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

import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
import 'package:url_launcher/url_launcher.dart';

import 'installer.dart';

/// 强制更新页：检测到新版本时的全屏阻塞页。
/// PopScope 禁返回（Android 系统返回 / iOS 边缘滑动均不可退出）。
/// 点「立即更新」在 App 内流式下载 APK（显示下载进度）→ PackageInstaller
/// 会话安装（显示安装进度），不再跳浏览器。
/// 点击更新时回调 onUpdateAccepted（调用方持久化服务器版本号，
/// 使 APK 版本号不递增时也不反复提示）。
class UpdateScreen extends StatefulWidget {
  final String version;
  final String url;
  final String notes;
  final VoidCallback? onUpdateAccepted;

  const UpdateScreen({
    super.key,
    required this.version,
    required this.url,
    this.notes = '',
    this.onUpdateAccepted,
  });

  @override
  State<UpdateScreen> createState() => _UpdateScreenState();
}

enum _Stage { idle, downloading, installing, finished, failed }

class _UpdateScreenState extends State<UpdateScreen> {
  final http.Client _client = http.Client();
  final File _apkFile = File('${Directory.systemTemp.path}/observer-latest.apk');
  final File _apkPart =
      File('${Directory.systemTemp.path}/observer-latest.apk.part');

  _Stage _stage = _Stage.idle;

  /// 进度百分比 0-100；null = 总量未知（不确定进度条）
  double? _progress;
  String? _message;
  StreamSubscription<InstallEvent>? _installSub;

  @override
  void dispose() {
    _installSub?.cancel();
    _client.close();
    super.dispose();
  }

  Future<void> _launch() async {
    if (_stage == _Stage.downloading ||
        _stage == _Stage.installing ||
        _stage == _Stage.finished) {
      return;
    }
    setState(() {
      _stage = _Stage.idle;
      _message = null;
    });
    widget.onUpdateAccepted?.call();
    if (!Platform.isAndroid) {
      // 更新检查本就仅 Android 触发，这里兜底非 Android 走浏览器
      final uri = Uri.tryParse(widget.url);
      if (uri == null) return;
      try {
        await launchUrl(uri, mode: LaunchMode.externalApplication);
      } catch (_) {}
      return;
    }
    // APK 已下载完成（下载是原子落盘，.part 改名后文件才存在）→ 跳过下载直接安装
    if (_apkFile.existsSync()) {
      await _install();
      return;
    }
    await _download();
  }

  Future<void> _download() async {
    setState(() {
      _stage = _Stage.downloading;
      _progress = 0;
    });
    try {
      if (_apkPart.existsSync()) _apkPart.deleteSync();
      final res = await _client.send(http.Request('GET', Uri.parse(widget.url)));
      if (res.statusCode != 200) {
        throw HttpException('HTTP ${res.statusCode}');
      }
      final total = res.contentLength ?? -1;
      final sink = _apkPart.openWrite();
      var received = 0;
      await for (final chunk in res.stream) {
        sink.add(chunk);
        received += chunk.length;
        if (mounted && total > 0) {
          setState(() => _progress = received / total * 100);
        }
      }
      await sink.close();
      // 原子落盘：下载完成后才重命名为正式文件，避免残留半包被当成完整 APK
      _apkPart.renameSync(_apkFile.path);
      if (!mounted) return;
      await _install();
    } catch (_) {
      if (_apkPart.existsSync()) _apkPart.deleteSync();
      if (!mounted) return;
      setState(() {
        _stage = _Stage.failed;
        _progress = null;
        _message = '下载失败，请检查网络后重试';
      });
    }
  }

  Future<void> _install() async {
    setState(() {
      _stage = _Stage.installing;
      _progress = 0;
      _message = null;
    });
    await _installSub?.cancel();
    _installSub = ApkInstaller.progress().listen((e) {
      if (!mounted) return;
      switch (e.event) {
        case 'progress':
          setState(() => _progress = e.progress.toDouble());
          break;
        case 'finished':
          final ok = e.success == true;
          setState(() {
            _stage = ok ? _Stage.finished : _Stage.failed;
            _message = ok ? '安装完成，请从桌面打开新版应用' : '安装失败，请重试';
          });
          break;
        case 'failed':
          setState(() {
            _stage = _Stage.failed;
            _message = e.error ?? '安装失败，请重试';
          });
          break;
      }
    }, onError: (Object _) {
      if (!mounted) return;
      setState(() {
        _stage = _Stage.failed;
        _message = '安装失败，请重试';
      });
    });
    final result = await ApkInstaller.install(_apkFile.path);
    if (!mounted) return;
    if (result == 'permission_required') {
      // 原生侧已拉起系统设置页；APK 已缓存，用户开启后返回再点直达安装
      setState(() {
        _stage = _Stage.failed;
        _message = '请在系统设置中允许「安装未知应用」，返回后再次点击「立即更新」（APK 已缓存，无需重新下载）';
      });
    }
  }

  @override
  Widget build(BuildContext context) {
    final theme = Theme.of(context);
    final busy = _stage == _Stage.downloading || _stage == _Stage.installing;
    final progressText = _stage == _Stage.downloading
        ? (_progress == null ? '下载中…' : '下载中 ${_progress!.round()}%')
        : (_progress == null ? '安装中…' : '安装中 ${_progress!.round()}%');

    return PopScope(
      canPop: false,
      child: Scaffold(
        body: Center(
          child: Padding(
            padding: const EdgeInsets.all(32),
            child: Column(
              mainAxisSize: MainAxisSize.min,
              children: [
                Icon(Icons.system_update_alt,
                    size: 64, color: theme.colorScheme.primary),
                const SizedBox(height: 16),
                Text('发现新版本 ${widget.version}',
                    style: theme.textTheme.headlineSmall),
                const SizedBox(height: 12),
                if (widget.notes.isNotEmpty)
                  Text(widget.notes,
                      textAlign: TextAlign.center,
                      style: const TextStyle(height: 1.6)),
                const SizedBox(height: 24),
                if (busy) ...[
                  LinearProgressIndicator(
                    value: _progress == null ? null : _progress! / 100,
                    minHeight: 6,
                  ),
                  const SizedBox(height: 12),
                  Text(progressText),
                  const SizedBox(height: 24),
                ],
                FilledButton.icon(
                  onPressed: busy || _stage == _Stage.finished
                      ? null
                      : _launch,
                  icon: const Icon(Icons.download),
                  label: Text(_stage == _Stage.finished ? '已完成' : '立即更新'),
                  style: FilledButton.styleFrom(
                    minimumSize: const Size(200, 48),
                    textStyle: const TextStyle(fontSize: 16),
                  ),
                ),
                if (_message != null) ...[
                  const SizedBox(height: 12),
                  Text(
                    _message!,
                    textAlign: TextAlign.center,
                    style: TextStyle(
                      height: 1.5,
                      color: _stage == _Stage.failed
                          ? theme.colorScheme.error
                          : Colors.green,
                    ),
                  ),
                ],
                const SizedBox(height: 12),
                Text('不更新将无法继续使用',
                    style: theme.textTheme.bodySmall
                        ?.copyWith(color: theme.colorScheme.error)),
              ],
            ),
          ),
        ),
      ),
    );
  }
}