<?php

namespace RobThree\Auth;

use RobThree\Auth\Providers\Qr\IQRCodeProvider;
use RobThree\Auth\Providers\Qr\QRServerProvider;
use RobThree\Auth\Providers\Rng\CSRNGProvider;
use RobThree\Auth\Providers\Rng\HashRNGProvider;
use RobThree\Auth\Providers\Rng\IRNGProvider;
use RobThree\Auth\Providers\Rng\MCryptRNGProvider;
use RobThree\Auth\Providers\Rng\OpenSSLRNGProvider;
use RobThree\Auth\Providers\Time\HttpTimeProvider;
use RobThree\Auth\Providers\Time\ITimeProvider;
use RobThree\Auth\Providers\Time\LocalMachineTimeProvider;
use RobThree\Auth\Providers\Time\NTPTimeProvider;

// Based on / inspired by: https://github.com/PHPGangsta/GoogleAuthenticator
// Algorithms, digits, period etc. explained: https://github.com/google/google-authenticator/wiki/Key-Uri-Format
class TwoFactorAuth {
	/** @var string */
	private $algorithm;

	/** @var int */
	private $period;

	/** @var int */
	private $digits;

	/** @var string */
	private $issuer;

	/** @var ?IQRCodeProvider */
	private $qrcodeprovider = null;

	/** @var ?IRNGProvider */
	private $rngprovider = null;

	/** @var ?ITimeProvider */
	private $timeprovider = null;

	/** @var string */
	private static $_base32dict = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567=";

	/** @var array */
	private static $_base32;

	/** @var array */
	private static $_base32lookup = [];

	/** @var array */
	private static $_supportedalgos = ["sha1", "sha256", "sha512", "md5"];

	/**
	 * @param ?string $issuer
	 * @param int $digits
	 * @param int $period
	 * @param string $algorithm
	 * @param ?IQRCodeProvider $qrcodeprovider
	 * @param ?IRNGProvider $rngprovider
	 * @param ?ITimeProvider $timeprovider
	 */
	public function __construct(
		$issuer = null,
		$digits = 6,
		$period = 30,
		$algorithm = "sha1",
		IQRCodeProvider $qrcodeprovider = null,
		IRNGProvider $rngprovider = null,
		ITimeProvider $timeprovider = null,
	) {
		$this->issuer = $issuer;
		if (!is_int($digits) || $digits <= 0) {
			throw new TwoFactorAuthException("Digits must be int > 0");
		}
		$this->digits = $digits;

		if (!is_int($period) || $period <= 0) {
			throw new TwoFactorAuthException("Period must be int > 0");
		}
		$this->period = $period;

		$algorithm = strtolower(trim($algorithm));
		if (!in_array($algorithm, self::$_supportedalgos)) {
			throw new TwoFactorAuthException("Unsupported algorithm: " . $algorithm);
		}
		$this->algorithm = $algorithm;
		$this->qrcodeprovider = $qrcodeprovider;
		$this->rngprovider = $rngprovider;
		$this->timeprovider = $timeprovider;

		self::$_base32 = str_split(self::$_base32dict);
		self::$_base32lookup = array_flip(self::$_base32);
	}

	/**
	 * Create a new secret
	 *
	 * @param int $bits
	 * @param bool $requirecryptosecure
	 *
	 * @return string
	 */
	public function createSecret($bits = 80, $requirecryptosecure = true) {
		$secret = "";
		$bytes = (int) ceil($bits / 5); //We use 5 bits of each byte (since we have a 32-character 'alphabet' / BASE32)
		$rngprovider = $this->getRngProvider();
		if ($requirecryptosecure && !$rngprovider->isCryptographicallySecure()) {
			throw new TwoFactorAuthException("RNG provider is not cryptographically secure");
		}
		$rnd = $rngprovider->getRandomBytes($bytes);
		for ($i = 0; $i < $bytes; $i++) {
			$secret .= self::$_base32[ord($rnd[$i]) & 31]; //Mask out left 3 bits for 0-31 values
		}
		return $secret;
	}

