Refactor NavigationState and make tests pass

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

@@ -1,62 +0,0 @@
-/*
- * Copyright 2025 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.di
-
-// TODO: Rename to `NiaNavigationStateProvider`
-//  Does this even need to be injected? Can't we just instantiate it directly using `rememberNavigationState`?
-/*
-@Module
-@InstallIn(SingletonComponent::class)
-object NavigationStateProvider {
-    @Provides
-    @Singleton
-    fun provideNavigationState(): NiaNavigationState =
-        NiaNavigationState(
-            //startKey = TopLevelDestination.FOR_YOU.key,
-            startKey = object : NiaNavKey {
-                override val isTopLevel: Boolean
-                    get() = true
-            }
-        )
-
-// TODO: Remove commented out code
-//
-//    @Provides
-//    @Singleton
-//    fun provideNiaNavigator(
-//        state: NiaNavigatorState
-//    ): NiaNavigator =
-//        NiaNavigator(state)
-
-    */
-/**
-     * Registers feature modules' polymorphic serializers to support
-     * feature keys' save and restore by savedstate
-     * in [com.google.samples.apps.nowinandroid.core.navigation.NiaBackStackViewModel].
-     *//*
-
-    @Provides
-    @Singleton
-    fun provideSerializersModule(
-        polymorphicModuleBuilders: Set<@JvmSuppressWildcards PolymorphicModuleBuilder<NiaNavKey>.() -> Unit>,
-    ): SerializersModule = SerializersModule {
-        polymorphic(NiaNavKey::class) {
-            polymorphicModuleBuilders.forEach { it() }
-        }
-    }
-}
-*/

