import 'dart:convert';

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

import '../models/tracker.dart';

/// Persists the list of trackers to [SharedPreferences] as JSON.
///
/// A repository is justified here because storage is asynchronous, has
/// specialized queries (save/load all), and is consumed both by the service
/// layer and by tests with fake implementations.
class TrackerStorage {
  TrackerStorage(this._prefs);

  static const String _storageKey = 'bible_tracker.trackers.v1';

  final SharedPreferences _prefs;

  /// Synchronous because the underlying [SharedPreferences] getter already
  /// works against an in-memory cache. Keeping this sync lets the service
  /// start up with real data on the first frame, with no async-load race.
  List<Tracker> loadAll() {
    final String? raw = _prefs.getString(_storageKey);
    if (raw == null || raw.isEmpty) {
      return <Tracker>[];
    }
    final List<dynamic> decoded = jsonDecode(raw) as List<dynamic>;
    return decoded
        .cast<Map<String, dynamic>>()
        .map(Tracker.fromJson)
        .toList(growable: false);
  }

  Future<void> saveAll(List<Tracker> trackers) async {
    final List<Map<String, dynamic>> json = trackers
        .map((Tracker tracker) => tracker.toJson())
        .toList(growable: false);
    await _prefs.setString(_storageKey, jsonEncode(json));
  }
}

/// Must be overridden at startup with an initialized [SharedPreferences].
final Provider<SharedPreferences> sharedPreferencesProvider =
    Provider<SharedPreferences>(
      (Ref ref) => throw UnimplementedError(
        'sharedPreferencesProvider must be overridden before use',
      ),
    );

final Provider<TrackerStorage> trackerStorageProvider =
    Provider<TrackerStorage>(
      (Ref ref) => TrackerStorage(ref.read(sharedPreferencesProvider)),
    );