/**
 * luhn.js
 *
 */

import {terminal} from "./dfhi.js";

const checkLuhnNumber = (n) => {
    let sumEvent = 0n;
    let sumOdd = 0n;
    while(n > 0) {
        sumOdd += (n % 10n);  // modulo division base 10 to get the last digit
        n = n/10n;            // integer division base 10 to shift credit number one digit to right
        let rest = n % 10n;   // get the second-last digit
        let p = rest*2n;
        sumEvent += (p > 9n) ? (p - 9n) : p;
        n = n/10n;
    }
    return (sumEvent + sumOdd) % 10n;
}

window.main = (...argv) => {
    try {
        let credit = argv[0];
        let n = BigInt(credit.replace(/[-_\s+]/g, ''));
        const sum = checkLuhnNumber(n);
        if (sum === 0n) {
            terminal.printl(`${credit} may be a valid credit number`);
        } else {
            terminal.printl(`${credit} is not a valid credit number`);
        }
    }catch (e) {
        terminal.printl("Die eingegebene Zeichenkette ist keine Credit Nummer");
        terminal.printl("Erlaubten Zeichen sind Ziffer, Leerzeichen und Bindenstrich");
    }
};