Sign-Up Username suggestions when username is already used

Hi guys,

All major websites out there, while Signing-up, they validate the given username and if it is already used they suggest available Usernames (“related” to the one you initially given)
Given: “Tasos” (Exists in database)
Suggestions: “Tasos1973” , “Tasoss”, “Tasos1”, etc (Do not exist in database)

I would like to know how would you build that “Username suggestions” part of Sign-up.
(I work on php but doesn’t really matter, I just need to see the workaround and go from there)

Thank in advance