I'm looking for some help with a module that I'm making.

I have a form that uploads a file. When a file is uploaded I save the details (filename etc) in a database. I don't need drupal to save any file references for me. What I'm having problems with is, if a file has already been uploaded, ask the user "are you sure you want to proceed, this will override your previous your old file".

What I have so far is http://pastebin.com/DNm84jUR

Any help would be appreciated.