package 
{
  import flash.display.Sprite;
  import flash.events.Event;
  import flash.events.TimerEvent;
  import flash.utils.Timer;
  
  [SWF(backgroundColor = '0xCCCCCC', width = '400', height = '300', frameRate="50")]
  
  public class Main extends Sprite
  {
    private const FPS:               Number = stage.frameRate;
    private const BALL_BORDER_WIDTH: uint   = 1;
    private const BALL_BORDER_COLOR: uint   = 0x000000;
    private const BALL_COLOR:        uint   = 0x55AA55;
    
    private var v_width:  Number = 400; // = stage.width
    private var v_height: Number = 300; // = stage.height
    
    private var v_ball_r:  Number = 8;
    private var v_ball_x:  Number = v_width/2;
    private var v_ball_y:  Number = v_height/2;
    private var v_ball_vx: Number = (Math.random()<0.5?1:-1)*( 50 + Math.random()*100);
    private var v_ball_vy: Number = (Math.random()<0.5?1:-1)*(100 + Math.random()* 50);
    
    private var v_ball: Sprite;
    
    public function Main()
    {
      v_ball = new Sprite();
      v_ball.graphics.lineStyle(BALL_BORDER_WIDTH, BALL_BORDER_COLOR);
      v_ball.graphics.beginFill(BALL_COLOR);
      v_ball.graphics.drawCircle(0, 0, v_ball_r);
      v_ball.width = v_ball.height = 2*v_ball_r;
      
      addChild( v_ball );
      
      m_draw();
      
      this.addEventListener(Event.ENTER_FRAME, o_redraw);
    }
    
    private function m_draw(): void 
    {
      v_ball.x = v_ball_x;
      v_ball.y = v_ball_y;
    }
    
    private function o_redraw(p_event: Event): void 
    {
      // collision detection
      if (v_ball_x <= v_ball_r || v_ball_x >= v_width  - v_ball_r)
        v_ball_vx = -v_ball_vx;
      if (v_ball_y <= v_ball_r || v_ball_y >= v_height - v_ball_r)
        v_ball_vy = -v_ball_vy;
      
      // move ball
      v_ball_x += v_ball_vx/FPS;
      v_ball_y += v_ball_vy/FPS;
      
      //draw ball
      m_draw();
    }
  }
}