<?php
/**
 * PHP Class for handling Google Authenticator 2-factor authentication
 *
 * @author Michael Kliewe
 * @copyright 2012 Michael Kliewe
 * @license http://www.opensource.org/licenses/bsd-license.php BSD License
 * @link http://www.phpgangsta.de/
 *
 * small adjustments by matomo.org
 * - renamed class
 * - removed method getQRCodeGoogleUrl
 * - use better random secret generator
 * - apply proper type hints
 */

class TwoFactorAuthenticator
{
    protected $_codeLength = 6;

    /**
     * Create new secret.
     * 16 characters, randomly chosen from the allowed base32 characters.
     *
     * @param int $secretLength
     * @return string
     */
    public function createSecret(int $secretLength = 16): string
    {
        $validChars = $this->_getBase32LookupTable();
        unset($validChars[32]);

        // modified by matomo.org
        return \Piwik\Common::getRandomString($secretLength, implode('', $validChars));
    }

    /**
     * Calculate the code, with given secret and point in time
     *
     * @param string $secret
     * @param int|null $timeSlice
     * @return string
     */
    public function getCode(string $secret, ?int $timeSlice = null)
    {
        if ($timeSlice === null) {
            $timeSlice = floor(time() / 30);
        }

        $secretkey = $this->_base32Decode($secret);

        // Pack time into binary string
        $time = chr(0).chr(0).chr(0).chr(0).pack('N*', $timeSlice);
        // Hash it with users secret key
        $hm = hash_hmac('SHA1', $time, $secretkey, true);
        // Use last nipple of result as index/offset
        $offset = ord(substr($hm, -1)) & 0x0F;
        // grab 4 bytes of the result
        $hashpart = substr($hm, $offset, 4);

        // Unpak binary value
        $value = unpack('N', $hashpart);
        $value = $value[1];
        // Only 32 bits
        $value = $value & 0x7FFFFFFF;

        $modulo = pow(10, $this->_codeLength);
        return str_pad($value % $modulo, $this->_codeLength, '0', STR_PAD_LEFT);
    }

    /**
     * Check if the code is correct. This will accept codes starting from $discrepancy*30sec ago to $discrepancy*30sec from now
     *
     * @param string $secret
     * @param string $code
     * @param int $discrepancy This is the allowed time drift in 30 second units (8 means 4 minutes before or after)
     * @param int|null $currentTimeSlice time slice if we want use other that time()
     * @return bool
     */
    public function verifyCode(string $secret, string $code, int $discrepancy = 1, ?int $currentTimeSlice = null): bool
    {
        if ($currentTimeSlice === null) {
            $currentTimeSlice = floor(time() / 30);
        }

        for ($i = -$discrepancy; $i <= $discrepancy; $i++) {
            $calculatedCode = $this->getCode($secret, $currentTimeSlice + $i);
            if ($this->timingSafeEquals($calculatedCode, $code)) {
                return true;
            }
        }

        return false;
    }

    /**
     * Set the code length, should be >=6
     *
     * @param int $length
     * @return self
     */
    public function setCodeLength(int $length)
    {
        $this->_codeLength = $length;
        return $this;
    }

    /**
     * Helper class to decode base32
     *
     * @param string $secret
     * @return string
     */
    protected function _base32Decode(string $secret): string
    {
        if (empty($secret)) return '';

        $base32chars = $this->_getBase32LookupTable();
        $base32charsFlipped = array_flip($base32chars);

        $paddingCharCount = substr_count($secret, $base32chars[32]);
        $allowedValues = array(6, 4, 3, 1, 0);
        if (!in_array($paddingCharCount, $allowedValues)) return false;
        for ($i = 0; $i < 4; $i++){
            if ($paddingCharCount == $allowedValues[$i] &&
                substr($secret, -($allowedValues[$i])) != str_repeat($base32chars[32], $allowedValues[$i])) return false;
        }
        $secret = str_replace('=','', $secret);
        $secret = str_split($secret);
        $binaryString = "";
        for ($i = 0; $i < count($secret); $i = $i+8) {
            $x = "";
            if (!in_array($secret[$i], $base32chars)) return false;
            for ($j = 0; $j < 8; $j++) {
                $x .= str_pad(base_convert($base32charsFlipped[@$secret[$i + $j]] ?? '', 10, 2), 5, '0', STR_PAD_LEFT);
            }
            $eightBits = str_split($x, 8);
            for ($z = 0; $z < count($eightBits); $z++) {
                $binaryString .= ( ($y = chr(base_convert($eightBits[$z], 2, 10))) || ord($y) == 48 ) ? $y:"";
            }
        }
        return $binaryString;
    }

    /**
     * Helper class to encode base32
     *
     * @param string $secret
     * @param bool $padding
     * @return string
     */
    protected function _base32Encode(string $secret, bool $padding = true): string
    {
        if (empty($secret)) return '';

        $base32chars = $this->_getBase32LookupTable();

        $secret = str_split($secret);
        $binaryString = "";
        for ($i = 0; $i < count($secret); $i++) {
            $binaryString .= str_pad(base_convert(ord($secret[$i]), 10, 2), 8, '0', STR_PAD_LEFT);
        }
        $fiveBitBinaryArray = str_split($binaryString, 5);
        $base32 = "";
        $i = 0;
        while ($i < count($fiveBitBinaryArray)) {
            $base32 .= $base32chars[base_convert(str_pad($fiveBitBinaryArray[$i], 5, '0'), 2, 10)];
            $i++;
        }
        if ($padding && ($x = strlen($binaryString) % 40) != 0) {
            if ($x == 8) $base32 .= str_repeat($base32chars[32], 6);
            elseif ($x == 16) $base32 .= str_repeat($base32chars[32], 4);
            elseif ($x == 24) $base32 .= str_repeat($base32chars[32], 3);
            elseif ($x == 32) $base32 .= $base32chars[32];
        }
        return $base32;
    }

    /**
     * Get array with all 32 characters for decoding from/encoding to base32
     *
     * @return array<string>
     */
    protected function _getBase32LookupTable(): array
    {
        return array(
            'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', //  7
            'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', // 15
            'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', // 23
            'Y', 'Z', '2', '3', '4', '5', '6', '7', // 31
            '='  // padding char
        );
    }

    /**
     * A timing safe equals comparison
     * more info here: https://blog.ircmaxell.com/2014/11/its-all-about-time.html.
     *
     * @param string $safeString The internal (safe) value to be checked
     * @param string $userString The user submitted (unsafe) value
     *
     * @return bool True if the two strings are identical
     */
    private function timingSafeEquals(string $safeString, string $userString): bool
    {
        if (function_exists('hash_equals')) {
            return hash_equals($safeString, $userString);
        }
        $safeLen = strlen($safeString);
        $userLen = strlen($userString);

        if ($userLen != $safeLen) {
            return false;
        }

        $result = 0;

        for ($i = 0; $i < $userLen; ++$i) {
            $result |= (ord($safeString[$i]) ^ ord($userString[$i]));
        }

        // They are only identical strings if $result is exactly 0...
        return $result === 0;
    }
}
