Add product to cart Rules

Hi,

I have a unique category that if the customer add an item of that category to cart, he wont be able to add product from differents categories.
But if one product from a different category is already on cart, he wont be able to add a product from the unique category.

Any ideia how can I do that?

Thanks for the help,

Eduardo

If you want to modify the core code, then you can 'add warnings' in
Libraries\Nop.Services\Orders\ShoppingCartService.cs
  AddToCartAsync()