import 'dart:io';
import 'package:flutter/foundation.dart';
import 'package:shared_preferences/shared_preferences.dart';
import 'package:flutter_saf/flutter_saf.dart';
import '../models/saf_permission_state.dart';

/// SAF 存储服务
/// 负责管理通过 SAF 授权的文件夹访问
class SafStorageService {
  static final SafStorageService _instance = SafStorageService._internal();
  factory SafStorageService() => _instance;
  SafStorageService._internal();

  static const String _prefKeySafUri = 'saf_storage_uri';
  static const String _prefKeySafPermission = 'saf_permission_uri';

  /// 存储的授权 URI
  String? _cachedUriString;

  /// 初始化，从 SharedPreferences 恢复授权状态
  Future<void> init() async {
    final prefs = await SharedPreferences.getInstance();
    _cachedUriString = prefs.getString(_prefKeySafUri);
    if (kDebugMode) {
      print('[SAF] 初始化，缓存 URI: $_cachedUriString');
    }
  }

  /// 获取当前授权状态
  Future<SafPermissionState> getPermissionState() async {
    if (_cachedUriString == null || _cachedUriString!.isEmpty) {
      return SafPermissionState.unauthorized;
    }

    try {
      final uri = Uri.parse(_cachedUriString!);
      // 检查 Uri 是否仍然有效
      final isValid = await FlutterSaf.isDirectory(uri);
      if (!isValid) {
        _clearCache();
        return SafPermissionState.expired;
      }
      return SafPermissionState.authorized;
    } catch (e) {
      _clearCache();
      return SafPermissionState.expired;
    }
  }

  /// 请求 SAF 授权（引导用户选择文件夹）
  /// 返回授权结果
  Future<SafAuthorizationResult> requestPermission() async {
    try {
      // 调用系统文件夹选择器
      // 引导用户选择 /storage/emulated/0/mbattery_charger/
      // 或者用户可以选择任何目录，但我们建议选择具体路径
      final uri = await FlutterSaf.openDocumentTree();

      if (uri == null) {
        return SafAuthorizationResult.denied();
      }

      // 获取持久化 URI 权限
      await FlutterSaf.takePersistableUriPermission(uri);

      // 验证是否为目录
      final isValid = await FlutterSaf.isDirectory(uri);
      if (!isValid) {
        return SafAuthorizationResult.error('选择的路径不是有效目录');
      }

      // 保存 URI
      final uriString = uri.toString();
      _cachedUriString = uriString;
      await _saveUri(uriString);

      if (kDebugMode) {
        print('[SAF] 授权成功，URI: $uriString');
      }

      return SafAuthorizationResult.success(uriString);
    } catch (e) {
      if (kDebugMode) {
        print('[SAF] 授权失败: $e');
      }
      return SafAuthorizationResult.error('授权失败: $e');
    }
  }

  /// 检查指定日期的日志文件是否存在
  Future<bool> logFileExists(String fileName) async {
    final state = await getPermissionState();
    if (state != SafPermissionState.authorized) {
      return false;
    }

    try {
      final uri = Uri.parse(_cachedUriString!);
      final fileUri = await FlutterSaf.getFile(uri, fileName);
      return fileUri != null && await FlutterSaf.isFile(fileUri);
    } catch (e) {
      return false;
    }
  }

  /// 读取日志文件内容
  /// 返回文件行列表，如果文件不存在或读取失败返回空列表
  Future<List<String>> readLogFile(String fileName) async {
    final state = await getPermissionState();
    if (state != SafPermissionState.authorized) {
      return [];
    }

    try {
      final uri = Uri.parse(_cachedUriString!);
      final fileUri = await FlutterSaf.getFile(uri, fileName);
      if (fileUri == null || !await FlutterSaf.isFile(fileUri)) {
        return [];
      }

      final content = await FlutterSaf.readTextFile(fileUri);
      return content.split('\n');
    } catch (e) {
      if (kDebugMode) {
        print('[SAF] 读取文件失败: $e');
      }
      return [];
    }
  }

  /// 获取文件夹中的文件列表
  Future<List<String>> listFiles() async {
    final state = await getPermissionState();
    if (state != SafPermissionState.authorized) {
      return [];
    }

    try {
      final uri = Uri.parse(_cachedUriString!);
      final files = await FlutterSaf.listFiles(uri);
      return files.where((f) => f.isFile).map((f) => f.name).toList();
    } catch (e) {
      return [];
    }
  }

  /// 检查授权是否有效，如果失效则清除缓存
  Future<bool> validatePermission() async {
    final state = await getPermissionState();
    return state == SafPermissionState.authorized;
  }

  /// 清除授权缓存
  void _clearCache() {
    _cachedUriString = null;
    _saveUri(null);
  }

  /// 保存 URI 到 SharedPreferences
  Future<void> _saveUri(String? uriString) async {
    final prefs = await SharedPreferences.getInstance();
    if (uriString != null && uriString.isNotEmpty) {
      await prefs.setString(_prefKeySafUri, uriString);
    } else {
      await prefs.remove(_prefKeySafUri);
    }
  }

  /// 获取缓存的 URI（用于调试）
  String? get cachedUri => _cachedUriString;
}