import 'dart:convert';

import 'package:shared_preferences/shared_preferences.dart';

import 'saved_place.dart';

/// Stores saved places on the device.
///
/// Local storage, and only local storage. A saved place is the closest thing
/// this app has to a home address; it never reaches a server, which is what
/// lets the Data safety declaration say that no location is collected. See
/// docs/privacy.md.
abstract interface class PlacesStore {
  Future<List<SavedPlace>> load();

  Future<void> save(List<SavedPlace> places);
}

class SharedPreferencesPlacesStore implements PlacesStore {
  const SharedPreferencesPlacesStore();

  static const String storageKey = 'nuvolari.saved_places.v1';

  @override
  Future<List<SavedPlace>> load() async {
    final prefs = await SharedPreferences.getInstance();
    final raw = prefs.getString(storageKey);
    if (raw == null || raw.isEmpty) return const <SavedPlace>[];

    try {
      final decoded = jsonDecode(raw);
      if (decoded is! List) return const <SavedPlace>[];
      return decoded
          .whereType<Map<String, Object?>>()
          .map(SavedPlace.fromJson)
          .toList(growable: false);
    } on Object {
      // Corrupt storage loses the places, which is bad, but throwing here would
      // make the app unopenable, which is worse. Starting empty is recoverable
      // by the user; a crash loop is not.
      return const <SavedPlace>[];
    }
  }

  @override
  Future<void> save(List<SavedPlace> places) async {
    final prefs = await SharedPreferences.getInstance();
    await prefs.setString(
      storageKey,
      jsonEncode(places.map((place) => place.toJson()).toList(growable: false)),
    );
  }
}

/// An in-memory store, for tests and for previewing without touching the device.
class InMemoryPlacesStore implements PlacesStore {
  InMemoryPlacesStore([List<SavedPlace>? initial])
    : _places = List<SavedPlace>.of(initial ?? const <SavedPlace>[]);

  List<SavedPlace> _places;

  @override
  Future<List<SavedPlace>> load() async =>
      List<SavedPlace>.unmodifiable(_places);

  @override
  Future<void> save(List<SavedPlace> places) async {
    _places = List<SavedPlace>.of(places);
  }
}