<?php

namespace NSLPro\JWT;

use DateTime;
use DomainException;
use InvalidArgumentException;
use UnexpectedValueException;

/**
 * JSON Web Token implementation, based on this spec:
 * https://tools.ietf.org/html/rfc7519
 *
 * PHP version 5
 *
 * @category Authentication
 * @package  Authentication_JWT
 * @author   Neuman Vong <neuman@twilio.com>
 * @author   Anant Narayanan <anant@php.net>
 * @license  http://opensource.org/licenses/BSD-3-Clause 3-clause BSD
 * @link     https://github.com/firebase/php-jwt
 */
class JWT {

    const ASN1_INTEGER = 0x02;
    const ASN1_SEQUENCE = 0x10;
    const ASN1_BIT_STRING = 0x03;

    /**
     * When checking nbf, iat or expiration times,
     * we want to provide some extra leeway time to
     * account for clock skew.
     */
    public static $leeway = 0;

    /**
     * Allow the current timestamp to be specified.
     * Useful for fixing a value within unit testing.
     *
     * Will default to PHP time() value if null.
     */
    public static $timestamp = null;

    public static $supported_algs = array(
        'ES256' => array(
            'openssl',
            'SHA256'
        ),
        'HS256' => array(
            'hash_hmac',
            'SHA256'
        ),
        'HS384' => array(
            'hash_hmac',
            'SHA384'
        ),
        'HS512' => array(
            'hash_hmac',
            'SHA512'
        ),
        'RS256' => array(
            'openssl',
            'SHA256'
        ),
        'RS384' => array(
            'openssl',
            'SHA384'
        ),
        'RS512' => array(
            'openssl',
            'SHA512'
        ),
    );

    /**
     * Decodes a JWT string into a PHP object.
     *
     * @param string                $jwt                The JWT
     * @param string|array|resource $key                The key, or map of keys.
     *                                                  If the algorithm used is asymmetric, this is the public key
     * @param array                 $allowed_algs       List of supported verification algorithms
     *                                                  Supported algorithms are 'ES256', 'HS256', 'HS384', 'HS512',
     *                                                  'RS256', 'RS384', and 'RS512'
     *
     * @return object The JWT's payload as a PHP object
     *
     * @throws UnexpectedValueException     Provided JWT was invalid
     * @throws SignatureInvalidException    Provided JWT was invalid because the signature verification failed
     * @throws BeforeValidException         Provided JWT is trying to be used before it's eligible as defined by 'nbf'
     * @throws BeforeValidException         Provided JWT is trying to be used before it's been created as defined by
     *                                      'iat'
     * @throws ExpiredException             Provided JWT has since expired, as defined by the 'exp' claim
     *
     * @uses jsonDecode
     * @uses urlsafeB64Decode
     */
    public static function decode($jwt, $key, array $allowed_algs = array()) {
        $timestamp = is_null(static::$timestamp) ? time() : static::$timestamp;

        if (empty($key)) {
            throw new InvalidArgumentException('Key may not be empty');
        }
        $tks = explode('.', $jwt);
        if (count($tks) != 3) {
            throw new UnexpectedValueException('Wrong number of segments');
        }
        list($headb64, $bodyb64, $cryptob64) = $tks;
        if (null === ($header = static::jsonDecode(static::urlsafeB64Decode($headb64)))) {
            throw new UnexpectedValueException('Invalid header encoding');
        }
        if (null === $payload = static::jsonDecode(static::urlsafeB64Decode($bodyb64))) {
            throw new UnexpectedValueException('Invalid claims encoding');
        }
        if (false === ($sig = static::urlsafeB64Decode($cryptob64))) {
            throw new UnexpectedValueException('Invalid signature encoding');
        }
        if (empty($header->alg)) {
            throw new UnexpectedValueException('Empty algorithm');
        }
        if (empty(static::$supported_algs[$header->alg])) {
            throw new UnexpectedValueException('Algorithm not supported');
        }
        if (!in_array($header->alg, $allowed_algs)) {
            throw new UnexpectedValueException('Algorithm not allowed');
        }
        if ($header->alg === 'ES256') {
            // OpenSSL expects an ASN.1 DER sequence for ES256 signatures
            $sig = self::signatureToDER($sig);
        }

        if (is_array($key) || $key instanceof \ArrayAccess) {
            if (isset($header->kid)) {
                if (!isset($key[$header->kid])) {
                    throw new UnexpectedValueException('"kid" invalid, unable to lookup correct key');
                }
                $key = $key[$header->kid];
            } else {
                throw new UnexpectedValueException('"kid" empty, unable to lookup correct key');
            }
        }

