Isolation is important. OP says size is important. Therefore OP should:
1) Wind a small transformer with a 10:1 ratio ( 50 to 5 turns) driven by a properly voltage & wattage rated resistor (10 kohm) in series with the primary coil to permit small gauge (30+ AWG) enameled wiring. A scrap toroid from a PC PSU can be rewound. Or even use some soft iron or ferrite rod.
The 10K primary permits around 22mA (@ 4.8Watts) of current, which will go to about 220mA in the secondary. I'd use 10, 1K, 1W resistors in series if space allows.
2) Rectify and regulate the secondary voltage to 5v for the uC power
3) Tap a 50:1 ratio (off a single turn of the secondary) voltage unrectified power to peak at perhaps +/- 6.2V. Then using a full wave bridge as shown here:
**broken link removed**
do not join the outputs of D1 and D3, instead send them to 2 adc inputs via 50/50 resistive voltage dividers (10k - 10k) for sampling. This permits instantaneous sampling and determination of +ve or -ve going AC with a grounded DC reference that the uC uses.