<?php

namespace app\extra\dyLife;

class SignUtil
{

    private $secret;
    private $key;
    private $iv;

    public function init(string $secret = "") {
        $this->secret = $secret;
        $this->key = $this->parseSecret($secret);
        $this->iv = substr($this->key, 16);
        return $this;
    }

    /**
     * @Description AES解密
     * @param string $data base64后的密文
     * @return string 明文
     */
    public function decryptAES($data) {
        try {
            $encrypted = $this->decode($data); // 先用base64解密
            $decrypted = openssl_decrypt(
                $encrypted,
                'AES-256-CBC',
                $this->key,
                OPENSSL_RAW_DATA,
                $this->iv
            );
            return $decrypted;
        } catch (\Exception $e) {
//            error_log($e->getMessage());
            return null;
        }
    }

    /**
     * base64编码
     */
    public function encode($data) {
        return base64_encode($data);
    }

    /**
     * base64解码
     */
    public function decode($data) {
        return base64_decode($data);
    }

    private function parseSecret($secret) {
        $secret = $this->fillSecret($secret);
        $secret = $this->cutSecret($secret);
        return $secret;
    }

    private 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 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;
    }

}