Greek AMKA

What it covers

Returns a valid Greek AMKA (social-security number) with a correct Luhn check digit. Constrain with `sex` and age/birth-date filters (the full birth date is encoded). Contradictory combinations are rejected with a 400. Set `invalid=true` for a deliberately wrong check digit.

How it’s calculated

The 11th digit of a Greek AMKA is a standard Luhn (mod-10) check digit computed over the first ten digits.

Payload (positions 1-10): 0 1 0 1 8 5 2 3 4 7
Walk right to left, doubling the rightmost payload digit first (doubled positions marked *):
pos10 = 7* -> 7*2 = 14 -> 14-9 = 5
pos9  = 4  -> 4
pos8  = 3* -> 3*2 = 6
pos7  = 2  -> 2
pos6  = 5* -> 5*2 = 10 -> 10-9 = 1
pos5  = 8  -> 8
pos4  = 1* -> 1*2 = 2
pos3  = 0  -> 0
pos2  = 1* -> 1*2 = 2
pos1  = 0  -> 0
sum = 5+4+6+2+1+8+2+0+2+0 = 30
check = (10 - (30 mod 10)) mod 10 = (10 - 0) mod 10 = 0

Edge cases

• The 10th digit encodes sex by parity: odd -> male, even -> female. The generator sets it deliberately (sexDigit = random(0..4)*2 + parity) so the reported sex is truthful; the checksum itself does not enforce sex parity.
• The first six digits are a DDMMYY birth-date head; the encodable birth-date range is clamped to 1900-01-01 through 2099-12-31 (two-digit year, no explicit century marker in the number).

Gotchas

• The check digit uses the (10 - (sum mod 10)) mod 10 form: when sum mod 10 is 0 the check digit is 0, not 10. Forgetting the outer mod 10 yields an invalid two-digit result.
• Luhn doubling starts on the RIGHTMOST PAYLOAD digit (position 10), because the check digit is appended to its right and is excluded from the payload. Doubling the wrong alternating set inverts the parity and produces a wrong digit.