SGTIN-96 to GTIN.py

PARTITION_MAP = {
    0: (40, 12, 4, 1),
    1: (37, 11, 7, 2),
    2: (34, 10, 10, 3),
    3: (30, 9, 14, 4),
    4: (27, 8, 17, 5),
    5: (24, 7, 20, 6),
    6: (20, 6, 24, 7)
}


def calculate_check_digit(gtin):
    '''Given a GTIN (8-14) or SSCC, calculate its appropriate check digit'''
    reverse_gtin = gtin[::-1]
    total = 0
    count = 0
    for char in reverse_gtin:
        digit = int(char)
        if count % 2 == 0:
            digit = digit * 3
        total = total + digit
        count = count + 1
    return 10 - (total % 10)


def combine_gtin_with_check_digit(gtin):
    '''Combine a '''
    return gtin + str(calculate_check_digit(gtin))


def parse_sgtin_96(sgtin_96):
    '''Given a SGTIN-96 hex string, parse each segment.
    Returns a dictionary of the segments as well as the tag URI.

    SGTIN Format (bits):
    Header    Filter  Partition   Company Prefix  Item Reference  Serial
    8         3       3           20-40           24-4            38

    Documentation here:
    http://www.gs1.org/sites/default/files/docs/tds/TDS_1_9_Standard.pdf

    Process:
    - Read the partition data
    - Get item reference length
    - Read item reference, BAM
    '''

    if not sgtin_96:
        raise Exception('Pass in a value.')

    if not sgtin_96.startswith("30"):
        # not a sgtin, not handled
        raise Exception('Not SGTIN-96.')

    binary = "{0:020b}".format(int(sgtin_96, 16)).zfill(96)

    header = int(binary[:8], 2)
    tag_filter = int(binary[8:11], 2)

    partition = binary[11:14]
    partition_value = int(partition, 2)

    m, l, n, k = PARTITION_MAP[partition_value]

    company_start = 8 + 3 + 3
    company_end = company_start + m
    company_data = int(binary[company_start:company_end], 2)
    if company_data > pow(10, l):
        # can't be too large
        raise Exception('Company value is too large')
    company_prefix = str(company_data).zfill(l)

    item_start = company_end
    item_end = item_start + n
    item_data = binary[item_start:item_end]
    item_number = int(item_data, 2)
    item_reference = str(item_number).zfill(k)

    serial = int(binary[-38:], 2)

    URI = "urn:epc:tag:sgtin-96:{F}.{C}.{I}.{S}".format(F=tag_filter,
                                                        C=company_prefix,
                                                        I=item_reference,
                                                        S=serial)

    return {
        "header": header,
        "filter": tag_filter,
        "partition": partition,
        "company_prefix": company_prefix,
        "item_reference": item_reference,
        "serial": serial
    }, URI