One-off event for snackbar message

OneOffEventForSnackbar.kt

// ---- User side (Write every time) ----

  val scaffoldState = rememberScaffoldState()
  val viewModel = hiltViewModel<FooViewModel>()
  SnackbarMessageEffect(
      scaffoldState = scaffoldState,
      messageStateHolder = viewModel
  )
  Scaffold(scaffoldState = scaffoldState) {
  ...
  }
  
@HiltViewModel
class FooViewModel @Inject constructor(
    private val repository: Repository,
    private val messageStateHolder: MessageStateHolder,
) :
    ViewModel(),
    MessageStateHolder by messageStateHolder {
    fun bar() {
      try {
      }catch (..) {
        addMessage("error!!")
      }
    }
}      
      
// ---- Library side(Write only once) ----

@Composable
fun SnackbarMessageEffect(
    scaffoldState: ScaffoldState,
    messageStateHolder: MessageStateHolder
) {
    messageStateHolder.messageUiState.userMessages.firstOrNull()?.let { userMessage ->
        LaunchedEffect(userMessage) {
            scaffoldState.snackbarHostState.showSnackbar(userMessage.message)
            messageStateHolder.userMessageShown(userMessage.id)
        }
    }
}

data class UserMessage(val id: Long, val message: String)

data class MessageUiState(
    val userMessages: List<UserMessage> = emptyList()
)

@Module
@InstallIn(ViewModelComponent::class)
class MessageStateHolderModule{
    @Provides
    fun provideMessageStateHolder(): MessageStateHolder {
        return MessageStateHolderImpl()
    }
}

class MessageStateHolderImpl : MessageStateHolder {
    private var _messageUiState by mutableStateOf(MessageUiState())
    override val messageUiState get() = _messageUiState
    override fun userMessageShown(messageId: Long) {
        val messages = _messageUiState.userMessages.filterNot { it.id == messageId }
        _messageUiState = _messageUiState.copy(userMessages = messages)
    }

    override fun addMessage(message: String) {
        val messages = _messageUiState.userMessages + UserMessage(
            id = UUID.randomUUID().mostSignificantBits,
            message = message
        )
        _messageUiState = _messageUiState.copy(userMessages = messages)
    }
}

interface MessageStateHolder {
    val messageUiState: MessageUiState
    fun userMessageShown(messageId: Long)
    fun addMessage(message: String)
}