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

import 'package:asn1lib/asn1lib.dart';
import 'package:pointycastle/api.dart';
import 'package:pointycastle/asymmetric/api.dart';
import 'package:pointycastle/asymmetric/pkcs1.dart';
import 'package:pointycastle/asymmetric/rsa.dart';

/// RSA 公钥加密（对应 iOS BasicModule/Util/RSAEncryption.swift）。
///
/// - 算法：RSA / PKCS#1 v1.5 padding（与 iOS `SecKeyCreateEncryptedData` +
///   `.rsaEncryptionPKCS1` 完全对齐）
/// - 公钥格式：DER-SPKI Base64（X.509 SubjectPublicKeyInfo）
/// - 输出：标准 Base64（与服务端 `Base64.getDecoder()` 兼容）
///
/// 用法：
/// ```dart
/// final cipher = RsaHelper.encrypt(
///   'myPassword',
///   publicKeyDerBase64: Env.rsaPublicKey,
/// );
/// ```
///
/// 真实公钥 = `Env.rsaPublicKey`（--dart-define 注入；当前 Env 默认值 = iOS dev 公钥）。
class RsaHelper {
  RsaHelper._();

  /// 用公钥加密明文，返回 Base64 密文。
  ///
  /// **R-ROB-2 / 2026-05-10**：失败必须抛 [RsaEncryptionException]，**不允许返回 null** —
  /// 健康类 App 加密失败必须显式中断业务流，不允许调用方 fallback 到明文（合规底线）。
  /// 之前的 `String?` 签名依赖调用方人工 null 检查，新调用方易漏检导致请求送 "null" 串。
  static String encrypt(
    String plaintext, {
    required String publicKeyDerBase64,
  }) {
    // R-ROB-2 / 2026-05-10：拒绝空明文 — _processInBlocks 对 0 字节输入会返回空密文
    // （旧行为是 cipher='' 被 isNotNull 测试掩盖的 bug）；业务侧密码也不应为空
    if (plaintext.isEmpty) {
      throw RsaEncryptionException('明文为空，拒绝加密');
    }

    final RSAPublicKey pubKey;
    try {
      pubKey = _parseSpkiBase64(publicKeyDerBase64);
    } on Object catch (e, st) {
      throw RsaEncryptionException(
        'RSA 公钥解析失败：${e.runtimeType}',
        cause: e,
        stackTrace: st,
      );
    }

    try {
      final padding = PKCS1Encoding(RSAEngine())
        ..init(true, PublicKeyParameter<RSAPublicKey>(pubKey));

      final input = Uint8List.fromList(utf8.encode(plaintext));
      final output = _processInBlocks(padding, input);
      return base64.encode(output);
    } on Object catch (e, st) {
      throw RsaEncryptionException(
        'RSA 加密失败：${e.runtimeType}',
        cause: e,
        stackTrace: st,
      );
    }
  }

  /// 把 SPKI Base64 公钥（X.509 SubjectPublicKeyInfo）解析为 [RSAPublicKey]。
  ///
  /// 失败抛错（不再 swallow）— 上层 [encrypt] 统一转换为 [RsaEncryptionException]。
  static RSAPublicKey _parseSpkiBase64(String spkiBase64) {
    final bytes = base64.decode(spkiBase64.replaceAll(RegExp(r'\s+'), ''));
    final asn1Parser = ASN1Parser(bytes);
    final topLevelSeq = asn1Parser.nextObject() as ASN1Sequence;
    // SPKI: SEQUENCE { algorithm SEQUENCE { OID, NULL }, subjectPublicKey BIT STRING }
    final publicKeyBitString = topLevelSeq.elements[1] as ASN1BitString;
    final publicKeyAsn = ASN1Parser(publicKeyBitString.contentBytes());
    final publicKeySeq = publicKeyAsn.nextObject() as ASN1Sequence;
    final modulus = publicKeySeq.elements[0] as ASN1Integer;
    final exponent = publicKeySeq.elements[1] as ASN1Integer;
    return RSAPublicKey(
      modulus.valueAsBigInteger,
      exponent.valueAsBigInteger,
    );
  }

  static Uint8List _processInBlocks(
    AsymmetricBlockCipher engine,
    Uint8List input,
  ) {
    final numBlocks = (input.length / engine.inputBlockSize).ceil();
    final output = Uint8List(numBlocks * engine.outputBlockSize);
    var inputOffset = 0;
    var outputOffset = 0;
    while (inputOffset < input.length) {
      final size = (inputOffset + engine.inputBlockSize <= input.length)
          ? engine.inputBlockSize
          : input.length - inputOffset;
      final processed = engine.process(
        Uint8List.sublistView(input, inputOffset, inputOffset + size),
      );
      output.setRange(
        outputOffset,
        outputOffset + processed.length,
        processed,
      );
      inputOffset += size;
      outputOffset += processed.length;
    }
    return Uint8List.sublistView(output, 0, outputOffset);
  }
}

/// RSA 加密失败异常 — 调用方应 catch 并转为业务层 [Failure]（如 AuthFailure(cryptoFailed)），
/// **绝不允许** 把明文继续上送服务端。
class RsaEncryptionException implements Exception {
  RsaEncryptionException(this.message, {this.cause, this.stackTrace});

  final String message;
  final Object? cause;
  final StackTrace? stackTrace;

  @override
  String toString() => 'RsaEncryptionException: $message';
}