It’s not hard. As you know, RPi doesn’t have built-in ADC. However, OSPi has a PCF8591T 4-channel ADC, so one channel can be wired internally to the current sensing circuit for sensing current.
The sensing circuit itself is just a precision (0.2 ohm) resistor combined with op-amp based active rectifier (https://en.wikipedia.org/wiki/Precision_rectifier) used to sense small AC voltage.