fetchPostsPaginated method

Implementation

@override
Future<List<TimelinePost>> fetchPostsPaginated(
  String? category,
  int limit,
) async {
  // only take posts that are in our category
  var oldestPost = posts
      .where(
        (element) => category == null || element.category == category,
      )
      .fold(
        posts.first,
        (previousValue, element) =>
            (previousValue.createdAt.isBefore(element.createdAt))
                ? previousValue
                : element,
      );
  var snapshot = (category != null)
      ? await _db
          .collection(_options.timelineCollectionName)
          .where('category', isEqualTo: category)
          .orderBy('created_at', descending: true)
          .startAfter([oldestPost])
          .limit(limit)
          .get()
      : await _db
          .collection(_options.timelineCollectionName)
          .orderBy('created_at', descending: true)
          .startAfter([oldestPost.createdAt])
          .limit(limit)
          .get();
  // add the new posts to the list
  var newPosts = <TimelinePost>[];
  for (var doc in snapshot.docs) {
    var data = doc.data();
    var user = await _userService.getUser(data['creator_id']);
    var post = TimelinePost.fromJson(doc.id, data).copyWith(creator: user);
    newPosts.add(post);
  }
  posts = [...posts, ...newPosts];
  notifyListeners();
  return newPosts;
}