import 'dart:convert';
import 'package:shared_preferences/shared_preferences.dart';

/// Base class for services that use SharedPreferences singleton pattern.
///
/// This class handles the boilerplate for singleton initialization and
/// SharedPreferences lifecycle management. Subclasses should:
/// 1. Create a private named constructor (e.g., SettingsService._())
/// 2. Implement their own getInstance() method that calls BaseSharedPreferencesService.initializeInstance()
/// 3. Optionally override onInit() for post-initialization setup
abstract class BaseSharedPreferencesService {
  static final Map<Type, BaseSharedPreferencesService> _instances = {};
  late SharedPreferences _prefs;

  /// Protected constructor for subclasses
  BaseSharedPreferencesService();

  /// Access to SharedPreferences instance
  SharedPreferences get prefs => _prefs;

  /// Initialize the SharedPreferences instance
  ///
  /// This method handles:
  /// - Singleton instance management
  /// - SharedPreferences initialization
  /// - Calling onInit() hook for subclass-specific setup
  static Future<T> initializeInstance<T extends BaseSharedPreferencesService>(T Function() constructor) async {
    if (_instances[T] == null) {
      final instance = constructor();
      _instances[T] = instance;
      instance._prefs = await SharedPreferences.getInstance();
      await instance.onInit();
    }
    return _instances[T] as T;
  }

  /// Decode a JSON string to a Map with error handling.
  ///
  /// If [legacyStringOk] is true and the value is a plain string (not valid
  /// JSON), returns `{'key': jsonString, 'descending': false}` for legacy
  /// library sort compatibility.
  Map<String, dynamic> decodeJsonStringToMap(String jsonString, {bool legacyStringOk = false}) {
    try {
      return json.decode(jsonString) as Map<String, dynamic>;
    } catch (e) {
      if (legacyStringOk) {
        return {'key': jsonString, 'descending': false};
      }
      return {};
    }
  }

  /// Hook for subclass-specific initialization after SharedPreferences is ready.
  ///
  /// Override this method to perform any setup that requires access to
  /// SharedPreferences (e.g., registering values with other services).
  Future<void> onInit() async {
    // Default implementation does nothing
  }
}