nickname/username automatically generated

I do not want a "username" field in the join form. I want a "username" to be generated automatically on the basis of the First and Last Name. What I mean - if someone's name is "John Doe" his username will be john-doe (but it will not be presented on join form) and his profile address will be /john-doe. If there is another John Doe, his username will be "john-doe-2" (or john-doe2) and so on.

How to do it?

You need a good developer for this