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

@@ -1,135 +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.navigation
-
-import androidx.annotation.StringRes
-import androidx.compose.ui.graphics.vector.ImageVector
-import androidx.navigation3.runtime.NavKey
-import com.google.samples.apps.nowinandroid.R
-import com.google.samples.apps.nowinandroid.core.designsystem.icon.NiaIcons
-import com.google.samples.apps.nowinandroid.feature.bookmarks.api.navigation.BookmarksRoute
-import com.google.samples.apps.nowinandroid.feature.foryou.api.navigation.ForYouRoute
-import com.google.samples.apps.nowinandroid.feature.interests.api.navigation.InterestsRoute
-import kotlin.reflect.KClass
-import com.google.samples.apps.nowinandroid.feature.bookmarks.api.R as bookmarksR
-import com.google.samples.apps.nowinandroid.feature.foryou.api.R as forYouR
-import com.google.samples.apps.nowinandroid.feature.search.api.R as searchR
-
-/**
- * Type for the top level destinations in the application. Contains metadata about the destination
- * that is used in the top app bar and common navigation UI.
- *
- * @param selectedIcon The icon to be displayed in the navigation UI when this destination is
- * selected.
- * @param unselectedIcon The icon to be displayed in the navigation UI when this destination is
- * not selected.
- * @param iconTextId Text that to be displayed in the navigation UI.
- * @param titleTextId Text that is displayed on the top app bar.
- * @param route The route to use when navigating to this destination.
- * @param baseRoute The highest ancestor of this destination. Defaults to [route], meaning that
- * there is a single destination in that section of the app (no nested destinations).
- */
-/*
-enum class TopLevelDestination(
-    val selectedIcon: ImageVector,
-    val unselectedIcon: ImageVector,
-    @StringRes val iconTextId: Int,
-    @StringRes val titleTextId: Int,
-    val route: KClass<*>,
-    val key: NiaNavKey,
-) {
-    FOR_YOU(
-        selectedIcon = NiaIcons.Upcoming,
-        unselectedIcon = NiaIcons.UpcomingBorder,
-        iconTextId = forYouR.string.feature_foryou_api_title,
-        titleTextId = R.string.app_name,
-        route = ForYouRoute::class,
-        key = ForYouRoute,
-    ),
-    BOOKMARKS(
-        selectedIcon = NiaIcons.Bookmarks,
-        unselectedIcon = NiaIcons.BookmarksBorder,
-        iconTextId = bookmarksR.string.feature_bookmarks_api_title,
-        titleTextId = bookmarksR.string.feature_bookmarks_api_title,
-        route = BookmarksRoute::class,
-        key = BookmarksRoute,
-    ),
-    INTERESTS(
-        selectedIcon = NiaIcons.Grid3x3,
-        unselectedIcon = NiaIcons.Grid3x3,
-        iconTextId = searchR.string.feature_search_api_interests,
-        titleTextId = searchR.string.feature_search_api_interests,
-        route = InterestsRoute::class,
-        key = InterestsRoute(null),
-    ),
-}
-
-internal val TopLevelDestinations = TopLevelDestination.entries.associateBy { dest -> dest.key }
-*/
-
-val FOR_YOU = NavBarItem(
-    selectedIcon = NiaIcons.Upcoming,
-    unselectedIcon = NiaIcons.UpcomingBorder,
-    iconTextId = forYouR.string.feature_foryou_api_title,
-    titleTextId = R.string.app_name,
-    key = ForYouRoute,
-)
-
-val BOOKMARKS = NavBarItem(
-    selectedIcon = NiaIcons.Bookmarks,
-    unselectedIcon = NiaIcons.BookmarksBorder,
-    iconTextId = bookmarksR.string.feature_bookmarks_api_title,
-    titleTextId = bookmarksR.string.feature_bookmarks_api_title,
-    key = BookmarksRoute,
-)
-
-val INTERESTS = NavBarItem(
-    selectedIcon = NiaIcons.Grid3x3,
-    unselectedIcon = NiaIcons.Grid3x3,
-    iconTextId = searchR.string.feature_search_api_interests,
-    titleTextId = searchR.string.feature_search_api_interests,
-    key = InterestsRoute(null)
-)
-
-
-val TOP_LEVEL_ROUTES = mapOf<NavKey, NavBarItem>(
-    ForYouRoute to FOR_YOU,
-    BookmarksRoute to BOOKMARKS,
-    InterestsRoute(null) to INTERESTS,
-)
-
-
-/**
- * Type for the top level navigation items in the application. Contains UI information about the
- * current route that is used in the top app bar and common navigation UI.
- *
- * @param selectedIcon The icon to be displayed in the navigation UI when this destination is
- * selected.
- * @param unselectedIcon The icon to be displayed in the navigation UI when this destination is
- * not selected.
- * @param iconTextId Text that to be displayed in the navigation UI.
- * @param titleTextId Text that is displayed on the top app bar.
- * @param key The navigation key to use when navigating to this destination.
- * there is a single destination in that section of the app (no nested destinations).
- */
-data class NavBarItem(
-    val selectedIcon: ImageVector,
-    val unselectedIcon: ImageVector,
-    @StringRes val iconTextId: Int,
-    @StringRes val titleTextId: Int,
-    val key: NavKey,
-)

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

@@ -1,41 +0,0 @@
-/*
- * Copyright 2025 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.navigation
-
-import androidx.compose.material3.adaptive.ExperimentalMaterial3AdaptiveApi
-import androidx.compose.material3.adaptive.navigation3.rememberListDetailSceneStrategy
-import androidx.compose.runtime.Composable
-import androidx.navigation3.runtime.EntryProviderScope
-import androidx.navigation3.ui.NavDisplay
-import com.google.samples.apps.nowinandroid.core.navigation.NiaNavKey
-import com.google.samples.apps.nowinandroid.core.navigation.NiaNavigator
-import com.google.samples.apps.nowinandroid.core.navigation.toEntries
-
-@OptIn(ExperimentalMaterial3AdaptiveApi::class)
-@Composable
-fun NiaNavDisplay(
-    niaNavigator: NiaNavigator,
-    entryProviderBuilders: Set<EntryProviderScope<NiaNavKey>.() -> Unit>,
-) {
-    val listDetailStrategy = rememberListDetailSceneStrategy<NiaNavKey>()
-    val entries = niaNavigator.niaNavigationState.toEntries(entryProviderBuilders)
-    NavDisplay(
-        entries = entries,
-        sceneStrategy = listDetailStrategy,
-        onBack = { niaNavigator.pop() },
-    )
-}

