import 'dart:async';
import 'dart:convert';

import 'package:flutter_secure_storage/flutter_secure_storage.dart';
import 'package:http/http.dart' as http;
import 'package:matrix/matrix.dart';
import 'package:unifiedpush/unifiedpush.dart';

import 'notifications.dart';

/// Push notifications through UnifiedPush.
///
/// The user picks a distributor app (ntfy, or another UnifiedPush
/// distributor) which gives this app an endpoint URL. The endpoint becomes a
/// Matrix pusher: the homeserver posts each notification to the
/// distributor's Matrix gateway, the distributor wakes the app, and the app
/// fetches the event (decrypting it if it can) and shows it.
///
/// Pushes are `event_id_only`, so neither the gateway nor the distributor
/// sees message content, not even in unencrypted rooms.
///
/// No Google services are involved, so this works without a Firebase
/// project; the cost is that the user needs a distributor installed.
class Push {
  Push._();

  static const appId = 'io.github.dariuszjaniak.warp';
  static const _endpointKey = 'warp.push.endpoint';
  static const _storage = FlutterSecureStorage();

  /// Where a push goes when the distributor's server has no Matrix gateway
  /// of its own: the UnifiedPush project's public one, which forwards to any
  /// endpoint.
  static const fallbackGateway =
      'https://matrix.gateway.unifiedpush.org/_matrix/push/v1/notify';

  static Client? _client;

  /// Sets up the push receiver. Called on every start, in the foreground and
  /// when a push starts the app in the background.
  static Future<void> init(Client client) async {
    _client = client;
    final registered = await UnifiedPush.initialize(
      onNewEndpoint: (endpoint, _) => _onNewEndpoint(endpoint.url),
      onUnregistered: (_) => _onUnregistered(),
      onRegistrationFailed: (reason, _) =>
          Logs().w('UnifiedPush registration failed: $reason'),
      onMessage: (message, _) => _onMessage(message),
    );
    // The connector wants a register() on every start to keep its
    // registration with the distributor alive.
    if (registered && client.isLogged()) {
      await UnifiedPush.register(features: const []);
    }
  }

  /// The installed distributors, by package name.
  static Future<List<String>> distributors() => UnifiedPush.getDistributors();

  static Future<String?> currentDistributor() => UnifiedPush.getDistributor();

  /// Turns push on with [distributor], or the default one when null. Returns
  /// false when there is no distributor to use and the user has to pick one.
  static Future<bool> enable({String? distributor}) async {
    if (distributor != null) {
      await UnifiedPush.saveDistributor(distributor);
    } else if (!await UnifiedPush.tryUseCurrentOrDefaultDistributor()) {
      return false;
    }
    await UnifiedPush.register(features: const []);
    return true;
  }

  /// Turns push off: unregisters from the distributor and removes the
  /// pusher from the homeserver.
  static Future<void> disable() async {
    await UnifiedPush.unregister();
    await _onUnregistered();
  }

  /// Removes this device's pusher, when signing out. The homeserver also
  /// removes it when the session ends, so this is best effort.
  static Future<void> forget() async {
    try {
      await UnifiedPush.unregister();
    } catch (_) {}
    await _storage.delete(key: _endpointKey);
  }

  static Future<void> _onNewEndpoint(String endpoint) async {
    final client = _client;
    if (client == null || !client.isLogged()) return;
    final previous = await _storage.read(key: _endpointKey);
    if (previous != null && previous != endpoint) {
      await _deletePusher(client, previous);
    }
    final gateway = await _gatewayFor(endpoint);
    await client.postPusher(
      Pusher(
        appId: appId,
        pushkey: endpoint,
        appDisplayName: 'Warp',
        deviceDisplayName: client.deviceName ?? 'Warp Android',
        kind: 'http',
        lang: 'en',
        data: PusherData(url: Uri.parse(gateway), format: 'event_id_only'),
      ),
      append: false,
    );
    await _storage.write(key: _endpointKey, value: endpoint);
    Logs().i('Pusher registered with gateway $gateway');
  }

  static Future<void> _onUnregistered() async {
    final client = _client;
    final endpoint = await _storage.read(key: _endpointKey);
    if (client != null && endpoint != null && client.isLogged()) {
      await _deletePusher(client, endpoint);
    }
    await _storage.delete(key: _endpointKey);
  }

  static Future<void> _deletePusher(Client client, String endpoint) async {
    try {
      await client.deletePusher(PusherId(appId: appId, pushkey: endpoint));
    } catch (e) {
      Logs().w('Could not remove the old pusher', e);
    }
  }

  /// The Matrix gateway for [endpoint]. UnifiedPush's discovery: a server
  /// that has one answers `GET /_matrix/push/v1/notify` with
  /// `{"unifiedpush": {"gateway": "matrix"}}`.
  static Future<String> _gatewayFor(String endpoint) async {
    final uri = Uri.parse(endpoint);
    final candidate = uri.replace(
      path: '/_matrix/push/v1/notify',
      query: null,
      fragment: null,
    );
    try {
      final response = await http
          .get(candidate)
          .timeout(const Duration(seconds: 10));
      if (response.statusCode == 200) {
        final json = jsonDecode(response.body);
        if (json is Map &&
            json['unifiedpush'] is Map &&
            json['unifiedpush']['gateway'] == 'matrix') {
          return candidate.toString();
        }
      }
    } catch (e) {
      Logs().v('No Matrix gateway at ${candidate.origin}', e);
    }
    return fallbackGateway;
  }

  static Future<void> _onMessage(PushMessage message) async {
    final client = _client;
    Map<String, Object?> notification;
    try {
      final json = jsonDecode(utf8.decode(message.content));
      notification = Map<String, Object?>.from(
        (json is Map && json['notification'] is Map)
            ? json['notification'] as Map
            : json as Map,
      );
    } catch (e) {
      Logs().w('Push that is not a Matrix notification', e);
      return;
    }

    final push = PushNotification.fromJson(notification);
    final roomId = push.roomId;
    // A push with no event is the homeserver saying the counts changed:
    // everything was read on another device.
    if (push.eventId == null || roomId == null) {
      if ((push.counts?.unread ?? 0) == 0) await Notifications.clearAll();
      return;
    }
    if (client == null) return;

    try {
      // Null when the event has already been seen (read on another device,
      // or shown from the sync while the app was running).
      final event = await client.getEventByPushNotification(push);
      if (event != null) await Notifications.showEvent(event);
      return;
    } catch (e, s) {
      Logs().w('Could not fetch the pushed event', e, s);
    }
    // Fetching failed (no network, or the session is gone): still say
    // something arrived, without content.
    final room = client.getRoomById(roomId);
    await Notifications.show(
      roomId: roomId,
      title:
          room?.getLocalizedDisplayname() ??
          push.roomName ??
          push.senderDisplayName ??
          'Warp',
      body: 'New message',
    );
  }
}