import { getById, h } from "/common.module.js";

function writeInfo(label, msg) {
    log.appendChild(
        h("div",
            [h("div", {class: "info"}, [h("span", {class: "noselect"}, label), h("span", msg)])]
        ),
    );
}

export function onLoad() {
    const gen_bsn = getById("bsn");
    gen_bsn.addEventListener("click", generateBsn);

    const gen_iban = getById("iban");
    gen_iban.addEventListener("click", generateIban);
}

function generateBsn() {
    const nr9 = Math.floor(Math.random() * 7);
    const nr8 = Math.floor(Math.random() * 10);
    const nr7 = Math.floor(Math.random() * 10);
    const nr6 = Math.floor(Math.random() * 10);
    const nr5 = Math.floor(Math.random() * 10);
    const nr4 = Math.floor(Math.random() * 10);
    const nr3 = Math.floor(Math.random() * 10);
    let nr2 = Math.floor(Math.random() * 10);
    const bsnNumber =
        9 * nr9 +
        8 * nr8 +
        7 * nr7 +
        6 * nr6 +
        5 * nr5 +
        4 * nr4 +
        3 * nr3 +
        2 * nr2;
    let nr1 = Math.floor(bsnNumber - Math.floor(bsnNumber / 11) * 11);
    if (nr1 > 9) {
        if (nr2 > 0) {
            nr2 -= 1;
            nr1 = 8;
        } else {
            nr2 += 1;
            nr1 = 1;
        }
    }

    const BSNString = "" + nr9 + nr8 + nr7 + nr6 + nr5 + nr4 + nr3 + nr2 + nr1;
    writeInfo("BSN: ", BSNString);
}

// Bank identifiers of a few Dutch banks, as they appear in an IBAN.
const BANK_CODES = ["ABNA", "ASNB", "BUNQ", "INGB", "KNAB", "RABO", "RBRB", "SNSB", "TRIO"];

/** @param {number} count @returns {string} */
function randomDigits(count) {
    let digits = "";
    for (let i = 0; i < count; i++) {
        digits += Math.floor(Math.random() * 10);
    }
    return digits;
}

/**
 * An old-style Dutch account number: 9 digits that pass the "elfproef", where
 * the digits weighted 9, 8, ... 1 add up to a multiple of 11. IBANs pad those
 * to 10 digits with a leading zero.
 * @returns {string}
 */
function randomAccountNumber() {
    while (true) {
        const digits = randomDigits(8);
        let sum = 0;
        for (let i = 0; i < 8; i++) {
            sum += (9 - i) * Number(digits[i]);
        }
        // The ninth digit weighs 1, so it has to make up the rest on its own.
        const last = (11 - (sum % 11)) % 11;
        if (last < 10) {
            return "0" + digits + last;
        }
        // It would have to be a 10 to balance out; draw eight new digits.
    }
}

/**
 * Letters count as A=10 .. Z=35 in the ISO 7064 MOD 97-10 check.
 * @param {string} letters
 * @returns {string}
 */
function lettersToDigits(letters) {
    return [...letters].map((c) => c.charCodeAt(0) - 55).join("");
}

/**
 * Remainder of a number too large for a JS number, taken digit by digit.
 * @param {string} digits
 * @returns {number}
 */
function mod97(digits) {
    let rest = 0;
    for (const digit of digits) {
        rest = (rest * 10 + Number(digit)) % 97;
    }
    return rest;
}

function generateIban() {
    const bank = BANK_CODES[Math.floor(Math.random() * BANK_CODES.length)];
    const account = randomAccountNumber();
    // ISO 13616: move "NL" + the check digits to the back, then pick the check
    // digits that make the whole thing leave a remainder of 1 modulo 97.
    const rest = mod97(lettersToDigits(bank) + account + lettersToDigits("NL") + "00");
    const check = String(98 - rest).padStart(2, "0");

    writeInfo("IBAN: ", "NL" + check + bank + account);
}