Help with using DL and user32.dll to get the active window

I’m still new to ruby and am having trouble working out how to access
windows API with DL

So far my code looks like this:

require “dl”
user32 = DL.dlopen(‘user32’)
actwindow =[‘GetActiveWindow’],type=DL::TYPE_VOID,

I realise .call my argument is an empty array, I’m not sure what
arguments I should be sending when
the ‘GetActiveWindow’ method is TYPE_VOID
Any hits in the right direction would be highly appreciated!

GetActiveWindow →