Address Gemini code review feedback

- Move toNightMode() extension to core:ui module to eliminate code duplication
- Refactor MainActivity flow logic to use filterIsInstance<Success>() for better readability
- Remove duplicate DarkThemeConfigExt.kt files from app and feature:settings modules
- Update imports in MainActivity and SettingsViewModel

app/src/main/kotlin/com/google/samples/apps/nowinandroid/MainActivity.kt

@@ -43,13 +43,14 @@ import com.google.samples.apps.nowinandroid.core.data.util.NetworkMonitor
 import com.google.samples.apps.nowinandroid.core.data.util.TimeZoneMonitor
 import com.google.samples.apps.nowinandroid.core.designsystem.theme.NiaTheme
 import com.google.samples.apps.nowinandroid.core.ui.LocalTimeZone
+import com.google.samples.apps.nowinandroid.core.ui.toNightMode
 import com.google.samples.apps.nowinandroid.ui.NiaApp
 import com.google.samples.apps.nowinandroid.ui.rememberNiaAppState
 import com.google.samples.apps.nowinandroid.util.isSystemInDarkTheme
-import com.google.samples.apps.nowinandroid.util.toNightMode
 import dagger.hilt.android.AndroidEntryPoint
 import kotlinx.coroutines.flow.combine
 import kotlinx.coroutines.flow.distinctUntilChanged
+import kotlinx.coroutines.flow.filterIsInstance
 import kotlinx.coroutines.flow.map
 import kotlinx.coroutines.flow.onEach
 import kotlinx.coroutines.launch
@@ -86,14 +87,9 @@ class MainActivity : ComponentActivity() {
         // uses the correct theme. This addresses issue #633.
         lifecycleScope.launch {
             viewModel.uiState
-                .map { state ->
-                    if (state is Success) {
-                        state.userData.darkThemeConfig.toNightMode()
-                    } else {
-                        null
-                    }
-                }
-                .first { it != null } // Only take the first non-null mode
+                .filterIsInstance<Success>()
+                .map { it.userData.darkThemeConfig.toNightMode() }
+                .first()
                 .let { mode ->
                     AppCompatDelegate.setDefaultNightMode(mode)
                 }

core/ui/src/main/kotlin/com/google/samples/apps/nowinandroid/core/ui/DarkThemeConfigExt.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2022 The Android Open Source Project
+ * Copyright 2026 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -14,14 +14,13 @@
  * limitations under the License.
  */
 
-package com.google.samples.apps.nowinandroid.util
+package com.google.samples.apps.nowinandroid.core.ui
 
 import androidx.appcompat.app.AppCompatDelegate
 import com.google.samples.apps.nowinandroid.core.model.data.DarkThemeConfig
 
 /**
- * Converts [DarkThemeConfig] to the corresponding [AppCompatDelegate] night mode constant.
- * This is used to set the application-level night mode for the splash screen and system UI.
+ * Converts [DarkThemeConfig] to [AppCompatDelegate] night mode constant.
  */
 fun DarkThemeConfig.toNightMode(): Int = when (this) {
     DarkThemeConfig.FOLLOW_SYSTEM -> AppCompatDelegate.MODE_NIGHT_FOLLOW_SYSTEM

feature/settings/impl/src/main/kotlin/com/google/samples/apps/nowinandroid/feature/settings/impl/DarkThemeConfigExt.kt

@@ -1,30 +0,0 @@
-/*
- * Copyright 2022 The Android Open Source Project
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     https://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package com.google.samples.apps.nowinandroid.feature.settings.impl
-
-import androidx.appcompat.app.AppCompatDelegate
-import com.google.samples.apps.nowinandroid.core.model.data.DarkThemeConfig
-
-/**
- * Converts [DarkThemeConfig] to the corresponding [AppCompatDelegate] night mode constant.
- * This is used to set the application-level night mode for the splash screen and system UI.
- */
-internal fun DarkThemeConfig.toNightMode(): Int = when (this) {
-    DarkThemeConfig.FOLLOW_SYSTEM -> AppCompatDelegate.MODE_NIGHT_FOLLOW_SYSTEM
-    DarkThemeConfig.LIGHT -> AppCompatDelegate.MODE_NIGHT_NO
-    DarkThemeConfig.DARK -> AppCompatDelegate.MODE_NIGHT_YES
-}

feature/settings/impl/src/main/kotlin/com/google/samples/apps/nowinandroid/feature/settings/impl/SettingsViewModel.kt

@@ -22,6 +22,7 @@ import androidx.lifecycle.viewModelScope
 import com.google.samples.apps.nowinandroid.core.data.repository.UserDataRepository
 import com.google.samples.apps.nowinandroid.core.model.data.DarkThemeConfig
 import com.google.samples.apps.nowinandroid.core.model.data.ThemeBrand
+import com.google.samples.apps.nowinandroid.core.ui.toNightMode
 import com.google.samples.apps.nowinandroid.feature.settings.impl.SettingsUiState.Loading
 import com.google.samples.apps.nowinandroid.feature.settings.impl.SettingsUiState.Success
 import dagger.hilt.android.lifecycle.HiltViewModel