Autosuggest Countries

How would you build a function to get a country list for a form for auto suggest? Where would you put it? What would you call it?

 

Basically the js calls the url / function but not sure where to put it. Ideally in app_controller so it can be called from anywhere but it has to be accessed via different admin routing also.

 

I have my logged in user so they have a routing prefix manager so i need a manager_countries function?

 

Any help would be great.

 

Thanks

 

Dave