Add products from one category at a time to the cart?

[stephen89]

This is probably beyond my development abilities, which are pretty low, but I like to try things on my own before I find a professional. In any case, I want a customer to only be able to add products from one category at a time, so if they add their first product from Laptops, for example, and then try to add a product from MP3 players, it will give them a warning and not add to the cart, however if they add a second product from laptops, it will add in and everything will be great.

 

Just a quick idea about which files to mess with, where to start and level of difficulty in your opinion would be greatly appreciated.

 

Thank You,

Stephen