Hi SY,
Your English is much better than my Turkish.
As Alec said in post #4, directly measuring mains voltages of 220V is dangerous and the best approach would be to use a current transformer to isolate you measuring electronics from the mains supply. A current transformer can be very accurate, but it all depends on what current range you want. 0 Amps to 1A upwards should not be a problem.
But if you must use a resistor in the grid line there are two methods, as you say:
(1) Low side
(2) High side
I am not sure why you say that low side is more dangerous; I would have thought that high side was the more dangerous, and more difficult to implement.
The best approach, in my opinion is to have the current measuring circuit, either high side or low side referenced to the mains supply, and completely protected from human touch.
The current measuring circuit then communicates with your single board computer (SBC) via a serial link, normally I2C or SPI, but possibly asynchronous serial.
The communications link between the sense circuit and the SBC would then be isolated either optically, capacitively, or inductively.
There are low cost and simple to use chips for all these functions.
One small complication is that you will need a precision rectifier to convert the AC current into a DC voltage.
If you favor the above approach let us know and we can take it from there.
spec