        // Check the signature
        if (!static::verify("$headb64.$bodyb64", $sig, $key, $header->alg)) {
            throw new SignatureInvalidException('Signature verification failed');
        }

        // Check the nbf if it is defined. This is the time that the
        // token can actually be used. If it's not yet that time, abort.
        if (isset($payload->nbf) && $payload->nbf > ($timestamp + static::$leeway)) {
            throw new BeforeValidException('Cannot handle token prior to ' . date(DateTime::ISO8601, $payload->nbf));
        }

        // Check that this token has been created before 'now'. This prevents
        // using tokens that have been created for later use (and haven't
        // correctly used the nbf claim).
        if (isset($payload->iat) && $payload->iat > ($timestamp + static::$leeway)) {
            throw new BeforeValidException('Cannot handle token prior to ' . date(DateTime::ISO8601, $payload->iat));
        }

        // Check if this token has expired.
        if (isset($payload->exp) && ($timestamp - static::$leeway) >= $payload->exp) {
            throw new ExpiredException('Expired token');
        }

        return $payload;
    }

    /**
     * Converts and signs a PHP object or array into a JWT string.
     *
     * @param object|array $payload     PHP object or array
     * @param string       $key         The secret key.
     *                                  If the algorithm used is asymmetric, this is the private key
     * @param string       $alg         The signing algorithm.
     *                                  Supported algorithms are 'ES256', 'HS256', 'HS384', 'HS512', 'RS256', 'RS384',
     *                                  and 'RS512'
     * @param mixed        $keyId
     * @param array        $head        An array with header elements to attach
     *
     * @return string A signed JWT
     *
     * @uses jsonEncode
     * @uses urlsafeB64Encode
     */
    public static function encode($payload, $key, $alg = 'HS256', $keyId = null, $head = null) {
        $header = array(
            'typ' => 'JWT',
            'alg' => $alg
        );
        if ($keyId !== null) {
            $header['kid'] = $keyId;
        }
        if (isset($head) && is_array($head)) {
            $header = array_merge($head, $header);
        }
        $segments      = array();
        $segments[]    = static::urlsafeB64Encode(static::jsonEncode($header));
        $segments[]    = static::urlsafeB64Encode(static::jsonEncode($payload));
        $signing_input = implode('.', $segments);

        $signature  = static::sign($signing_input, $key, $alg);
        $segments[] = static::urlsafeB64Encode($signature);

        return implode('.', $segments);
    }

    /**
     * Sign a string with a given key and algorithm.
     *
     * @param string          $msg      The message to sign
     * @param string|resource $key      The secret key
     * @param string          $alg      The signing algorithm.
     *                                  Supported algorithms are 'ES256', 'HS256', 'HS384', 'HS512', 'RS256', 'RS384',
     *                                  and 'RS512'
     *
     * @return string An encrypted message
     *
     * @throws DomainException Unsupported algorithm was specified
     */
    public static function sign($msg, $key, $alg = 'HS256') {
        if (empty(static::$supported_algs[$alg])) {
            throw new DomainException('Algorithm not supported');
        }
        list($function, $algorithm) = static::$supported_algs[$alg];
        switch ($function) {
            case 'hash_hmac':
                return hash_hmac($algorithm, $msg, $key, true);
            case 'openssl':
                $signature = '';
                $success   = openssl_sign($msg, $signature, $key, $algorithm);
                if (!$success) {
                    throw new DomainException("OpenSSL unable to sign data");
                } else {
                    if ($alg === 'ES256') {
                        $signature = self::signatureFromDER($signature, 256);
                    }

                    return $signature;
                }
        }
    }

    /**
     * Verify a signature with the message, key and method. Not all methods
     * are symmetric, so we must have a separate verify and sign method.
     *
     * @param string          $msg       The original message (header and body)
     * @param string          $signature The original signature
     * @param string|resource $key       For HS*, a string key works. for RS*, must be a resource of an openssl public
     *                                   key
     * @param string          $alg       The algorithm
     *
     * @return bool
     *
     * @throws DomainException Invalid Algorithm or OpenSSL failure
     */
    private static function verify($msg, $signature, $key, $alg) {
        if (empty(static::$supported_algs[$alg])) {
            throw new DomainException('Algorithm not supported');
        }

