<?php

/**
 * +----------------------------------------------------------------------
 * | Created By PhpStorm
 * +----------------------------------------------------------------------
 * | DATE: 2021/8/2
 * +----------------------------------------------------------------------
 * | TIME: 9:59
 * +----------------------------------------------------------------------
 * | Author: YangXing(925032253@qq.com)
 * +----------------------------------------------------------------------
 * | Class: jwt
 * +----------------------------------------------------------------------
 */

namespace servers\jwt;


class jwt
{
    //头部
    private static $header = [
        //生成signature的算法
        'alg'    =>    'HS256',
        //类型
        'typ'    =>    'JWT'
    ];

    //使用HMAC生成信息摘要时所使用的密钥
    private static $key = '19830901';

    /**
     * 获取jwt token
     * @param array $payload jwt载荷   格式如下非必须
     * [
     *  'iss'=>'jwt_admin',  //该JWT的签发者
     *  'iat'=>time(),  //签发时间
     *  'exp'=>time()+7200,  //过期时间
     *  'nbf'=>time()+60,  //该时间之前不接收处理该Token
     *  'sub'=>'www.admin.com',  //面向的用户
     *  'jti'=>md5(uniqid('JWT').time())  //该Token唯一标识
     * ]
     * @return bool|string
     */
    public static function getToken(array $payload)
    {
        if (!is_array($payload)) return false;
        $base64header = self::base64UrlEncode(json_encode(self::$header,JSON_UNESCAPED_UNICODE));
        $base64payload = self::base64UrlEncode(json_encode($payload,JSON_UNESCAPED_UNICODE));
        return $base64header.'.'.$base64payload.'.'.self::signature($base64header.'.'.$base64payload,self::$key,self::$header['alg']);
    }

    /**
     * 验证token是否有效,默认验证exp,nbf,iat时间
     * @param string $token 需要验证的token
     * @return bool|string
     */
    public static function verifyToken(string $token)
    {
        $tokens = explode('.', $token);
        if (count($tokens) != 3) return false;
        list($base64header, $base64payload, $sign) = $tokens;

        //获取jwt算法
        $base64decodeheader = json_decode(self::base64UrlDecode($base64header), JSON_OBJECT_AS_ARRAY);
        if (empty($base64decodeheader['alg']) && empty($base64decodeheader['typ'])) return false;

        //签名验证
        if (self::signature($base64header . '.' . $base64payload, self::$key, $base64decodeheader['alg']) !== $sign) return false;

        $payload = json_decode(self::base64UrlDecode($base64payload), JSON_OBJECT_AS_ARRAY);

        //签发时间大于当前服务器时间验证失败
        if (isset($payload['iat']) && $payload['iat'] > time()) return false;

        //过期时间小宇当前服务器时间验证失败
        if (isset($payload['exp']) && $payload['exp'] < time()) return false;

        //该nbf时间之前不接收处理该Token
        if (isset($payload['nbf']) && $payload['nbf'] > time()) return false;

        return $payload;
    }

    /**
     * base64UrlEncode   https://jwt.io/  中base64UrlEncode编码实现
     * @param string $input 需要编码的字符串
     * @return string
     */
    private static function base64UrlEncode(string $input)
    {
        return str_replace('=', '', strtr(base64_encode($input), '+/', '-_'));
    }

    /**
     * base64UrlEncode  https://jwt.io/  中base64UrlEncode解码实现
     * @param string $input 需要解码的字符串
     * @return bool|string
     */
    private static function base64UrlDecode(string $input)
    {
        $remainder = strlen($input) % 4;
        if ($remainder) {
            $addlen = 4 - $remainder;
            $input .= str_repeat('=', $addlen);
        }
        return base64_decode(strtr($input, '-_', '+/'));
    }

    /**
     * HMACSHA256签名   https://jwt.io/  中HMACSHA256签名实现
     * @param string $input 为base64UrlEncode(header).".".base64UrlEncode(payload)
     * @param string $key
     * @param string $alg   算法方式
     * @return mixed
     */
    private static function signature(string $input, string $key, string $alg = 'HS256')
    {
        $alg_config = ['HS256' => 'sha256'];
        return self::base64UrlEncode(hash_hmac($alg_config[$alg], $input, $key,true));
    }
}