Override flutterflows in-app chat

Future sendChatMessage(
  DocumentReference hostRef,
  DocumentReference userRef,
  String message,
) async {
  var chatsCollection = FirebaseFirestore.instance.collection('chats');

  // Check if a chat already exists between the two users.
  var existingChatUserA =
      await chatsCollection.where('user_a', whereIn: [hostRef, userRef]).get();

  var existingChatUserB =
      await chatsCollection.where('user_b', whereIn: [hostRef, userRef]).get();

  var existingChat = [...existingChatUserA.docs, ...existingChatUserB.docs];

  DocumentReference chatRef;

  if (existingChat.isNotEmpty) {
    // If a chat already exists, use the existing chat.
    chatRef = existingChat.first.reference;
  } else {
    // If a chat does not exist, create a new chat.
    var newChatData = {
      'users': [hostRef, userRef],
      'user_a': userRef,
      'user_b': hostRef,
      'last_message': message,
      'last_message_time': DateTime.now(),
      'last_message_sent_by': userRef,
      'last_message_seen_by': [userRef],
    };

    chatRef = await chatsCollection.add(newChatData);
  }

  // Create a new chat message in the 'chat_messages' collection.
  var chatMessagesCollection =
      FirebaseFirestore.instance.collection('chat_messages');
  var newMessageData = {
    'chat': chatRef,
    'text': message,
    'user': userRef,
    'timestamp': DateTime.now(),
  };
  await chatMessagesCollection.add(newMessageData);

  // Update the chatRef with the lastMessage and lastMessageSentBy fields
  await chatRef.update({
    'lastMessage': message,
    'lastMessageSentBy': userRef,
  });
}