import 'dart:async';

import 'package:commons_core/commons_core.dart';
import 'package:connectivity_plus/connectivity_plus.dart';
import 'package:flutter/foundation.dart';

import 'message_store.dart';
import 'profile_cache.dart';
import 'social_service.dart';
import 'social_settings.dart';

/// App-wide inbox listener for private messages (NIP-17).
///
/// Without this, a message only arrived while its specific chat screen was
/// open — so a first message from a new peer was invisible (nothing in local
/// storage, so nothing in the inbox list, so you never opened the chat, so you
/// never subscribed). This keeps ONE long-lived subscription for the whole app
/// while online: it persists every incoming message to the [MessageStore] and
/// fires [changes] so the inbox list refreshes. Reconnects when the network
/// returns; degrades to nothing offline (local-first).
///
/// Foreground only — background/push delivery is a later concern.
class InboxService {
  InboxService({
    required SocialService social,
    required SocialSettings settings,
    required MessageStore store,
    ProfileCache? profileCache,
  })  : _social = social,
        _settings = settings,
        _store = store,
        _profileCache = profileCache;

  final SocialService _social;
  final SocialSettings _settings;
  final MessageStore _store;
  final ProfileCache? _profileCache;

  final _changes = StreamController<void>.broadcast();
  SocialSession? _session;
  StreamSubscription<PrivateMessage>? _inboxSub;
  StreamSubscription<List<ConnectivityResult>>? _connSub;
  bool _started = false;
  bool _connecting = false;

  /// Fires (with no payload) after a NEW message is persisted — the inbox list
  /// listens to this to reload. Broadcast, so several screens can listen.
  Stream<void> get changes => _changes.stream;

  /// Begins listening. Idempotent. Connects now if online, and (re)connects
  /// whenever the network returns. Safe to call once at app start.
  Future<void> start() async {
    if (_started) return;
    _started = true;
    try {
      _connSub = Connectivity().onConnectivityChanged.listen((results) {
        final offline =
            results.isEmpty || results.every((r) => r == ConnectivityResult.none);
        if (offline) {
          _dropSession();
        } else {
          unawaited(_connect());
        }
      });
    } catch (_) {
      // Platform without connectivity support — just try once below.
    }
    await _connect();
  }

  /// Opens a session and subscribes to the inbox, if not already connected.
  /// Guarded so overlapping connectivity events can't open two sessions.
  Future<void> _connect() async {
    if (_session != null || _connecting) return; // already (being) connected
    _connecting = true;
    try {
      final relays = await _settings.relayUrls();
      if (relays.isEmpty) return; // offline / unconfigured
      final session = await _social.openSession(relays);
      if (!_started) {
        await session.close(); // stopped while connecting
        return;
      }
      _session = session;
      _inboxSub = session.messages.inbox().listen(
        ingest,
        onError: (_) => _dropSession(), // relay dropped — retry on next change
      );
    } catch (_) {
      // No relay reachable — a later connectivity change retries.
    } finally {
      _connecting = false;
    }
  }

  /// Persists one incoming [message] (deduped) and, when it's new, fires
  /// [changes] and best-effort caches the sender's display name. Separated from
  /// the transport so it can be unit-tested without a relay.
  @visibleForTesting
  Future<void> ingest(PrivateMessage message) async {
    final stored = await _store.append(message.fromPubkey, message);
    if (!stored) return; // a re-delivered duplicate
    if (!_changes.isClosed) _changes.add(null);
    await _cacheName(message.fromPubkey);
  }

  Future<void> _cacheName(String peerPubkey) async {
    final cache = _profileCache;
    final session = _session;
    if (cache == null || session == null) return;
    if (await cache.name(peerPubkey) != null) return; // already known
    try {
      final profile = await session.profile.fetch(peerPubkey);
      if (profile != null && profile.name.isNotEmpty) {
        await cache.setName(peerPubkey, profile.name);
        if (!_changes.isClosed) _changes.add(null); // re-render with the name
      }
    } catch (_) {
      // best effort — the short key shows meanwhile
    }
  }

  void _dropSession() {
    unawaited(_inboxSub?.cancel());
    _inboxSub = null;
    unawaited(_session?.close());
    _session = null;
  }

  Future<void> stop() async {
    _started = false;
    await _connSub?.cancel();
    _connSub = null;
    await _inboxSub?.cancel();
    _inboxSub = null;
    await _session?.close();
    _session = null;
    if (!_changes.isClosed) await _changes.close();
  }
}