SEO friendly country IP redirection?

I have a german shop at example.com/de and the same shop in english at example.com/en.
If a visitor from germany visit example.com , I want that this visitor will be redirected to example.com/de.
If a visitor from USA visit example.com , I want that this visitor will be redirected to example.com/en.
Important:
If a visitor from germany visit example.com/en , I want that this visitor will NOT be redirected to example.com/de.
If a visitor from USA visit example.com/de , I want that this visitor…
SEO friendly country IP redirection?

See original post by marcom