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

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2025 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.navigation
+
+import androidx.annotation.StringRes
+import androidx.compose.ui.graphics.vector.ImageVector
+
+/**
+ * Type for the top level navigation items in the application. Contains UI information about the
+ * current route that is used in the top app bar and common navigation UI.
+ *
+ * @param selectedIcon The icon to be displayed in the navigation UI when this destination is
+ * selected.
+ * @param unselectedIcon The icon to be displayed in the navigation UI when this destination is
+ * not selected.
+ * @param iconTextId Text that to be displayed in the navigation UI.
+ * @param titleTextId Text that is displayed on the top app bar.
+ */
+data class TopLevelNavItem(
+    val selectedIcon: ImageVector,
+    val unselectedIcon: ImageVector,
+    @StringRes val iconTextId: Int,
+    @StringRes val titleTextId: Int,
+)

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

@@ -0,0 +1,53 @@
+/*
+ * 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.navigation
+
+import com.google.samples.apps.nowinandroid.R
+import com.google.samples.apps.nowinandroid.core.designsystem.icon.NiaIcons
+import com.google.samples.apps.nowinandroid.feature.bookmarks.api.navigation.BookmarksRoute
+import com.google.samples.apps.nowinandroid.feature.foryou.api.navigation.ForYouRoute
+import com.google.samples.apps.nowinandroid.feature.interests.api.navigation.InterestsRoute
+import com.google.samples.apps.nowinandroid.feature.bookmarks.api.R as bookmarksR
+import com.google.samples.apps.nowinandroid.feature.foryou.api.R as forYouR
+import com.google.samples.apps.nowinandroid.feature.search.api.R as searchR
+
+val FOR_YOU = TopLevelNavItem(
+    selectedIcon = NiaIcons.Upcoming,
+    unselectedIcon = NiaIcons.UpcomingBorder,
+    iconTextId = forYouR.string.feature_foryou_api_title,
+    titleTextId = R.string.app_name,
+)
+
+val BOOKMARKS = TopLevelNavItem(
+    selectedIcon = NiaIcons.Bookmarks,
+    unselectedIcon = NiaIcons.BookmarksBorder,
+    iconTextId = bookmarksR.string.feature_bookmarks_api_title,
+    titleTextId = bookmarksR.string.feature_bookmarks_api_title,
+)
+
+val INTERESTS = TopLevelNavItem(
+    selectedIcon = NiaIcons.Grid3x3,
+    unselectedIcon = NiaIcons.Grid3x3,
+    iconTextId = searchR.string.feature_search_api_interests,
+    titleTextId = searchR.string.feature_search_api_interests,
+)
+
+val TOP_LEVEL_ROUTES = mapOf(
+    ForYouRoute to FOR_YOU,
+    BookmarksRoute to BOOKMARKS,
+    InterestsRoute(null) to INTERESTS,
+)

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

@@ -72,8 +72,8 @@ import com.google.samples.apps.nowinandroid.core.designsystem.component.NiaTopAp
 import com.google.samples.apps.nowinandroid.core.designsystem.icon.NiaIcons
 import com.google.samples.apps.nowinandroid.core.designsystem.theme.GradientColors
 import com.google.samples.apps.nowinandroid.core.designsystem.theme.LocalGradientColors
-import com.google.samples.apps.nowinandroid.core.navigation.simple.Navigator
+import com.google.samples.apps.nowinandroid.core.navigation.Navigator
-import com.google.samples.apps.nowinandroid.core.navigation.simple.toEntries
+import com.google.samples.apps.nowinandroid.core.navigation.toEntries
 import com.google.samples.apps.nowinandroid.feature.bookmarks.impl.navigation.LocalSnackbarHostState
 import com.google.samples.apps.nowinandroid.feature.bookmarks.impl.navigation.bookmarksEntry
 import com.google.samples.apps.nowinandroid.feature.foryou.impl.navigation.forYouEntry
@@ -92,7 +92,7 @@ fun NiaApp(
     modifier: Modifier = Modifier,
     windowAdaptiveInfo: WindowAdaptiveInfo = currentWindowAdaptiveInfo(),
 ) {
-    val shouldShowGradientBackground = appState.currentNavBarItem == FOR_YOU
+    val shouldShowGradientBackground = appState.currentTopLevelNavItem == FOR_YOU
     var showSettingsDialog by rememberSaveable { mutableStateOf(false) }
 
