MessagesViewModel.kt

private val messageMap = linkedMapOf<String, MessageItem>()

private fun updateMessagesMap(documents: List<DocumentChange>) {
	documents.forEach { documentChange ->
        val message = documentChange.document
			.toObject(MessageResponse::class.java)
        when (documentChange.type) {
            Type.ADDED -> {
                messageMap[message.id] = message
            }
            Type.MODIFIED -> {
                messageMap[message.id] = message
            }
            Type.REMOVED -> {
                messageMap.remove(message.id)
            }
       }
    }
}