fetchMoreMessage method

Implementation

@override
Future<void> fetchMoreMessage(
  int pageSize,
  String chatId,
) async {
  if (lastChat != chatId) {
    _cumulativeMessages = [];
    lastChat = chatId;
    lastMessage = null;
  }

  // get the x amount of last messages from the oldest message that is in
  // cumulative messages and add that to the list
  var messages = <ChatMessageModel>[];
  QuerySnapshot<FirebaseMessageDocument>? messagesQuerySnapshot;
  var query = _db
      .collection(_options.chatsCollectionName)
      .doc(chatId)
      .collection(_options.messagesCollectionName)
      .orderBy('timestamp', descending: true)
      .limit(pageSize);
  if (lastMessage == null) {
    messagesQuerySnapshot = await query
        .withConverter<FirebaseMessageDocument>(
          fromFirestore: (snapshot, _) =>
              FirebaseMessageDocument.fromJson(snapshot.data()!, snapshot.id),
          toFirestore: (user, _) => user.toJson(),
        )
        .get();
    if (messagesQuerySnapshot.docs.isNotEmpty) {
      lastMessage = messagesQuerySnapshot.docs.last;
    }
  } else {
    messagesQuerySnapshot = await query
        .startAfterDocument(lastMessage!)
        .withConverter<FirebaseMessageDocument>(
          fromFirestore: (snapshot, _) =>
              FirebaseMessageDocument.fromJson(snapshot.data()!, snapshot.id),
          toFirestore: (user, _) => user.toJson(),
        )
        .get();
    if (messagesQuerySnapshot.docs.isNotEmpty) {
      lastMessage = messagesQuerySnapshot.docs.last;
    }
  }

  var messageDocuments = messagesQuerySnapshot.docs
      .map((QueryDocumentSnapshot<FirebaseMessageDocument> doc) => doc.data())
      .toList();
  for (var message in messageDocuments) {
    var sender = await _userService.getUser(message.sender);
    if (sender != null) {
      var timestamp = DateTime.fromMillisecondsSinceEpoch(
        message.timestamp.millisecondsSinceEpoch,
      );

      messages.add(
        message.imageUrl != null
            ? ChatImageMessageModel(
                sender: sender,
                imageUrl: message.imageUrl!,
                timestamp: timestamp,
              )
            : ChatTextMessageModel(
                sender: sender,
                text: message.text!,
                timestamp: timestamp,
              ),
      );
    }
  }

  _cumulativeMessages = [
    ...messages,
    ..._cumulativeMessages,
  ];
  _cumulativeMessages.sort((a, b) => a.timestamp.compareTo(b.timestamp));
  notifyListeners();
}