PostsRepository.kt

fun addPost(post: Post) = flow<State<DocumentReference>> {

    // Emit loading state
    emit(State.loading())

    val postRef = mPostsCollection.add(post).await()

    // Emit success state with post reference
    emit(State.success(postRef))

}.catch {
    // If exception is thrown, emit failed state along with message.
    emit(State.failed(it.message.toString()))
}.flowOn(Dispatchers.IO)