Create reference numbers for invoicing. International or local (Finnish) RF format

createReferenceNumbers.ts

export const createReferenceNumbers = (
    baseStr: string = "000",
    qty = 10,
    international = false
): string[] => {
    const baseNumber = BigInt(baseStr);
  
    return Array.from({ length: qty }, (_value, idx) => {
        const base = String(baseNumber + BigInt(idx));
        const checksum: number =
            10 -
            (Array.from(base).reduceRight(
                (acc: number, current: string, idx, arr) => {
                    return (
                        acc +
                        Number.parseInt(current) *
                            prodCoefficients[
                                (arr.length - 1 - idx) % lenOfCoefficients
                            ]
                    );
                },
                0
            ) %
                10);
  
        const finnishRefNumber = `${base}${checksum === 10 ? 0 : checksum}`;
  
        if (international) {
            const internationalChecksum = String(
                98n - (BigInt(finnishRefNumber + rfSequence) % 97n)
            ).padStart(2, "0");
            return `RF${internationalChecksum}${finnishRefNumber}`;
        } else {
            return finnishRefNumber;
        }
    });
};