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

import 'package:flutter/services.dart'
    show MethodChannel, PlatformException, MissingPluginException;

import '../app/app_version.dart';

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

Uri? updateDownloadUri(String value) {
  if (value.length > 2048 || RegExp(r'[\s\x00-\x1f\x7f]').hasMatch(value)) {
    return null;
  }
  final uri = Uri.tryParse(value);
  return uri != null &&
          uri.scheme == 'https' &&
          uri.host.isNotEmpty &&
          uri.userInfo.isEmpty
      ? uri
      : null;
}

class AppRelease {
  const AppRelease({
    required this.version,
    required this.buildNumber,
    required this.notes,
    required this.downloadUri,
  });
  final String version, notes;
  final int buildNumber;
  final Uri downloadUri;
}

class UpdateHttpResponse {
  const UpdateHttpResponse(this.status, this.body);
  final int status;
  final List<int> body;
}

abstract interface class UpdateTransport {
  Future<UpdateHttpResponse> get(Uri endpoint);
}

class IoUpdateTransport implements UpdateTransport {
  const IoUpdateTransport();
  @override
  Future<UpdateHttpResponse> get(Uri endpoint) async {
    final client = HttpClient()..connectionTimeout = const Duration(seconds: 8);
    Future<UpdateHttpResponse> fetch() async {
      final request = await client.getUrl(endpoint);
      request.followRedirects = false;
      request.headers.set('Accept', 'application/json');
      request.headers.set('Cache-Control', 'no-cache');
      final response = await request.close();
      final bytes = <int>[];
      await for (final chunk in response) {
        if (bytes.length + chunk.length > AppUpdateService.maxBytes) {
          throw const UpdateCheckException('更新信息过大，请稍后重试');
        }
        bytes.addAll(chunk);
      }
      return UpdateHttpResponse(response.statusCode, bytes);
    }

    try {
      return await fetch().timeout(const Duration(seconds: 12));
    } finally {
      client.close(force: true);
    }
  }
}

class AppUpdateService {
  AppUpdateService({
    this.transport = const IoUpdateTransport(),
    this.currentBuild = appBuildNumber,
    this.endpoint = const String.fromEnvironment(
      'UPDATE_ENDPOINT',
      defaultValue: 'https://app.glowtps.cn/v1/updates/android',
    ),
  });
  static const maxBytes = 64 * 1024;
  final UpdateTransport transport;
  final int currentBuild;
  final String endpoint;
  Future<AppRelease?>? _pending;

  Future<AppRelease?> check() {
    if (_pending != null) return _pending!;
    final future = _check();
    _pending = future;
    // Attach error handling here too, so cleanup never creates an unhandled
    // future when startup intentionally suppresses an unavailable server.
    unawaited(
      future.then<void>(
        (_) {
          _pending = null;
        },
        onError: (Object _, StackTrace _) {
          _pending = null;
        },
      ),
    );
    return future;
  }

  Future<AppRelease?> _check() async {
    try {
      final uri = updateDownloadUri(endpoint);
      if (uri == null || uri.fragment.isNotEmpty) {
        throw const UpdateCheckException('更新服务地址无效');
      }
      final response = await transport
          .get(uri)
          .timeout(const Duration(seconds: 13));
      if (response.status != 200 || response.body.length > maxBytes) {
        throw const UpdateCheckException('暂时无法获取更新，请稍后重试');
      }
      final data = jsonDecode(utf8.decode(response.body));
      if (data is! Map ||
          data['schema_version'] != 1 ||
          data['application_id'] != 'com.tpschedule.app' ||
          !data.containsKey('latest')) {
        throw const FormatException();
      }
      final latest = data['latest'];
      if (latest == null) return null;
      if (latest is! Map) throw const FormatException();
      final version = latest['version'],
          build = latest['build_number'],
          notes = latest['notes'],
          url = latest['download_url'];
      if (version is! String ||
          !RegExp(r'^\d{1,4}\.\d{1,4}\.\d{1,4}$').hasMatch(version) ||
          build is! int ||
          build < 1 ||
          build > 2100000000 ||
          notes is! String ||
          notes.trim().isEmpty ||
          notes.runes.length > 8000 ||
          url is! String) {
        throw const FormatException();
      }
      final download = updateDownloadUri(url);
      if (download == null) throw const FormatException();
      if (build <= currentBuild) return null;
      return AppRelease(
        version: version,
        buildNumber: build,
        notes: notes.trim(),
        downloadUri: download,
      );
    } on UpdateCheckException {
      rethrow;
    } on FormatException {
      throw const UpdateCheckException('更新信息格式异常，请稍后重试');
    } catch (_) {
      throw const UpdateCheckException('无法连接更新服务，请检查网络后重试');
    }
  }
}

typedef UpdateDownloadOpener = Future<bool> Function(Uri uri);

Future<bool> openUpdateInBrowser(Uri uri) async {
  if (updateDownloadUri(uri.toString()) == null) return false;
  try {
    return await const MethodChannel('com.tpschedule.app/updates')
            .invokeMethod<bool>('openDownload', {'url': uri.toString()}) ??
        false;
  } on PlatformException {
    return false;
  } on MissingPluginException {
    return false;
  }
}