How to do mandatory check that records should be created in Subgrid(Contact) to every Account?

I have a requirement like below

Whenever user create/update account, it should be validated with creating at least 4 contact records for each Product(lookup), if < 4 then throw exception.

For Eg: User just creates Account X for Product A then after sometime user opening same Account X when we need to do a check if he created at least 4 contacts (it's a subgrid in Account entity) for Product A in Account, if < 4 contacts created then throw alert and not allowing to save the Account X

We have 4 types of contact (eg: Contact C1,C2,C3,C4) record for each Product and each Account so it is mandatory to create

It'd be great if anyone share how to check this using plugin. Thanks in advance.