Clean way for a modular rails app?

Hello,

Right now, my Rails app has a controller with far too many functions.
Some of these functions look like:

def generic_function(params)
  case x
  when "module1"
    return module1_function(params)
  when "module2"
    return module2_function(params)
  [...]
  end
end

I would like to move module1_function (and all other module1 related
stuff) in a separate file. Same thing for module2 (in another
separate file) and so on. What is the proper, clean way to do that?

Thanks,
Karine