[Android] 035. イベント消費型UIイベント(StateFlow)

@Stable
sealed class Event {
    val id = UUID.randomUUID().toString()
    data class Message(val message: String) : Event()
}

class AppViewModel : ViewModel() {
    private val _uiEvents = MutableStateFlow<List<Event>>(emptyList())
    val uiEvents = _uiEvents.asStateFlow()

    fun stub() = viewModelScope.launch {
        val message = listOf(
            "おはよう",
            "こんにちわ",
            "こんばんわ",
        )

        repeat(5) {
            val msg = message.random()
            _uiEvents.update {
                it + Event.Message(msg)
            }
        }
    }

    fun consumeEvent(event: Event) {
        _uiEvents.update {
            e -> e.filterNot { it.id == event.id }
        }
    }
}

@Composable
fun AppContent(viewModel: AppViewModel = viewModel()) {
    val uiEvents by viewModel.uiEvents.collectAsState()
    var message by remember { mutableStateOf("") }

    LaunchedEffect(uiEvents) {
        if (uiEvents.isNotEmpty()) {
            when (val event = uiEvents.first()) {
                is Event.Message -> {
                    message = "${event.message}(${event.id})"
                    Log.d("App", message)
                    launch {
                        delay(1_000)
                        viewModel.consumeEvent(event)
                    }
                }
            }
        }
    }

    Column {
        Button(onClick = { viewModel.stub() }) {
            Text("Start")
        }
        Text(message)
    }
}