import 'dart:convert';
import 'dart:typed_data';

import 'package:crypto/crypto.dart';
import 'package:encrypt/encrypt.dart';

/// 新版本解密（项目自定义协议：12 字节 nonce + sha256 派生 key/iv + AES-CBC）
String aesDecryptEx(String cipher, String key) {
  // final t1 = DateTime.now();
  const nonceLen = 12;
  final cipherBytes = base64Decode(cipher);
  final nonce = cipherBytes.sublist(0, nonceLen);
  final largeShaRaw = [...utf8.encode(key), ...nonce];
  final largeShaRawMid = largeShaRaw.length ~/ 2;
  final msgKeyLarge = sha256.convert(largeShaRaw).bytes;
  final msgKey = msgKeyLarge.sublist(8, 24);

  final shaRawA = [...msgKey, ...largeShaRaw.sublist(0, largeShaRawMid)];
  final sha256a = sha256.convert(shaRawA).bytes;

  final shaRawB = [...largeShaRaw.sublist(largeShaRawMid), ...msgKey];
  final sha256b = sha256.convert(shaRawB).bytes;

  final aesKey = [...sha256a.sublist(0, 8), ...sha256b.sublist(8, 24), ...sha256a.sublist(24)];

  final aesIV = [...sha256b.sublist(0, 4), ...sha256a.sublist(12, 20), ...sha256b.sublist(28)];

  final encrypter = Encrypter(AES(Key(Uint8List.fromList(aesKey)), mode: AESMode.cbc));
  final decrypted = encrypter.decryptBytes(Encrypted(cipherBytes.sublist(nonceLen)), iv: IV(Uint8List.fromList(aesIV)));
  final text = const Utf8Decoder().convert(decrypted);
  return text;
}