<?php

namespace app\extra\douyin;

class SignUtil
{
    /*
     * appid/client_key对应的client_secret TODO 这里换成服务商的appsecret
     */
    private static $secret = "12345678901234566543210987654321";
    private static $key;
    private static $iv;

    public static function init($secret) {
        self::$secret = $secret;
        self::$key = self::parseSecret(self::$secret);
        self::$iv = substr(self::$key, 16);
    }

    /**
     *  AES解密
     * @param string $data base64后的密文
     * @return string 明文
     */
    public static function decryptAES($data) {
        try {
            $encrypted = self::decode($data); // 先用base64解密
            $decrypted = openssl_decrypt(
                $encrypted,
                'AES-256-CBC',
                self::$key,
                OPENSSL_RAW_DATA,
                self::$iv
            );
            return $decrypted;
        } catch (\Exception $e) {
            error_log($e->getMessage());
            return null;
        }
    }

    /**
     * base64编码
     */
    public static function encode($data) {
        return base64_encode($data);
    }

    /**
     * base64解码
     */
    public static function decode($data) {
        return base64_decode($data);
    }

    private static function parseSecret($secret) {
        $secret = self::fillSecret($secret);
        $secret = self::cutSecret($secret);
        return $secret;
    }

    private static function cutSecret($secret) {
        if (strlen($secret) <= 32) {
            return $secret;
        }
        $rightCnt = (int)((strlen($secret) - 32) / 2);
        $leftCnt = strlen($secret) - 32 - $rightCnt;
        return substr($secret, $leftCnt, 32);
    }

    private static function fillSecret($secret) {
        if (strlen($secret) >= 32) {
            return $secret;
        }
        $rightCnt = (int)((32 - strlen($secret)) / 2);
        $leftCnt = 32 - strlen($secret) - $rightCnt;
        $sb = str_repeat('#', $leftCnt);
        $sb .= $secret;
        $sb .= str_repeat('#', $rightCnt);
        return $sb;
    }

}