buzz/mobile/lib/features/profile/user_status_cache_provider.dart

import 'dart:async';

import 'package:flutter/foundation.dart';
import 'package:hooks_riverpod/hooks_riverpod.dart';

import '../../shared/relay/relay.dart';
import 'user_status.dart';

/// In-memory cache of other users' NIP-38 statuses (kind:30315, d=general).
///
/// Subscribes to kind:30315 events over WebSocket for real-time updates.
/// Falls back to a 120-second backstop refresh via fetchHistory.
class UserStatusCacheNotifier extends Notifier<Map<String, UserStatus?>> {
  static const _refreshInterval = Duration(seconds: 120);

  final Set<String> _tracked = {};
  final Set<String> _pending = {};
  Timer? _batchTimer;
  Timer? _refreshTimer;
  void Function()? _statusUnsub;
  int _subscriptionVersion = 0;

  @override
  Map<String, UserStatus?> build() {
    ref.watch(relayClientProvider);
    final sessionState = ref.watch(relaySessionProvider);

    ref.onDispose(() {
      _batchTimer?.cancel();
      _batchTimer = null;
      _refreshTimer?.cancel();
      _refreshTimer = null;
      _statusUnsub?.call();
      _statusUnsub = null;
    });

    if (sessionState.status == SessionStatus.connected) {
      _subscribeStatusUpdates();
    }

    return {};
  }

  /// Track status for [pubkeys]. Fetches immediately if not cached,
  /// and includes them in periodic refreshes.
  void track(List<String> pubkeys) {
    final normalized = pubkeys.map((pk) => pk.toLowerCase()).toList();
    final uncached = normalized
        .where((pk) => !state.containsKey(pk) && !_pending.contains(pk))
        .toList();

    _tracked.addAll(normalized);
    _ensureRefreshTimer();

    if (uncached.isEmpty) return;
    _pending.addAll(uncached);
    _batchTimer ??= Timer(const Duration(milliseconds: 50), _flushPending);
  }

  void _ensureRefreshTimer() {
    _refreshTimer ??= Timer.periodic(_refreshInterval, (_) => _refreshAll());
  }

  Future<void> _subscribeStatusUpdates() async {
    _statusUnsub?.call();
    _statusUnsub = null;
    _subscriptionVersion++;
    final version = _subscriptionVersion;

    final session = ref.read(relaySessionProvider.notifier);
    try {
      final unsub = await session.subscribe(
        const NostrFilter(
          kinds: [EventKind.userStatus],
          tags: {
            '#d': ['general'],
          },
          limit: 0,
        ),
        _handleStatusEvent,
      );
      if (version != _subscriptionVersion) {
        unsub();
        return;
      }
      _statusUnsub = unsub;
    } catch (error) {
      debugPrint(
        '[UserStatusCacheNotifier] status subscription failed: $error',
      );
    }
  }

  void _handleStatusEvent(NostrEvent event) {
    // Defense-in-depth: guard d-tag even though filter includes it.
    if (event.getTagValue('d') != 'general') return;

    final pubkey = event.pubkey.toLowerCase();
    if (!_tracked.contains(pubkey)) return;

    final parsed = UserStatus.fromEvent(event);
    final existing = state[pubkey];

    // Staleness guard: discard if we already have a newer-or-equal event.
    if (existing != null && existing.updatedAt >= parsed.updatedAt) return;

    final status = parsed.isEmpty ? null : parsed;
    final updated = Map<String, UserStatus?>.from(state);
    updated[pubkey] = status;
    state = updated;
  }

  /// Directly update a pubkey's cached status. Used by [UserStatusNotifier]
  /// for optimistic updates after publishing.
  void updateStatus(String pubkey, UserStatus? status) {
    final pk = pubkey.toLowerCase();
    final updated = Map<String, UserStatus?>.from(state);
    updated[pk] = status;
    state = updated;
  }

  Future<void> _refreshAll() async {
    if (_tracked.isEmpty) return;
    await _fetchStatuses(_tracked.toList());
  }

  Future<void> _flushPending() async {
    _batchTimer = null;
    if (_pending.isEmpty) return;

    final pubkeys = _pending.toList();
    _pending.clear();
    await _fetchStatuses(pubkeys);
  }

  Future<void> _fetchStatuses(List<String> pubkeys) async {
    try {
      final session = ref.read(relaySessionProvider.notifier);
      final events = await session.fetchHistory(
        NostrFilter(
          kinds: const [EventKind.userStatus],
          authors: pubkeys,
          tags: const {
            '#d': ['general'],
          },
          limit: pubkeys.length,
        ),
      );

      final updated = Map<String, UserStatus?>.from(state);

      // Initialise requested pubkeys that had no events to null (cleared).
      for (final pk in pubkeys) {
        if (!updated.containsKey(pk)) {
          updated[pk] = null;
        }
      }

      for (final event in events) {
        if (event.getTagValue('d') != 'general') continue;
        final pk = event.pubkey.toLowerCase();
        final parsed = UserStatus.fromEvent(event);
        final existing = updated[pk];
        if (existing != null && existing.updatedAt >= parsed.updatedAt) {
          continue;
        }
        updated[pk] = parsed.isEmpty ? null : parsed;
      }

      state = updated;
    } catch (_) {
      // Silently fail — backstop will retry.
    }
  }
}

final userStatusCacheProvider =
    NotifierProvider<UserStatusCacheNotifier, Map<String, UserStatus?>>(
      UserStatusCacheNotifier.new,
    );