        list($function, $algorithm) = static::$supported_algs[$alg];
        switch ($function) {
            case 'openssl':
                $success = openssl_verify($msg, $signature, $key, $algorithm);
                if ($success === 1) {
                    return true;
                } elseif ($success === 0) {
                    return false;
                }
                // returns 1 on success, 0 on failure, -1 on error.
                throw new DomainException('OpenSSL error: ' . openssl_error_string());
            case 'hash_hmac':
            default:
                $hash = hash_hmac($algorithm, $msg, $key, true);
                if (function_exists('hash_equals')) {
                    return hash_equals($signature, $hash);
                }
                $len = min(static::safeStrlen($signature), static::safeStrlen($hash));

                $status = 0;
                for ($i = 0; $i < $len; $i++) {
                    $status |= (ord($signature[$i]) ^ ord($hash[$i]));
                }
                $status |= (static::safeStrlen($signature) ^ static::safeStrlen($hash));

                return ($status === 0);
        }
    }

    /**
     * Decode a JSON string into a PHP object.
     *
     * @param string $input JSON string
     *
     * @return object Object representation of JSON string
     *
     * @throws DomainException Provided string was invalid JSON
     */
    public static function jsonDecode($input) {
        if (version_compare(PHP_VERSION, '5.4.0', '>=') && !(defined('JSON_C_VERSION') && PHP_INT_SIZE > 4)) {
            /** In PHP >=5.4.0, json_decode() accepts an options parameter, that allows you
             * to specify that large ints (like Steam Transaction IDs) should be treated as
             * strings, rather than the PHP default behaviour of converting them to floats.
             */
            $obj = json_decode($input, false, 512, JSON_BIGINT_AS_STRING);
        } else {
            /** Not all servers will support that, however, so for older versions we must
             * manually detect large ints in the JSON string and quote them (thus converting
             *them to strings) before decoding, hence the preg_replace() call.
             */
            $max_int_length       = strlen((string)PHP_INT_MAX) - 1;
            $json_without_bigints = preg_replace('/:\s*(-?\d{' . $max_int_length . ',})/', ': "$1"', $input);
            $obj                  = json_decode($json_without_bigints);
        }

        if ($errno = json_last_error()) {
            static::handleJsonError($errno);
        } elseif ($obj === null && $input !== 'null') {
            throw new DomainException('Null result with non-null input');
        }

        return $obj;
    }

    /**
     * Encode a PHP object into a JSON string.
     *
     * @param object|array $input A PHP object or array
     *
     * @return string JSON representation of the PHP object or array
     *
     * @throws DomainException Provided object could not be encoded to valid JSON
     */
    public static function jsonEncode($input) {
        $json = json_encode($input);
        if ($errno = json_last_error()) {
            static::handleJsonError($errno);
        } elseif ($json === 'null' && $input !== null) {
            throw new DomainException('Null result with non-null input');
        }

        return $json;
    }

    /**
     * Decode a string with URL-safe Base64.
     *
     * @param string $input A Base64 encoded string
     *
     * @return string A decoded string
     */
    public static function urlsafeB64Decode($input) {
        $remainder = strlen($input) % 4;
        if ($remainder) {
            $padlen = 4 - $remainder;
            $input  .= str_repeat('=', $padlen);
        }

        return base64_decode(strtr($input, '-_', '+/'));
    }

    /**
     * Encode a string with URL-safe Base64.
     *
     * @param string $input The string you want encoded
     *
     * @return string The base64 encode of what you passed in
     */
    public static function urlsafeB64Encode($input) {
        return str_replace('=', '', strtr(base64_encode($input), '+/', '-_'));
    }

