public function addToCart($id, $name, $price)
    {
        $is_in_cart = false;
        $index = 0;
        foreach ($_SESSION['cart'] as $key => $arr) {
            if ($arr['id'] == $id) {
                $is_in_cart = true;
                $index = $key;
            break;
            }
        }
        if ($is_in_cart) {
            $_SESSION['cart'][$index]['quantity']++;
        } else {
            array_push($_SESSION['cart'], array('id' => $id, 'name' => $name, 'price' => $price, 'quantity' => 1));
        }
        self::$cart = $_SESSION['cart'];
    }