	/**
	 * Calculate the code with given secret and point in time
	 *
	 * @param string $secret
	 * @param ?int $time
	 *
	 * @return string
	 */
	public function getCode($secret, $time = null) {
		$secretkey = $this->base32Decode($secret);

		$timestamp = "\0\0\0\0" . pack("N*", $this->getTimeSlice($this->getTime($time))); // Pack time into binary string
		$hashhmac = hash_hmac($this->algorithm, $timestamp, $secretkey, true); // Hash it with users secret key
		$hashpart = substr($hashhmac, ord(substr($hashhmac, -1)) & 0x0f, 4); // Use last nibble of result as index/offset and grab 4 bytes of the result
		$value = unpack("N", $hashpart); // Unpack binary value
		$value = $value[1] & 0x7fffffff; // Drop MSB, keep only 31 bits

		return str_pad(
			(string) ($value % pow(10, $this->digits)),
			$this->digits,
			"0",
			STR_PAD_LEFT,
		);
	}

	/**
	 * Check if the code is correct. This will accept codes starting from ($discrepancy * $period) sec ago to ($discrepancy * period) sec from now
	 *
	 * @param string $secret
	 * @param string $code
	 * @param int $discrepancy
	 * @param ?int $time
	 * @param int $timeslice
	 *
	 * @return bool
	 */
	public function verifyCode($secret, $code, $discrepancy = 1, $time = null, &$timeslice = 0) {
		$timestamp = $this->getTime($time);

		$timeslice = 0;

		// To keep safe from timing-attacks we iterate *all* possible codes even though we already may have
		// verified a code is correct. We use the timeslice variable to hold either 0 (no match) or the timeslice
		// of the match. Each iteration we either set the timeslice variable to the timeslice of the match
		// or set the value to itself.  This is an effort to maintain constant execution time for the code.
		for ($i = -$discrepancy; $i <= $discrepancy; $i++) {
			$ts = $timestamp + $i * $this->period;
			$slice = $this->getTimeSlice($ts);
			$timeslice = $this->codeEquals($this->getCode($secret, $ts), $code)
				? $slice
				: $timeslice;
		}

		return $timeslice > 0;
	}

	/**
	 * Timing-attack safe comparison of 2 codes (see http://blog.ircmaxell.com/2014/11/its-all-about-time.html)
	 *
	 * @param string $safe
	 * @param string $user
	 *
	 * @return bool
	 */
	private function codeEquals($safe, $user) {
		if (function_exists("hash_equals")) {
			return hash_equals($safe, $user);
		}
		// In general, it's not possible to prevent length leaks. So it's OK to leak the length. The important part is that
		// we don't leak information about the difference of the two strings.
		if (strlen($safe) === strlen($user)) {
			$result = 0;
			for ($i = 0; $i < strlen($safe); $i++) {
				$result |= ord($safe[$i]) ^ ord($user[$i]);
			}
			return $result === 0;
		}
		return false;
	}

	/**
	 * Get data-uri of QRCode
	 *
	 * @param string $label
	 * @param string $secret
	 * @param mixed $size
	 *
	 * @return string
	 */
	public function getQRCodeImageAsDataUri($label, $secret, $size = 200) {
		if (!is_int($size) || $size <= 0) {
			throw new TwoFactorAuthException("Size must be int > 0");
		}

		$qrcodeprovider = $this->getQrCodeProvider();
		return "data:" .
			$qrcodeprovider->getMimeType() .
			";base64," .
			base64_encode(
				$qrcodeprovider->getQRCodeImage($this->getQRText($label, $secret), $size),
			);
	}

	/**
	 * Compare default timeprovider with specified timeproviders and ensure the time is within the specified number of seconds (leniency)
	 * @param ?array $timeproviders
	 * @param int $leniency
	 *
	 * @return void
	 */
	public function ensureCorrectTime(array $timeproviders = null, $leniency = 5) {
		if ($timeproviders === null) {
			$timeproviders = [new NTPTimeProvider(), new HttpTimeProvider()];
		}

