import 'dart:convert';

import 'package:flutter_secure_storage/flutter_secure_storage.dart';

/// Local persistence of story content-uuids the user has already viewed.
/// Backend's `isRead` may lag or reset on next fetch; this cache guarantees
/// the ring turns grey right after viewing and stays grey across refetches.
class StoryReadCache {
  StoryReadCache._();
  static final StoryReadCache instance = StoryReadCache._();

  static const String _key = 'story_read_uuids';
  static const int _maxEntries = 500;
  static const FlutterSecureStorage _storage = FlutterSecureStorage();

  final Set<String> _memory = <String>{};
  bool _hydrated = false;

  Future<void> hydrate() async {
    if (_hydrated) return;
    try {
      final raw = await _storage.read(key: _key);
      if (raw != null && raw.isNotEmpty) {
        final decoded = jsonDecode(raw);
        if (decoded is List) {
          _memory.addAll(decoded.whereType<String>());
        }
      }
    } catch (_) {}
    _hydrated = true;
  }

  bool contains(String? uuid) {
    if (uuid == null || uuid.isEmpty) return false;
    return _memory.contains(uuid);
  }

  Future<void> add(String? uuid) async {
    if (uuid == null || uuid.isEmpty) return;
    if (!_memory.add(uuid)) return;
    if (_memory.length > _maxEntries) {
      final excess = _memory.length - _maxEntries;
      final toRemove = _memory.take(excess).toList();
      _memory.removeAll(toRemove);
    }
    try {
      await _storage.write(key: _key, value: jsonEncode(_memory.toList()));
    } catch (_) {}
  }

  Future<void> clear() async {
    _memory.clear();
    try {
      await _storage.delete(key: _key);
    } catch (_) {}
  }
}