Update ProductLoadAllPaged stored procedure to sort by bestseller

Hi,

Is someone capable of update stored procedure ProductLoadAllPaged to add option to sort by bestseller ?
I want to add function to order by bestseller for example ?orderby=20

Something like:

---------
ELSE IF @OrderBy = 20 /* Bestseller */

SET @sql_orderby = '?'
---------

I studied about it but it is beyond my skills. Actual coding is not cappable to consider bestseller, so i cannot add something easy to implement. It need to expand code with additional tables i pressume.

Do someone try to solve this ?

Thanks for your reactions.