I did a power meter using CT and PT, and filter the rectified AC voltage at the output of each transformer, and the maximum value of voltage or current line as related to 5Vdc, the conditioning circuit output, which is connected an ADC. This is the easiest way and with less precision. There is another which is taking N samples and to obtain the average value.
To measure the F.P. circuits need zero-crossing detector for current and voltage, usually gets a high resistance connected to a interruption of the microcontroller, and measures the time it takes a interrupcion with the other.