     NiaBackground(modifier = modifier) {
@@ -145,7 +145,7 @@ internal fun NiaApp(
     modifier: Modifier = Modifier,
     windowAdaptiveInfo: WindowAdaptiveInfo = currentWindowAdaptiveInfo(),
 ) {
-    val unreadDestinations by appState.topLevelDestinationsWithUnreadResources
+    val unreadRoutes by appState.topLevelRoutesWithUnreadResources
         .collectAsStateWithLifecycle()
 
     if (showSettingsDialog) {
@@ -160,25 +160,25 @@ internal fun NiaApp(
 
     NiaNavigationSuiteScaffold(
         navigationSuiteItems = {
-            TOP_LEVEL_ROUTES.forEach { (navKey, navBarItem) ->
+            TOP_LEVEL_ROUTES.forEach { (route, navItem) ->
-                val hasUnread = unreadDestinations.contains(navBarItem)
+                val hasUnread = unreadRoutes.contains(route)
-                val selected = navKey == appState.navigationState.topLevelRoute
+                val selected = route == appState.navigationState.currentTopLevelKey
                 item(
                     selected = selected,
-                    onClick = { navigator.navigate(navKey) },
+                    onClick = { navigator.navigate(route) },
                     icon = {
                         Icon(
-                            imageVector = navBarItem.unselectedIcon,
+                            imageVector = navItem.unselectedIcon,
                             contentDescription = null,
                         )
                     },
                     selectedIcon = {
                         Icon(
-                            imageVector = navBarItem.selectedIcon,
+                            imageVector = navItem.selectedIcon,
                             contentDescription = null,
                         )
                     },
-                    label = { Text(stringResource(navBarItem.iconTextId)) },
+                    label = { Text(stringResource(navItem.iconTextId)) },
                     modifier = Modifier
                         .testTag("NiaNavItem")
                         .then(if (hasUnread) Modifier.notificationDot() else Modifier),
@@ -217,7 +217,7 @@ internal fun NiaApp(
                     ),
             ) {
                 // Show the top app bar on top level destinations.
-                val destination = appState.currentNavBarItem
+                val destination = appState.currentTopLevelNavItem
                 var shouldShowTopAppBar = false
 
                 if (destination != null) {

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

@@ -20,16 +20,16 @@ import androidx.compose.runtime.Composable
 import androidx.compose.runtime.Stable
 import androidx.compose.runtime.remember
 import androidx.compose.runtime.rememberCoroutineScope
+import androidx.navigation3.runtime.NavKey
 import com.google.samples.apps.nowinandroid.core.data.repository.UserNewsResourceRepository
 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.navigation.simple.NavigationState
+import com.google.samples.apps.nowinandroid.core.navigation.NavigationState
-import com.google.samples.apps.nowinandroid.core.navigation.simple.rememberNavigationState
+import com.google.samples.apps.nowinandroid.core.navigation.rememberNavigationState
+import com.google.samples.apps.nowinandroid.feature.bookmarks.api.navigation.BookmarksRoute
 import com.google.samples.apps.nowinandroid.feature.foryou.api.navigation.ForYouRoute
-import com.google.samples.apps.nowinandroid.navigation.BOOKMARKS
-import com.google.samples.apps.nowinandroid.navigation.FOR_YOU
 import com.google.samples.apps.nowinandroid.navigation.TOP_LEVEL_ROUTES
-import com.google.samples.apps.nowinandroid.navigation.NavBarItem
+import com.google.samples.apps.nowinandroid.navigation.TopLevelNavItem
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.flow.SharingStarted
 import kotlinx.coroutines.flow.StateFlow
@@ -75,8 +75,9 @@ class NiaAppState(
     userNewsResourceRepository: UserNewsResourceRepository,
     timeZoneMonitor: TimeZoneMonitor,
 ) {
-    val currentNavBarItem: NavBarItem?
+    // TODO: I think this should return null if the current route is not a topLevelRoute
-        @Composable get() = TOP_LEVEL_ROUTES[navigationState.topLevelRoute]
+    val currentTopLevelNavItem: TopLevelNavItem?
+        @Composable get() = TOP_LEVEL_ROUTES[navigationState.currentTopLevelKey]
 
