Challenge 1: A Preferences DataStore Setting — Solution

val Context.dataStore: DataStore<Preferences> by preferencesDataStore(name = "app_settings")

object PreferencesKeys {
    val NOTIFICATIONS_ENABLED = booleanPreferencesKey("notifications_enabled")
}

fun getNotificationsEnabled(context: Context): Flow<Boolean> =
    context.dataStore.data.map { prefs ->
        prefs[PreferencesKeys.NOTIFICATIONS_ENABLED] ?: true
    }

suspend fun setNotificationsEnabled(context: Context, enabled: Boolean) {
    context.dataStore.edit { prefs ->
        prefs[PreferencesKeys.NOTIFICATIONS_ENABLED] = enabled
    }
}

Notes:
- prefs[PreferencesKeys.NOTIFICATIONS_ENABLED] ?: true uses the Elvis
  operator (Kotlin Fundamentals Chapter 3) — since the key genuinely
  might not exist yet (e.g. the very first time the app runs before any
  write has happened), the fallback default (true, meaning notifications
  are on by default) covers that case cleanly.
- context.dataStore.data is a Flow<Preferences> — .map { } transforms it
  into a Flow<Boolean> focused on just this one setting, using Kotlin
  Intermediate Chapter 2's Flow operators.
- setNotificationsEnabled is a suspend function, since dataStore.edit { }
  itself suspends — it can only be called from a coroutine, not directly
  from, say, a Button's onClick lambda without wrapping it in a launch.