impl/python.py

from .logistics_hs_code_validate_types import HsCodeCheck

_KINDS = {6: "hs", 8: "cn", 10: "taric"}


def _invalid(reason: str) -> HsCodeCheck:
    return HsCodeCheck(
        valid=False, normalised=None, kind=None, chapter=None, heading=None, subheading=None, reason=reason
    )


def validate_hs_code(value: str) -> HsCodeCheck:
    """Check the format of a 6-digit HS, 8-digit CN or 10-digit TARIC/UK
    commodity code. Validators answer rather than raise: a malformed code is
    the answer "no"."""
    if not isinstance(value, str):
        return _invalid("empty")
    chars = []
    for ch in value:
        if ch == " " or ch == ".":
            continue
        # Compare with ASCII explicitly: str.isdigit() accepts full-width digits.
        if ch < "0" or ch > "9":
            return _invalid("bad-character")
        chars.append(ch)
    digits = "".join(chars)
    if not digits:
        return _invalid("empty")
    kind = _KINDS.get(len(digits))
    if kind is None:
        return _invalid("bad-length")

    # Text, not a number: chapter "01" must keep its zero.
    chapter = digits[0:2]
    if chapter == "00":
        return _invalid("bad-chapter")
    if chapter == "77":
        return _invalid("reserved-chapter")
    # 98 and 99 are left to national tariffs, so only a national-length code may use them.
    if chapter in ("98", "99") and kind == "hs":
        return _invalid("national-chapter")
    if digits[2:4] == "00":
        return _invalid("bad-heading")

    return HsCodeCheck(
        valid=True,
        normalised=digits,
        kind=kind,
        chapter=chapter,
        heading=digits[0:4],
        subheading=digits[0:6],
        reason=None,
    )