<?php

namespace App\Service;

class DingTalkCrypto
{
    protected string $token;
    protected string $encodingAesKey; // URL safe base64 字符串，长度 43

    public function __construct(string $token, string $encodingAesKey)
    {
        $this->token = $token;
        $this->encodingAesKey = $encodingAesKey;
    }

    /**
     * 解密钉钉事件回调消息
     *
     * @param string $signature URL参数 signature
     * @param string $timestamp URL参数 timestamp
     * @param string $nonce URL参数 nonce
     * @param string $encrypt 消息体 encrypt
     * @return array|false
     */
    public function decryptMsg(string $msgSignature, string $timestamp, string $nonce, string $encrypt)
    {
        // 验签
        $tmpArr = [$this->token, $timestamp, $nonce, $encrypt];
        sort($tmpArr, SORT_STRING);
        $tmpStr = implode('', $tmpArr);
        $hash = sha1($tmpStr);
        if ($hash !== $msgSignature) {
            return false;
        }

        // AES 解密
        $aesKey = base64_decode($this->encodingAesKey . '='); // 补足 padding
        $iv = substr($aesKey, 0, 16);
        $cipherText = base64_decode($encrypt);
        $decrypted = openssl_decrypt($cipherText, 'AES-256-CBC', $aesKey, OPENSSL_ZERO_PADDING, $iv);
        if ($decrypted === false) return false;

        // 去掉 padding
        $decrypted = $this->pkcs7Unpad($decrypted);

        // 去掉前16位随机字符串
        $content = substr($decrypted, 16);

        // 读取消息长度
        $lenList = unpack("N", substr($content, 0, 4));
        $jsonLen = $lenList[1];

        // 获取 JSON
        $json = substr($content, 4, $jsonLen);

        return json_decode($json, true);
    }

    /**
     * 加密返回给钉钉的消息
     *
     * @param string $replyMsg 明文消息
     * @param string $timestamp
     * @param string $nonce
     * @return array
     */
    public function encryptMsg(string $replyMsg, string $timestamp, string $nonce): array
    {
        $random16 = $this->getRandomStr(16);
        $msgLenBin = pack("N", strlen($replyMsg));
        $corpId = ''; // 不需要corpId

        $plain = $random16 . $msgLenBin . $replyMsg . $corpId;

        // PKCS#7 padding
        $blockSize = 32;
        $pad = $blockSize - (strlen($plain) % $blockSize);
        $pad = $pad === 0 ? $blockSize : $pad;
        $plainPadded = $plain . str_repeat(chr($pad), $pad);

        // AES 加密
        $aesKey = base64_decode($this->encodingAesKey);
        $iv = substr($aesKey, 0, 16);
        $encrypted = openssl_encrypt($plainPadded, 'AES-256-CBC', $aesKey, OPENSSL_ZERO_PADDING, $iv);
        $encryptBase64 = base64_encode($encrypted);

        // 计算 msg_signature
        $signatureStr = $this->token . $timestamp . $nonce . $encryptBase64;
        $msgSignature = sha1($signatureStr);

        return [
            'msg_signature' => $msgSignature,
            'encrypt'       => $encryptBase64
        ];
    }

    private function getRandomStr(int $length = 16): string
    {
        $chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
        $str = '';
        for ($i = 0; $i < $length; $i++) {
            $str .= $chars[random_int(0, strlen($chars) - 1)];
        }
        return $str;
    }

    private function pkcs7Unpad(string $text)
    {
        $pad = ord(substr($text, -1));
        if ($pad < 1 || $pad > 32) return false;
        return substr($text, 0, -$pad);
    }
}