What sensor were you planning on using?
The issue with using the RasPi is that it has no analog inputs, so finding an AC voltage sensor with integrated ADC would be best and then you just interface it to one of the serial buses.
One option is to take an AC to DC transformer and remove any internal regulator then use something like an ADS1115 interfaced to the I2C bus on the RasPi. The DC output voltage would be proportional to the AC input and you could reduce it down to work within the max range of the ADC with a simple resistor divider.
@wmontg5988 I believe was talking about the SCT013 current sensor which could be interfaced in a similar way to measure the current draw.
As @tad.dvor mentioned, measuring line voltage is dangerous and not recommended unless you are experienced with electrical equipment. I certainly wouldn’t recommend any solution where you are not isolated from the mains like a lot of the AC to USB power adapters. A transformer is good as it isolates, and you probably have one already in the junk box you could crack open and bypass the regulator after the bridge rectifier. Then RTV it all back together so it’s pretty and safe.
Cheers,
Craig