Prevent adding product to cart based on date comparison
I'm building a conference web site and as part of the site, we offer various paid courses that are happening simultaneously and I don't want the user to be able to add an event (product) to their cart if they already have added a product to the cart that's occurring at the same time. I've created a start date field for which to compare this information but problem is I'm not sure of the best way to build this functionality. I'd like to disable the add to cart button using the Calculate Sell Price event.
Any advice is greatly appreciated.