Rewiring Outdoor Light to Switched Outlet (half hot, half not)

I have an outdoor light that's currently controlled via a light switch inside the house, that I would like to convert into a switched outlet (half hot, half controlled via the existing light switch).

However, I'm not sure if it's even possible… I opened up the outdoor light and there are three wires coming from the wall (black, white and ground). Each of these wires have a pigtail with another wire added that is then connected to the outdoor light.

Advice appreciated!