     val isOffline = networkMonitor.isOnline
         .map(Boolean::not)
@@ -87,14 +88,14 @@ class NiaAppState(
         )
 
     /**
-     * The top level destinations that have unread news resources.
+     * The top level routes that have unread news resources.
      */
-    val topLevelDestinationsWithUnreadResources: StateFlow<Set<NavBarItem>> =
+    val topLevelRoutesWithUnreadResources: StateFlow<Set<NavKey>> =
         userNewsResourceRepository.observeAllForFollowedTopics()
             .combine(userNewsResourceRepository.observeAllBookmarked()) { forYouNewsResources, bookmarkedNewsResources ->
                 setOfNotNull(
-                    FOR_YOU.takeIf { forYouNewsResources.any { !it.hasBeenViewed } },
+                    ForYouRoute.takeIf { forYouNewsResources.any { !it.hasBeenViewed } },
-                    BOOKMARKS.takeIf { bookmarkedNewsResources.any { !it.hasBeenViewed } },
+                    BookmarksRoute.takeIf { bookmarkedNewsResources.any { !it.hasBeenViewed } },
                 )
             }
             .stateIn(

core/navigation/src/androidTest/kotlin/com/google/samples/apps/nowinandroid/core/navigation/NiaBackStackViewModelTest.kt

