index.js

const { createHmac } = require("crypto");
const { existsSync, readFileSync } = require("fs");
const { exit } = require("process");

const clipboardy = require("clipboardy");
const base32Decode = require("base32-decode");
const ntpClient = require("ntp-client");

(async () => {
	let errorMessage = null;
	let secret = null;
	if (existsSync("secret.raw")) {
		secret = readFileSync("secret.raw");
		if (secret.length !== 20) {
			errorMessage = "Secret key should be 20 bytes!";
		}
	} else if (existsSync("secret.base64")) {
		const base64String = readFileSync("secret.base64", "utf8").trim();
		if (/^[A-Za-z0-9+/]{27}=?$/.test(base64String)) {
			secret = Buffer.from(base64String, "base64");
		} else {
			errorMessage = "Secret key should be 27 base-64 digits!";
		}
	} else if (existsSync("secret.base32")) {
		const base32String = readFileSync("secret.base32", "utf8").trim();
		if (/^[A-Za-z2-7]{32}$/.test(base32String)) {
			secret = Buffer.from(base32Decode(base32String, "RFC4648"));
		} else {
			errorMessage = "Secret key should be 32 base-32 digits!";
		}
	} else if (existsSync("secret.hex")) {
		const hexString = readFileSync("secret.hex", "utf8").trim();
		if (/^[0-9a-fA-F]{40}$/.test(hexString)) {
			secret = Buffer.from(hexString, "hex");
		} else {
			errorMessage = "Secret key should be 40 hex digits!";
		}
	} else {
		errorMessage =
			"Please create a 'secret' file (secret.hex OR secret.base32 OR secret.raw)";
	}

	if (errorMessage) {
		console.error(errorMessage);
		setTimeout(() => exit(1), 5000);
	} else {
		// initialize hmac of secret key
		const hmac = createHmac("sha1", secret);

		// get current time
		let time = new Date();
		try {
			time = await new Promise((resolve, reject) =>
				ntpClient.getNetworkTime("pool.ntp.org", 123, (err, date) =>
					err ? reject(err) : resolve(date)
				)
			);
			console.log("Set time via ntp.org");
		} catch (e1) {
			console.error("Error fetching time via ntp.org:", e1);
			try {
				const response = await fetch("https://www.google.com/");
				time = new Date(response.headers.get("date"));
				console.log("Set time via google.com");
			} catch (e2) {
				console.error("Error fetching time via google.com:", e2);
				setTimeout(() => exit(1), 5000);
			}
		}

		// calculate number of 30-second intervals since 1970-01-01
		const c = Buffer.alloc(8);
		c.writeBigInt64BE(BigInt(time.getTime()) / 30000n);

		// digest the payload
		hmac.update(c);

		// get hmac output
		const buf = hmac.digest();

		// the offset is the last 4 bits of the output
		const offset = buf.readUInt8(19) & 0xf;

		// get the integer result
		const n = buf.readUInt32BE(offset) & 0x7fffffff;

		// get the last 6 digits of integer result
		const sixDigits = (n % 1000000).toString().padStart(6, "0");

		// copy to clipboard
		clipboardy.writeSync(sixDigits);
	}
})();