local base64 = require "util.encodings".base64;

local hmac = require "openssl.hmac";

local luatz = require "luatz";

local otp = require "otp";

local DIGEST_TYPE = "SHA256";

local OTP_DEVIATION = 1;

local OTP_DIGITS = 8;

local OTP_INTERVAL = 30;

local nonce_cache = {};

local function check_nonce(jid, otp_value, nonce)

	-- We cache all nonces used per OTP, to ensure that a token cannot be used

	-- more than once.

	--

	-- We assume that the OTP is valid in the current time window. This is the

	-- case because we only call check_nonce *after* the OTP has been verified.

	--

	-- We only store one OTP per JID, so if a new OTP comes in, we wipe the

	-- previous OTP and its cached nonces.

	if nonce_cache[jid] == nil or nonce_cache[jid][otp_value] == nil then

		nonce_cache[jid] = {}

		nonce_cache[jid][otp_value] = {}

		nonce_cache[jid][otp_value][nonce] = true

		return true;

	end

	if nonce_cache[jid][otp_value][nonce] == true then

		return false;

	else

		nonce_cache[jid][otp_value][nonce] = true;

		return true;

	end

end

local function verify_token(username, password, otp_seed, token_secret, log)

	local totp = otp.new_totp_from_key(otp_seed, OTP_DIGITS, OTP_INTERVAL)

	local token = string.match(password, "(%d+) ")

	local otp_value = token:sub(1,8)

	local nonce = token:sub(9)

	local signature = base64.decode(string.match(password, " (.+)"))

	local jid = username.."@"..module.host

	if totp:verify(otp_value, OTP_DEVIATION, luatz.time()) then

		log("debug", "The TOTP was verified");

		local hmac_ctx = hmac.new(token_secret, DIGEST_TYPE)

		if signature == hmac_ctx:final(otp_value..nonce..jid) then

			log("debug", "The key was verified");

			if check_nonce(jid, otp_value, nonce) then

				log("debug", "The nonce was verified");

				return true;

			end

		end

	end

	log("debug", "Verification failed");

	return false;

end

return {

	OTP_DEVIATION = OTP_DIGITS,

	OTP_DIGITS = OTP_DIGITS,

	OTP_INTERVAL = OTP_INTERVAL,

	DIGEST_TYPE = DIGEST_TYPE,

	verify_token = verify_token;

}