		// Get default time provider
		$timeprovider = $this->getTimeProvider();

		// Iterate specified time providers
		foreach ($timeproviders as $t) {
			if (!($t instanceof ITimeProvider)) {
				throw new TwoFactorAuthException("Object does not implement ITimeProvider");
			}

			// Get time from default time provider and compare to specific time provider and throw if time difference is more than specified number of seconds leniency
			if (abs($timeprovider->getTime() - $t->getTime()) > $leniency) {
				throw new TwoFactorAuthException(
					sprintf(
						"Time for timeprovider is off by more than %d seconds when compared to %s",
						$leniency,
						get_class($t),
					),
				);
			}
		}
	}

	/**
	 * @param ?int $time
	 *
	 * @return int
	 */
	private function getTime($time = null) {
		return $time === null ? $this->getTimeProvider()->getTime() : $time;
	}

	/**
	 * @param int $time
	 * @param int $offset
	 *
	 * @return int
	 */
	private function getTimeSlice($time = null, $offset = 0) {
		return (int) floor($time / $this->period) + $offset * $this->period;
	}

	/**
	 * Builds a string to be encoded in a QR code
	 *
	 * @param string $label
	 * @param string $secret
	 *
	 * @return string
	 */
	public function getQRText($label, $secret) {
		return "otpauth://totp/" .
			rawurlencode($label) .
			"?secret=" .
			rawurlencode($secret) .
			"&issuer=" .
			rawurlencode((string) $this->issuer) .
			"&period=" .
			intval($this->period) .
			"&algorithm=" .
			rawurlencode(strtoupper($this->algorithm)) .
			"&digits=" .
			intval($this->digits);
	}

	/**
	 * @param string $value
	 * @return string
	 */
	private function base32Decode($value) {
		if (strlen($value) == 0) {
			return "";
		}

		if (preg_match("/[^" . preg_quote(self::$_base32dict) . "]/", $value) !== 0) {
			throw new TwoFactorAuthException("Invalid base32 string");
		}

		$buffer = "";
		foreach (str_split($value) as $char) {
			if ($char !== "=") {
				$buffer .= str_pad(decbin(self::$_base32lookup[$char]), 5, "0", STR_PAD_LEFT);
			}
		}
		$length = strlen($buffer);
		$blocks = trim(chunk_split(substr($buffer, 0, $length - ($length % 8)), 8, " "));

		$output = "";
		foreach (explode(" ", $blocks) as $block) {
			$output .= chr(bindec(str_pad($block, 8, "0", STR_PAD_RIGHT)));
		}
		return $output;
	}

	/**
	 * @return IQRCodeProvider
	 * @throws TwoFactorAuthException
	 */
	public function getQrCodeProvider() {
		// Set default QR Code provider if none was specified
		if (null === $this->qrcodeprovider) {
			return $this->qrcodeprovider = new QRServerProvider();
		}
		return $this->qrcodeprovider;
	}

	/**
	 * @return IRNGProvider
	 * @throws TwoFactorAuthException
	 */
	public function getRngProvider() {
		if (null !== $this->rngprovider) {
			return $this->rngprovider;
		}
		if (function_exists("random_bytes")) {
			return $this->rngprovider = new CSRNGProvider();
		}
		if (function_exists("mcrypt_create_iv")) {
			return $this->rngprovider = new MCryptRNGProvider();
		}
		if (function_exists("openssl_random_pseudo_bytes")) {
			return $this->rngprovider = new OpenSSLRNGProvider();
		}
		if (function_exists("hash")) {
			return $this->rngprovider = new HashRNGProvider();
		}
		throw new TwoFactorAuthException("Unable to find a suited RNGProvider");
	}

	/**
	 * @return ITimeProvider
	 * @throws TwoFactorAuthException
	 */
	public function getTimeProvider() {
		// Set default time provider if none was specified
		if (null === $this->timeprovider) {
			return $this->timeprovider = new LocalMachineTimeProvider();
		}
		return $this->timeprovider;
	}
}