rem = 0.0;
    // Get the random location for food and trim it
    this.xrand = (this.getRandom() * (this.canvas.width)).floor();
    this.yrand = (this.getRandom() * (this.canvas.height)).floor();
    rem = this.xrand % this.snake.gridSize;
    this.xrand = this.xrand - rem;
    rem = this.yrand % this.snake.gridSize;
    this.yrand = this.yrand - rem;
    // Draw it!
    this.ctx.fillStyle = "rgb(10,100,0)";
    this.ctx.fillRect(xrand, yrand, this.snake.gridSize, this.snake.gridSize);
  }
  
  /**
   * Workaround to generate random number for a bug in Math.random() method in DART.
   */
  double getRandom() {
    double rand = 0.0;
    for (int i = 0; i < this.randCount; i++) {
      rand = Math.random();
    }
    this.randCount = this.randCount + 1;
    return rand;
  }
  
}



class Snake {
  var snakeBody = null;
  int x = 0;
  int y = 0;
  int gridSize = 20;
  String direction = "right";
  
  int snakeLength = 3; // Default snake length
  
  // Bounds
  int maxWidth = 0;
  int maxHeight = 0;

  Snake(int mxWidth, int mxHeight) {
    this.snakeBody = [];
    this.maxWidth = mxWidth;
    this.maxHeight = mxHeight;
  }
  
  /**
   * Method to draw a snake. 
   */
  void paint(CanvasRenderingContext2D ctx) {
    var coord = null;

    // Precondition check.
    if (this.snakeBody == null) return;
    if (ctx == null) return;

    coord = [this.x, this.y];
    this.snakeBody.add(coord);
    ctx.fillStyle = "rgb(200,0,0)";
    ctx.fillRect(this.x, this.y, this.gridSize, this.gridSize); 
    
    
    if (this.snakeBody.length > this.snakeLength) {
      var itemToRemove = this.snakeBody[0];
      this.snakeBody.removeRange(0, 1);
      ctx.clearRect(itemToRemove[0], itemToRemove[1], this.gridSize, this.gridSize);
    }

  }
  
  void moveUp() {
    if (this.getUpPos() >= 0) {
      this.executeMove('up', 'y', this.getUpPos());
    } else {
      this.whichWay('x');
    }
  }
  
  void moveDown() {
    if (this.getDownPos() < this.maxHeight) {
      this.executeMove('down', 'y', this.getDownPos());
    } else {
      this.whichWay('x');
    }
  }
  
  void moveLeft() {
    if (this.getLeftPos() >= 0) {
      this.executeMove('left', 'x', this.getLeftPos());
    } else {
      this.whichWay('y');
    }
  }
  
  void moveRight() {
    if (this.getRightPos() < this.maxWidth) {
      this.executeMove('right', 'x', this.getRightPos());
    } else {
      this.whichWay('y');
    }
  }
  
  void executeMove(dirValue, axisType, axisValue) {
    this.direction = dirValue;
    if (axisType == 'x') {
      this.x = axisValue;
    } else if (axisType == 'y') {
      this.y = axisValue;
    }
  }
  
  /**
   * Method to decide which direction inwhich snake has to move when it hits the border.
   */
  whichWay(axisType) {
    if (axisType == 'x') {
      return (this.x > this.maxWidth / 2) ? this.moveLeft() : this.moveRight();
    } else if (axisType == 'y') {
      return (this.x > this.maxHeight / 2) ? this.moveUp() : this.moveDown();
    }
  }
  
 
  int getLeftPos() {
    return this.x - this.gridSize;
  }
  
  int getRightPos() {
    return this.x + this.gridSize;
  }
  
  int getUpPos() {
    return this.y - this.gridSize;
  }
  
  int getDownPos() {
    return this.y + this.gridSize;
  }

}