import 'dart:async';
import 'dart:io';

import 'package:crypto/crypto.dart';
import 'package:dio/dio.dart';
import 'package:path_provider/path_provider.dart';
import 'package:miaoji_zhang/shared/update/update_installer.dart';
import 'package:miaoji_zhang/shared/update/update_models.dart';

class UpdateDownloadProgress {
  final int received;
  final int total;
  final double bytesPerSecond;

  const UpdateDownloadProgress({
    required this.received,
    required this.total,
    required this.bytesPerSecond,
  });

  double? get fraction => total > 0 ? (received / total).clamp(0, 1) : null;
}

class UpdateDownloadException implements Exception {
  final String message;
  const UpdateDownloadException(this.message);

  @override
  String toString() => message;
}

class UpdateDownloader {
  UpdateDownloader({Dio? dio})
    : _dio =
          dio ??
          Dio(
            BaseOptions(
              connectTimeout: const Duration(seconds: 15),
              receiveTimeout: const Duration(minutes: 10),
              followRedirects: true,
              maxRedirects: 5,
            ),
          );

  final Dio _dio;
  CancelToken? _cancelToken;

  bool get isDownloading => _cancelToken != null;

  void cancel() => _cancelToken?.cancel('用户取消下载');

  Future<void> cleanupStale() async {
    if (!Platform.isAndroid) return;
    final directory = await _updateDirectory();
    if (!await directory.exists()) return;
    final cutoff = DateTime.now().subtract(const Duration(hours: 24));
    await for (final entity in directory.list()) {
      if (entity is! File) continue;
      final stat = await entity.stat();
      if (entity.path.endsWith('.part') || stat.modified.isBefore(cutoff)) {
        await _delete(entity);
      }
    }
  }

  Future<String> downloadAndVerify(
    AppRelease release, {
    required void Function(UpdateDownloadProgress progress) onProgress,
  }) async {
    if (_cancelToken != null) {
      throw const UpdateDownloadException('更新包正在下载中');
    }
    final uri = Uri.tryParse(release.downloadUrl);
    if (uri == null || uri.scheme != 'https' || uri.host.isEmpty) {
      throw const UpdateDownloadException('更新包地址无效，必须使用 HTTPS');
    }
    final expectedSha = release.sha256?.trim().toLowerCase();
    if (expectedSha == null ||
        !RegExp(r'^[0-9a-f]{64}$').hasMatch(expectedSha)) {
      throw const UpdateDownloadException('发布记录缺少有效的 SHA-256，已禁止安装');
    }

    final directory = await _updateDirectory();
    await directory.create(recursive: true);
    final partial = File(
      '${directory.path}${Platform.pathSeparator}jizhi-${release.buildNumber}.apk.part',
    );
    final target = File(
      '${directory.path}${Platform.pathSeparator}jizhi-${release.buildNumber}.apk',
    );
    await _delete(partial);
    await _delete(target);

    final token = CancelToken();
    _cancelToken = token;
    final stopwatch = Stopwatch()..start();
    var lastBytes = 0;
    var lastElapsed = Duration.zero;
    var keepTarget = false;
    try {
      await _dio.download(
        release.downloadUrl,
        partial.path,
        cancelToken: token,
        deleteOnError: true,
        onReceiveProgress: (received, total) {
          final elapsed = stopwatch.elapsed;
          final deltaMicros = (elapsed - lastElapsed).inMicroseconds;
          final speed = deltaMicros <= 0
              ? 0.0
              : (received - lastBytes) *
                    Duration.microsecondsPerSecond /
                    deltaMicros;
          if (elapsed - lastElapsed >= const Duration(milliseconds: 250) ||
              received == total) {
            lastBytes = received;
            lastElapsed = elapsed;
            onProgress(
              UpdateDownloadProgress(
                received: received,
                total: total > 0 ? total : release.fileSize ?? 0,
                bytesPerSecond: speed,
              ),
            );
          }
        },
      );

      final actualSize = await partial.length();
      if (release.fileSize case final expectedSize?
          when expectedSize > 0 && actualSize != expectedSize) {
        throw UpdateDownloadException(
          '更新包大小不一致（预期 $expectedSize 字节，实际 $actualSize 字节）',
        );
      }
      final actualSha = (await sha256.bind(partial.openRead()).first)
          .toString();
      if (actualSha.toLowerCase() != expectedSha) {
        throw const UpdateDownloadException('更新包完整性校验失败，文件已删除');
      }
      await partial.rename(target.path);
      final inspection = await UpdateInstaller.inspect(
        path: target.path,
        expectedBuild: release.buildNumber,
      );
      if (!inspection.valid) {
        throw UpdateDownloadException(inspection.message ?? '更新包身份校验失败，文件已删除');
      }
      keepTarget = true;
      return target.path;
    } on DioException catch (error) {
      if (CancelToken.isCancel(error)) {
        throw const UpdateDownloadException('下载已取消');
      }
      throw const UpdateDownloadException('更新包下载失败，请检查网络后重试');
    } on UpdateDownloadException {
      rethrow;
    } catch (_) {
      throw const UpdateDownloadException('更新包处理失败，请重新下载');
    } finally {
      _cancelToken = null;
      stopwatch.stop();
      if (!keepTarget) {
        await _delete(partial);
        await _delete(target);
      }
    }
  }

  Future<void> deleteFile(String path) => _delete(File(path));

  Future<void> scheduleCleanup(String path) async {
    unawaited(
      Future<void>.delayed(const Duration(minutes: 10), () async {
        await _delete(File(path));
      }),
    );
  }

  Future<Directory> _updateDirectory() async {
    final temporary = await getTemporaryDirectory();
    return Directory('${temporary.path}${Platform.pathSeparator}updates');
  }

  Future<void> _delete(File file) async {
    try {
      if (await file.exists()) await file.delete();
    } catch (_) {}
  }
}