Restrict members to join one group at a time.

Hi, I want the people who sign up on my website to be able to join only one group at a time and then be allowed access to contents restricted only to that particular group.
For example, I have created 10 different groups which have corresponding contents restricted to it (say group A has access to certain images, group B has access to certain videos, group C has certain audios and so on) and have a registration redirect page where the members can select and join only one group from the list of the 10 groups (using the [groups_join] shortcode).
Now I wanna know how do I restrict members on my website to join only a single group at a time and perhaps show them a warning message if they select or try to join another group?