    /**
     * Helper method to create a JSON error.
     *
     * @param int $errno An error number from json_last_error()
     *
     * @return void
     */
    private static function handleJsonError($errno) {
        $messages = array(
            JSON_ERROR_DEPTH          => 'Maximum stack depth exceeded',
            JSON_ERROR_STATE_MISMATCH => 'Invalid or malformed JSON',
            JSON_ERROR_CTRL_CHAR      => 'Unexpected control character found',
            JSON_ERROR_SYNTAX         => 'Syntax error, malformed JSON',
            JSON_ERROR_UTF8           => 'Malformed UTF-8 characters'
            //PHP >= 5.3.3
        );
        throw new DomainException(isset($messages[$errno]) ? $messages[$errno] : 'Unknown JSON error: ' . $errno);
    }

    /**
     * Get the number of bytes in cryptographic strings.
     *
     * @param string $str
     *
     * @return int
     */
    private static function safeStrlen($str) {
        if (function_exists('mb_strlen')) {
            return mb_strlen($str, '8bit');
        }

        return strlen($str);
    }

    /**
     * Convert an ECDSA signature to an ASN.1 DER sequence
     *
     * @param string $sig The ECDSA signature to convert
     *
     * @return  string The encoded DER object
     */
    private static function signatureToDER($sig) {
        // Separate the signature into r-value and s-value
        list($r, $s) = str_split($sig, (int)(strlen($sig) / 2));

        // Trim leading zeros
        $r = ltrim($r, "\x00");
        $s = ltrim($s, "\x00");

        // Convert r-value and s-value from unsigned big-endian integers to
        // signed two's complement
        if (ord($r[0]) > 0x7f) {
            $r = "\x00" . $r;
        }
        if (ord($s[0]) > 0x7f) {
            $s = "\x00" . $s;
        }

        return self::encodeDER(self::ASN1_SEQUENCE, self::encodeDER(self::ASN1_INTEGER, $r) . self::encodeDER(self::ASN1_INTEGER, $s));
    }

    /**
     * Encodes a value into a DER object.
     *
     * @param int    $type  DER tag
     * @param string $value the value to encode
     *
     * @return  string  the encoded object
     */
    private static function encodeDER($type, $value) {
        $tag_header = 0;
        if ($type === self::ASN1_SEQUENCE) {
            $tag_header |= 0x20;
        }

        // Type
        $der = chr($tag_header | $type);

        // Length
        $der .= chr(strlen($value));

        return $der . $value;
    }

    /**
     * Encodes signature from a DER object.
     *
     * @param string $der     binary signature in DER format
     * @param int    $keySize the nubmer of bits in the key
     *
     * @return  string  the signature
     */
    private static function signatureFromDER($der, $keySize) {
        // OpenSSL returns the ECDSA signatures as a binary ASN.1 DER SEQUENCE
        list($offset, $_) = self::readDER($der);
        list($offset, $r) = self::readDER($der, $offset);
        list($offset, $s) = self::readDER($der, $offset);

        // Convert r-value and s-value from signed two's compliment to unsigned
        // big-endian integers
        $r = ltrim($r, "\x00");
        $s = ltrim($s, "\x00");

        // Pad out r and s so that they are $keySize bits long
        $r = str_pad($r, $keySize / 8, "\x00", STR_PAD_LEFT);
        $s = str_pad($s, $keySize / 8, "\x00", STR_PAD_LEFT);

        return $r . $s;
    }

    /**
     * Reads binary DER-encoded data and decodes into a single object
     *
     * @param string $der    the binary data in DER format
     * @param int    $offset the offset of the data stream containing the object
     *                       to decode
     *
     * @return array [$offset, $data] the new offset and the decoded object
     */
    private static function readDER($der, $offset = 0) {
        $pos         = $offset;
        $size        = strlen($der);
        $constructed = (ord($der[$pos]) >> 5) & 0x01;
        $type        = ord($der[$pos++]) & 0x1f;

        // Length
        $len = ord($der[$pos++]);
        if ($len & 0x80) {
            $n   = $len & 0x1f;
            $len = 0;
            while ($n-- && $pos < $size) {
                $len = ($len << 8) | ord($der[$pos++]);
            }
        }

        // Value
        if ($type == self::ASN1_BIT_STRING) {
            $pos++; // Skip the first contents octet (padding indicator)
            $data = substr($der, $pos, $len - 1);
            $pos  += $len - 1;
        } elseif (!$constructed) {
            $data = substr($der, $pos, $len);
            $pos  += $len;
        } else {
            $data = null;
        }

        return array(
            $pos,
            $data
        );
    }
}