Code128 Checksum

code128.php

<?php

const START = 'Ë';
const END = 'û';
const MOD = 103;
const OFFSET = 32;
const SPECIAL_OFFSET = 68;
const PACKAGE = '06';

function calcChecksum($value)
{
    $digits = str_split($value);

    $sum = array_reduce(
        array_map(
            function ($digit, $index) {
                return (mb_ord($digit) - OFFSET) * ($index + 1);
            },
            $digits,
            array_keys($digits)
        ),
        function ($carry, $item) {
            return $carry + $item;
        },
        MOD
    );

    if (($sum % MOD) + OFFSET > 126) {
        return mb_chr(($sum % MOD) + OFFSET + SPECIAL_OFFSET);
    }

    return mb_chr(($sum % MOD) + OFFSET);
}

$file = fopen('/Users/maze/Downloads/bst1.csv', 'r');

while (($data = fgetcsv($file, 0, '|')) !== false) {
    $id = PACKAGE . $data[2];
    $checksum = calcChecksum($id);

    echo $barcode = $id . '|' . START . $id . $checksum . END . PHP_EOL;
}