const CHARS = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789';
const PHONETIC = ['Alpha', 'Bravo', 'Charlie', 'Delta', 'Echo', 'Foxtrot', 'Golf', 'Hotel',
	'India', 'Juliet', 'Kilo', 'Lima', 'Mike', 'November', 'Oscar', 'Papa', 'Quebec', 'Romeo',
	'Sierra', 'Tango', 'Uniform', 'Victor', 'Whiskey', 'Xray', 'Yankee', 'Zulu'];

class SeededRandom {
	constructor(seed) {
		this.seed = seed;
		this.counter = 0;
	}

	next() {
		const hash = CryptoJS.SHA256(this.seed + ':' + this.counter);
		this.counter++;
		const hex = hash.toString(CryptoJS.enc.Hex);
		return parseInt(hex.substring(0, 8), 16) / 0xFFFFFFFF;
	}

	nextInt(min, max) {
		return Math.floor(this.next() * (max - min)) + min;
	}

	choice(arr) {
		return arr[this.nextInt(0, arr.length)];
	}
}

function generateHOTP(secret, nonce) {
	const rng = new SeededRandom(secret + ':hotp:' + nonce);
	let code = '';
	for (let i = 0; i < 2; i++) {
		code += rng.choice(CHARS.split(''));
	}
	return code;
}

function generateAuthTable(seed, tableIndex) {
	const rng = new SeededRandom(seed + ':table:' + tableIndex);
	const rows = 'NOPQRSTUVWXYZ'.split('');
	const cols = 'ABCDEFGHIJKLM'.split('');

	const table = [];
	for (let row of rows) {
		const rowData = [];
		for (let col of cols) {
			rowData.push(rng.choice(CHARS.split('')));
		}
		table.push(rowData);
	}

	return table;
}

function generatePad(seed, padKey, length = 60) {
	const rng = new SeededRandom(seed + ':pad:' + padKey);
	const pad = [];
	for (let i = 0; i < length; i++) {
		pad.push(rng.nextInt(0, 1000));
	}
	return pad;
}

function generatePadDisplay(seed, padKey) {
	const rng = new SeededRandom(seed + ':pad:' + padKey);
	const groups = [];
	for (let i = 0; i < 24; i++) {
		const num = rng.nextInt(0, 1000).toString().padStart(3, '0');
		groups.push(num);
	}
	return groups.join(' ');
}

function encodeMessage(message, key, padKey, useStream = true) {
	const messageBytes = new TextEncoder().encode(message);
	const padLength = useStream ? messageBytes.length : 60;
	const pad = generatePad(key, padKey, padLength);
	const encoded = [];
	for (let i = 0; i < messageBytes.length; i++) {
		const padValue = pad[i % pad.length];
		const result = (messageBytes[i] + padValue) % 1000;
		encoded.push(result.toString().padStart(3, '0'));
	}
	return encoded.join('');
}

function decodeMessage(encoded, key, padKey, useStream = true) {
	const values = [];
	for (let i = 0; i < encoded.length; i += 3) {
		values.push(parseInt(encoded.substr(i, 3), 10));
	}
	const padLength = useStream ? values.length : 60;
	const pad = generatePad(key, padKey, padLength);
	const decoded = [];
	for (let i = 0; i < values.length; i++) {
		const padValue = pad[i % pad.length];
		let result = (values[i] - padValue) % 1000;
		if (result < 0) result += 1000;
		decoded.push(result);
	}
	return new TextDecoder().decode(new Uint8Array(decoded));
}