Automatically turn off cellular when on wifi?

I'm looking for recommendations. I'd like to automatically turn off my cellular modem whenever I'm attached to a good Wi-Fi signal. Airplane mode on demand.

My rationale is multiple: I'd like to save battery life when I don't need it. I don't need phone calls or SMS. Everything goes over the internet for me anyway.

I would like to reduce my exposure to cellular security problems, and location tracking.

Ideally whatever implements this would be open source.

--- edit ---- Using the word modem was probably wrong in the post. I want to turn the cellular features off. No mobile data, no mobile phone calls, no mobile text, I would like the cellular part of the phone to be powered off.