Share Window, WindowLeft & WindowRight implementation internally

[Orace]

This is a fork of #629 and #627.

We should introduce a private method to share the implementation among the three Window* methods.

[atifaziz]

I haven't done a study of whether it would help or not but if you'd like to take a crack at this through a PR then I'd be happy to review it. If you'd rather that I first do a study and accept this with conviction (so you don't risk wasting time with work that may not get merged) then you'll have to be patient as this is not going to be a high priority for me.