display warning message before selecting additional product from same shelf

Hi All,

we want to warning message to pop up if user is requesting for the additional product from same shelf.

for eg. we have shelf called "ABC". and it has product(application groups) assigned as Product1, Product2, Product3 etc.

user has requested for Product1 and has assigned successfully. now user wants to request for Product2 so before adding the request to the cart there should be warning message to be displayed.