import 'dart:async';
import 'dart:ui' show Color;

import 'package:flutter/foundation.dart';
import 'package:flutter_local_notifications/flutter_local_notifications.dart';
import 'package:matrix/matrix.dart';

/// System notifications for new messages: one per room, replaced as more
/// messages arrive, opening the room when tapped.
///
/// They come from two places. While the app runs, from the SDK's
/// [Client.onNotification] (events the user's push rules say notify). While
/// it doesn't, from a push ([Push]), which starts the app in the background
/// just long enough to fetch the event and show it.
class Notifications {
  Notifications._();

  static final _plugin = FlutterLocalNotificationsPlugin();
  static final _opened = StreamController<String>.broadcast();
  static bool _ready = false;

  /// Room IDs of notifications the user tapped while the app was running.
  static Stream<String> get opened => _opened.stream;

  /// The room the user is looking at, whose messages don't notify.
  static String? activeRoomId;

  /// Whether the app is in the foreground. Messages in rooms other than
  /// [activeRoomId] still notify then.
  static bool foreground = true;

  static const _channel = AndroidNotificationChannel(
    'messages',
    'Messages',
    description: 'New messages and invites',
    importance: Importance.high,
  );

  static Future<void> init() async {
    if (_ready) return;
    await _plugin.initialize(
      settings: const InitializationSettings(
        android: AndroidInitializationSettings('ic_notification'),
      ),
      onDidReceiveNotificationResponse: (response) {
        final roomId = response.payload;
        if (roomId != null && roomId.isNotEmpty) _opened.add(roomId);
      },
    );
    await _plugin
        .resolvePlatformSpecificImplementation<
          AndroidFlutterLocalNotificationsPlugin
        >()
        ?.createNotificationChannel(_channel);
    _ready = true;
  }

  /// The room of the notification that launched the app, if one did.
  static Future<String?> launchRoomId() async {
    final details = await _plugin.getNotificationAppLaunchDetails();
    if (details?.didNotificationLaunchApp != true) return null;
    return details?.notificationResponse?.payload;
  }

  /// Asks for the Android 13+ notification permission. Returns whether
  /// notifications may be shown.
  static Future<bool> requestPermission() async =>
      await _plugin
          .resolvePlatformSpecificImplementation<
            AndroidFlutterLocalNotificationsPlugin
          >()
          ?.requestNotificationsPermission() ??
      true;

  /// Shows [event] unless the user is looking at its room.
  static Future<void> showEvent(Event event) async {
    final room = event.room;
    if (foreground && room.id == activeRoomId) return;
    final i18n = const MatrixDefaultLocalizations();
    final body = room.membership == Membership.invite
        ? '${event.senderFromMemoryOrFallback.calcDisplayname()} invited you'
        : event.calcLocalizedBodyFallback(
            i18n,
            withSenderNamePrefix: !room.isDirectChat,
            hideReply: true,
            plaintextBody: false,
            removeMarkdown: true,
          );
    await show(
      roomId: room.id,
      title: room.getLocalizedDisplayname(i18n),
      body: body,
      timestamp: event.originServerTs,
    );
  }

  static Future<void> show({
    required String roomId,
    required String title,
    required String body,
    DateTime? timestamp,
  }) async {
    if (!_ready) await init();
    try {
      await _plugin.show(
        id: _idFor(roomId),
        title: title,
        body: body,
        payload: roomId,
        notificationDetails: NotificationDetails(
          android: AndroidNotificationDetails(
            _channel.id,
            _channel.name,
            channelDescription: _channel.description,
            importance: Importance.high,
            priority: Priority.high,
            category: AndroidNotificationCategory.message,
            when: timestamp?.millisecondsSinceEpoch,
            showWhen: timestamp != null,
            color: const Color(0xFF00A389),
            groupKey: 'messages',
          ),
        ),
      );
    } catch (e, s) {
      Logs().w('Could not show a notification', e, s);
    }
  }

  /// Removes the room's notification, when it has been read or opened.
  static Future<void> clearRoom(String roomId) async {
    if (!_ready) return;
    await _plugin.cancel(id: _idFor(roomId));
  }

  static Future<void> clearAll() async {
    if (!_ready) return;
    await _plugin.cancelAll();
  }

  // Notification IDs are 32-bit ints; a room's is a stable hash of its ID so
  // a new message replaces the room's previous notification.
  static int _idFor(String roomId) {
    var h = 0x811c9dc5;
    for (final unit in roomId.codeUnits) {
      h = ((h ^ unit) * 0x01000193) & 0x7fffffff;
    }
    return h;
  }

  /// Listens to [client] for events that notify while the app is running.
  static StreamSubscription<Event> watch(Client client) =>
      client.onNotification.stream.listen((event) {
        if (kDebugMode) debugPrint('notify ${event.eventId}');
        showEvent(event);
      });
}