logistics.sscc

def build_sscc(extension_digit: int, company_prefix: str, serial_reference: int) -> str

from fune.logistics.sscc import build_sscc  # logistics.sscc@^1

import re

_PREFIX = re.compile(r"^[0-9]{4,12}$")


def _whole(value: object) -> bool:
    return isinstance(value, int) and not isinstance(value, bool)


def build_sscc(extension_digit: int, company_prefix: str, serial_reference: int) -> str:
    """Build an 18-digit SSCC: extension digit, GS1 company prefix, zero-padded
    serial reference and GS1 mod-10 check digit."""
    if not _whole(extension_digit) or extension_digit < 0 or extension_digit > 9:
        raise ValueError("extensionDigit must be 0 to 9, received %r" % (extension_digit,))
    # fullmatch, not match: "$" in re also matches before a trailing newline.
    if not isinstance(company_prefix, str) or not _PREFIX.fullmatch(company_prefix):
        raise ValueError('companyPrefix must be 4 to 12 digits, received "%s"' % (company_prefix,))
    if not _whole(serial_reference):
        raise TypeError("serialReference must be an integer, received %r" % (serial_reference,))
    if serial_reference < 0:
        raise ValueError("serialReference must not be negative, received %d" % serial_reference)
    # Prefix and serial share 16 digits, so a longer prefix leaves less room.
    # Too large is an error: truncating would reuse another unit's number.
    room = 16 - len(company_prefix)
    serial = str(serial_reference)
    if len(serial) > room:
        raise ValueError(
            "serialReference must fit in %d digits after a %d-digit company prefix, received %d"
            % (room, len(company_prefix), serial_reference)
        )
    data = str(extension_digit) + company_prefix + serial.rjust(room, "0")

    # GS1 mod-10: weights 3, 1, 3, 1 ... from the rightmost data digit leftwards.
    # validation.gtin does the same sum but only exports validate_gtin, which
    # takes 8 to 14 digits, not an 18-digit SSCC.
    total = 0
    weight = 3
    for ch in reversed(data):
        total += (ord(ch) - 48) * weight
        weight = 1 if weight == 3 else 3
    return data + str((10 - total % 10) % 10)

Install

fune build

With that line in your source, in a Python project (language python in fune.project), fune build resolves it and nothing else, pins them in fune.lock, downloads only the Python package of each, and builds the code above into your project’s .fune/build, one readable file per capability with a header linking back here. Or pin a range in fune.project and build in one step:

fune add logistics.sscc

The manifest, vectors and README with only the Python implementation. Install it without the registry with fune add ./logistics.sscc-1.0.0-python.fune, or fetch it from a terminal with fune pull logistics.sscc@1.0.0:python.

The whole function, every language, is one file too: logistics.sscc-1.0.0.fune, 11,838 bytes, sha256 073616835887c024668390f51220564385095dcf3ead76172e71b17798111f3c. It installs into a project of any language.

# fune: before logistics.sscc

# fune: after logistics.sscc

# fune: step logistics.sscc after <n|label>

More from the author

So a 7-digit prefix leaves 9 digits of serial reference and a 10-digit prefix leaves 6. A serial reference too large for the room left is an error rather than being truncated, because a truncated serial silently re-uses another pallet's number.

## Check digit

The standard GS1 mod-10: weight the 17 data digits 3, 1, 3, 1 ... starting from the rightmost and moving left, sum, and the check digit brings the sum up to a multiple of ten. It is the same arithmetic as `validation.gtin`, but that capability only exports `validateGtin`, which accepts 8, 12, 13 and 14 digits and so cannot be handed an 18-digit SSCC; the three lines of arithmetic are repeated here rather than widening another package's API. GS1's own example, `(00) 1 0614141 123456789 7`, is a vector.

## What it does not do

- It returns the bare 18 digits. The label's human-readable line shows them after the application identifier as `(00) 106141411234567897`; the barcode (GS1-128) encodes `00` followed by the 18 digits. - It does not allocate serial references. GS1 asks that an SSCC is not re-used for at least a year after the unit was shipped; keeping the counter is the caller's job. - It cannot tell whether a prefix was really allocated to you.

## Source

GS1 General Specifications, the SSCC (logistic units) and check digit calculation sections, https://www.gs1.org/standards/barcodes-epcrfid-id-keys/gs1-general-specifications ; GS1 UK, "How do I create SSCCs and logistics labels?", https://www.gs1uk.org/knowledge-hub/barcodes/how-do-i-create-ssccs-and-logistics-labels

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