pii/checksums.py

"""Validateurs et generateurs d'identifiants francais a checksum.

Ces fonctions servent deux usages :
- generation de PII valides pour le corpus synthetique (bench)
- plus tard, la couche A de detection (un match regex + checksum OK = decision)
"""

import random
import string

# ---------------------------------------------------------------- Luhn (CB, SIREN, SIRET)


def luhn_checksum(digits: str) -> int:
    total = 0
    for i, ch in enumerate(reversed(digits)):
        d = int(ch)
        if i % 2 == 1:
            d *= 2
            if d > 9:
                d -= 9
        total += d
    return total % 10


def luhn_valid(digits: str) -> bool:
    return digits.isdigit() and luhn_checksum(digits) == 0


def _luhn_complete(prefix: str) -> str:
    """Ajoute le digit de controle rendant prefix+d valide au sens de Luhn."""
    check = (10 - luhn_checksum(prefix + "0")) % 10
    return prefix + str(check)


def gen_siren(rng: random.Random) -> str:
    return _luhn_complete("".join(rng.choices(string.digits, k=8)))


def gen_siret(rng: random.Random, siren: str | None = None) -> str:
    """SIRET = SIREN + NIC (5 chiffres), le tout valide Luhn sur 14 chiffres."""
    siren = siren or gen_siren(rng)
    nic4 = "".join(rng.choices(string.digits, k=4))
    return _luhn_complete(siren + nic4)


def siren_valid(s: str) -> bool:
    return len(s) == 9 and luhn_valid(s)


def siret_valid(s: str) -> bool:
    return len(s) == 14 and luhn_valid(s)


def gen_carte_bancaire(rng: random.Random) -> str:
    prefix = rng.choice(["4", "51", "52", "53", "54", "55"])  # Visa / MC
    body = "".join(rng.choices(string.digits, k=15 - len(prefix)))
    return _luhn_complete(prefix + body)


# ---------------------------------------------------------------- NIR (n° de securite sociale)

_NIR_DEPTS = [f"{d:02d}" for d in range(1, 96) if d != 20] + ["2A", "2B", "97"]


def nir_key(nir13: str) -> int:
    """Cle = 97 - (NIR mod 97). Corse : 2A -> -1e6, 2B -> -2e6 sur le nombre."""
    s = nir13.upper()
    if "A" in s:
        n = int(s.replace("A", "0")) - 1_000_000
    elif "B" in s:
        n = int(s.replace("B", "0")) - 2_000_000
    else:
        n = int(s)
    return 97 - (n % 97)


def gen_nir(rng: random.Random) -> str:
    """NIR complet 15 caracteres (13 + cle), checksum valide, Corse incluse."""
    sexe = rng.choice("12")
    annee = f"{rng.randint(0, 99):02d}"
    mois = f"{rng.randint(1, 12):02d}"
    dept = rng.choice(_NIR_DEPTS)
    commune = f"{rng.randint(1, 990):03d}"
    ordre = f"{rng.randint(1, 999):03d}"
    nir13 = sexe + annee + mois + dept + commune + ordre
    return nir13 + f"{nir_key(nir13):02d}"


def nir_valid(s: str) -> bool:
    s = s.replace(" ", "").upper()
    if len(s) != 15:
        return False
    nir13, key = s[:13], s[13:]
    if not key.isdigit():
        return False
    core = nir13.replace("A", "").replace("B", "")
    if not core.isdigit() or len(core) < 12:
        return False
    return nir_key(nir13) == int(key)


# ---------------------------------------------------------------- IBAN


def _iban_mod97(iban: str) -> int:
    rearranged = iban[4:] + iban[:4]
    num = "".join(str(int(c, 36)) for c in rearranged)
    return int(num) % 97


def iban_valid(s: str) -> bool:
    s = s.replace(" ", "").upper()
    if len(s) < 15 or not s[:2].isalpha() or not s[2:4].isdigit():
        return False
    return _iban_mod97(s) == 1


def gen_iban_fr(rng: random.Random) -> str:
    """IBAN FR : FRkk BBBBB GGGGG CCCCCCCCCCC KK (cle RIB + cle IBAN valides)."""
    banque = "".join(rng.choices(string.digits, k=5))
    guichet = "".join(rng.choices(string.digits, k=5))
    compte = "".join(rng.choices(string.digits, k=11))
    cle_rib = 97 - ((89 * int(banque) + 15 * int(guichet) + 3 * int(compte)) % 97)
    bban = f"{banque}{guichet}{compte}{cle_rib:02d}"
    check = 98 - _iban_mod97(f"FR00{bban}")
    return f"FR{check:02d}{bban}"


# ---------------------------------------------------------------- TVA intracommunautaire FR


def gen_tva_fr(rng: random.Random, siren: str | None = None) -> str:
    siren = siren or gen_siren(rng)
    key = (12 + 3 * (int(siren) % 97)) % 97
    return f"FR{key:02d}{siren}"


def tva_fr_valid(s: str) -> bool:
    s = s.replace(" ", "").upper()
    if len(s) != 13 or not s.startswith("FR") or not s[2:].isdigit():
        return False
    siren = s[4:]
    return int(s[2:4]) == (12 + 3 * (int(siren) % 97)) % 97 and siren_valid(siren)