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/**
* Checks that the given string passes the luhn algorithm.
*
* @param str The string to validate.
*/
export function luhnCheck(str: string): boolean {
return luhnChecksum(str) === 0;
}
/**
* Calculates the luhn check value for the given string.
*
* @param str The string to calculate the check value for.
* May contain the `L` placeholder at the end.
*/
export function luhnCheckValue(str: string): number {
const checksum = luhnChecksum(str.replace(/L?$/, '0'));
return checksum === 0 ? 0 : 10 - checksum;
}
/**
* Calculates the luhn checksum value for the given value.
*
* @param str The string to generate the checksum for.
*/
function luhnChecksum(str: string): number {
str = str.replaceAll(/[\s-]/g, '');
let sum = 0;
let alternate = false;
for (let i = str.length - 1; i >= 0; i--) {
let n = Number.parseInt(str[i]);
if (alternate) {
n *= 2;
if (n > 9) {
n = (n % 10) + 1;
}
}
sum += n;
alternate = !alternate;
}
return sum % 10;
}
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