Select/highlight region in insert mode

Hello !

Developer of Neogen here, I’m considering allowing this feature:

This is basically writing some text in the file, like [TODO: description], and I would want to jump my cursor into [ in insert mode, highlighting all region: [TODO: description], and replacing it with what I’m writing in insert mode.
I wanted to do that with a Lua API, but it does not seem to exist.

Do you have any ideas ?