Wall outlet / DC inverter transfer switch

[electr0de]

I am attempting to create a power supply switching device that will automatically and instantly switch from the wall outlet to a DC inverter connected to a car battery when utility power is lost.  I am confused as to how to build this though as I have very limited experience, so forgive me if my current plan is flawed and incorrect. 

Here is a basic block diagram:

Yes the point of this is to be able to play video games when the power is out .

Where the 120V wall line splits and goes to the logic circuit, this is what I am planning and I am certain something is wrong which is what my questions are about:


I know I will need a voltage divided by the transistor inputs but I don't know how to implement it.
So is this possible to achieve using the method shown or do I need to do something totally different?  I am also uncertain of what to do where the question marks are, as in whether it should be grounded or connected to something.  Are there transistors that can be used for this application and how expensive are they? Any help that can be provided is most appreciated.

Thanks a bunch!