WooCommerce Limit Cart to one category

Hi,

If a user on my site orders from one category I want to by able to prevent them from adding anything to the cart from another category, any ideas on how I could do this. Effectively when they click Add Cart I need it to check if there are any items in the cart already from another category, if so, get the normal popup that says the items been added to the cart to display a message and not add the item to the cart.

Anyone any ideas how to best approach this?

Cheers,

Lee