Challenge 3: A Settings ViewModel — Solution

@HiltViewModel
class SettingsViewModel @Inject constructor(
    private val repository: SettingsRepository
) : ViewModel() {

    val notificationsEnabled: StateFlow<Boolean> = repository.notificationsEnabled
        .stateIn(
            scope = viewModelScope,
            started = SharingStarted.WhileSubscribed(5000),
            initialValue = true
        )

    fun toggleNotifications() {
        viewModelScope.launch {
            val current = notificationsEnabled.value
            repository.setNotificationsEnabled(!current)
        }
    }
}

// In a composable
@Composable
fun SettingsScreen(viewModel: SettingsViewModel = hiltViewModel()) {
    val notificationsEnabled by viewModel.notificationsEnabled.collectAsStateWithLifecycle()

    Row {
        Text("Notifications")
        Switch(
            checked = notificationsEnabled,
            onCheckedChange = { viewModel.toggleNotifications() }
        )
    }
}

Notes:
- notificationsEnabled.value inside toggleNotifications() reads the
  StateFlow's CURRENT value directly (StateFlow always has one, per
  Kotlin Intermediate Chapter 2) — no need to collect it separately just
  to read the latest value for the toggle logic.
- !current inverts the boolean, and repository.setNotificationsEnabled(!current)
  writes it back through the repository, which itself writes it into
  DataStore — the UI never touches DataStore directly at any point in
  this chain.
- This ViewModel follows the exact same shape as every other
  @HiltViewModel in this course: a repository injected via constructor,
  a Flow converted to StateFlow via stateIn, and viewModelScope.launch
  wrapping any suspend write — DataStore is simply the newest data
  source slotted into an already-established pattern.