"""Product identity: stable fingerprints and GTIN validation.

Global identity uses ONLY stable attributes (normalized description, brand, unit,
package quantity, GTIN). Fiscal/company context (CFOP, CSOSN, CST, rate, ST, tenant)
never participates: those vary per context and must not merge distinct knowledge.
"""
import hashlib
import re
import unicodedata

from ..classification import ENGINE_VERSION  # noqa: F401  (re-exported for the AI layer)


def normalize_description(value) -> str:
    """NFKD -> ascii -> A-Z0-9 tokens, space-joined (same canonical form as classification)."""
    text = unicodedata.normalize("NFKD", str(value or "")).encode("ascii", "ignore").decode().upper()
    return " ".join(re.sub(r"[^A-Z0-9]+", " ", text).split())


def _normalize_token(value) -> str:
    return normalize_description(value)


def _normalize_quantity(value) -> str:
    digits = re.sub(r"[^0-9.,]", "", str(value or ""))
    if not digits:
        return ""
    try:
        number = float(digits.replace(",", "."))
    except ValueError:
        return digits
    return f"{number:g}"


def product_fingerprint(description, brand=None, unit=None, package_quantity=None) -> str:
    parts = [_normalize_token(description), _normalize_token(brand), _normalize_token(unit), _normalize_quantity(package_quantity)]
    return hashlib.sha256("|".join(parts).encode("utf-8")).hexdigest()


def _stem(token: str) -> str:
    """Minimal Portuguese plural stemming so AGUAS matches AGUA / MINERAIS matches MINERAL."""
    if len(token) > 4 and token.endswith("AIS"):
        return token[:-3] + "AL"
    if len(token) > 4 and token.endswith("ES"):
        return token[:-2]
    if len(token) > 3 and token.endswith("S"):
        return token[:-1]
    return token


def token_stems(value) -> set:
    return {_stem(token) for token in normalize_description(value).split()}


def overlap_score(query, official) -> float:
    """Fraction of query description stems present in the official description stems."""
    stems = token_stems(query)
    if not stems:
        return 0.0
    return len(stems & token_stems(official)) / len(stems)


def validate_gtin(value) -> str | None:
    """Returns the canonical GTIN when the checksum is valid, else None.
    Accepts GTIN-8/12/13/14 (EAN-8/UPC-12/EAN-13/GTIN-14)."""
    digits = re.sub(r"\D", "", str(value or ""))
    if len(digits) not in (8, 12, 13, 14):
        return None
    total = 0
    for index, char in enumerate(reversed(digits)):
        digit = int(char)
        total += digit * (1 if index % 2 == 0 else 3)
    if total % 10 != 0:
        return None
    return digits