@@ -1,253 +0,0 @@
-/*
- * Copyright 2025 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.core.navigation
-
-import androidx.compose.runtime.remember
-import androidx.compose.ui.test.junit4.createComposeRule
-import androidx.lifecycle.SavedStateHandle
-import androidx.lifecycle.createSavedStateHandle
-import androidx.lifecycle.viewmodel.testing.ViewModelScenario
-import androidx.lifecycle.viewmodel.testing.viewModelScenario
-import androidx.test.ext.junit.runners.AndroidJUnit4
-import com.google.common.truth.Truth.assertThat
-import kotlinx.serialization.Serializable
-import kotlinx.serialization.modules.SerializersModule
-import kotlinx.serialization.modules.polymorphic
-import org.junit.Rule
-import org.junit.Test
-import org.junit.runner.RunWith
-
-@RunWith(AndroidJUnit4::class)
-class NiaBackStackViewModelTest {
-
-    @get:Rule val rule = createComposeRule()
-
-    private val serializersModules = SerializersModule {
-        polymorphic(NiaNavKey::class) {
-            subclass(TestStartKey::class, TestStartKey.serializer())
-            subclass(TestTopLevelKeyFirst::class, TestTopLevelKeyFirst.serializer())
-            subclass(TestTopLevelKeySecond::class, TestTopLevelKeySecond.serializer())
-            subclass(TestKeyFirst::class, TestKeyFirst.serializer())
-            subclass(TestKeySecond::class, TestKeySecond.serializer())
-        }
-    }
-
-    private fun createViewModel() = NiaBackStackViewModel(
-        savedStateHandle = SavedStateHandle(),
-        niaNavigationState = NiaNavigationState(TestStartKey),
-        serializersModules = serializersModules,
-    )
-
-    @Test
-    fun testStartKeySaved() {
-        rule.setContent {
-            val viewModel = createViewModel()
-            assertThat(viewModel.backStackMap.size).isEqualTo(1)
-            val entry = viewModel.backStackMap[TestStartKey]
-            assertThat(entry).isNotNull()
-            assertThat(entry).containsExactly(TestStartKey)
-        }
-    }
-
-    @Test
-    fun testNonTopLevelKeySaved() {
-        val viewModel = createViewModel()
-        rule.setContent {
-            val navigator = remember { NiaNavigator(viewModel.niaNavigationState) }
-            navigator.navigate(TestKeyFirst)
-        }
-        assertThat(viewModel.backStackMap.size).isEqualTo(1)
-        val entry = viewModel.backStackMap[TestStartKey]
-        assertThat(entry).isNotNull()
-        assertThat(entry).containsExactly(TestStartKey, TestKeyFirst).inOrder()
-    }
-
-    @Test
-    fun testTopLevelKeySaved() {
-        val viewModel = createViewModel()
-        rule.setContent {
-            val navigator = remember { NiaNavigator(viewModel.niaNavigationState) }
-
-            navigator.navigate(TestKeyFirst)
-            navigator.navigate(TestTopLevelKeyFirst)
-        }
-
-        assertThat(viewModel.backStackMap.size).isEqualTo(2)
-
-        val entry = viewModel.backStackMap[TestStartKey]
-        assertThat(entry).isNotNull()
-        assertThat(entry).containsExactly(TestStartKey, TestKeyFirst).inOrder()
-
-        val entry2 = viewModel.backStackMap[TestTopLevelKeyFirst]
-        assertThat(entry2).isNotNull()
-        assertThat(entry2).containsExactly(TestTopLevelKeyFirst)
-    }
-
-    @Test
-    fun testMultiStacksSaved() {
-        val viewModel = createViewModel()
-        rule.setContent {
-            val navigator = remember { NiaNavigator(viewModel.niaNavigationState) }
-            navigator.navigate(TestKeyFirst)
-            navigator.navigate(TestTopLevelKeyFirst)
-            navigator.navigate(TestKeySecond)
-        }
-
-        assertThat(viewModel.backStackMap.size).isEqualTo(2)
-
-        val entry = viewModel.backStackMap[TestStartKey]
-        assertThat(entry).isNotNull()
-        assertThat(entry).containsExactly(TestStartKey, TestKeyFirst).inOrder()
-
-        val entry2 = viewModel.backStackMap[TestTopLevelKeyFirst]
-        assertThat(entry2).isNotNull()
-        assertThat(entry2).containsExactly(TestTopLevelKeyFirst, TestKeySecond).inOrder()
-    }
-
-    @Test
-    fun testPopSaved() {
-        val viewModel = createViewModel()
-        rule.setContent {
-            val navigator = remember { NiaNavigator(viewModel.niaNavigationState) }
-
-            navigator.navigate(TestKeyFirst)
-
-            assertThat(viewModel.backStackMap.size).isEqualTo(1)
-            val entry = viewModel.backStackMap[TestStartKey]
-            assertThat(entry).isNotNull()
-            assertThat(entry).containsExactly(TestStartKey, TestKeyFirst).inOrder()
-
-            navigator.pop()
-
-            assertThat(viewModel.backStackMap.size).isEqualTo(1)
-            val entry2 = viewModel.backStackMap[TestStartKey]
-            assertThat(entry2).isNotNull()
-            assertThat(entry2).containsExactly(TestStartKey).inOrder()
-        }
-    }
-
-    @Test
-    fun testRestore() {
-        lateinit var scenario: ViewModelScenario<NiaBackStackViewModel>
-        lateinit var navigator: NiaNavigator
-        lateinit var navigatorState: NiaNavigationState
-        rule.setContent {
-            navigatorState = remember { NiaNavigationState(TestStartKey) }
-            navigator = remember { NiaNavigator(navigatorState) }
-            scenario = viewModelScenario {
-                NiaBackStackViewModel(
-                    savedStateHandle = createSavedStateHandle(),
-                    niaNavigationState = navigatorState,
-                    serializersModules = serializersModules,
-                )
-            }
-        }
-
-        rule.runOnIdle {
-            navigator.navigate(TestKeyFirst)
-            assertThat(navigatorState.currentBackStack).containsExactly(
-                TestStartKey,
-                TestKeyFirst,
-            ).inOrder()
-        }
-
-        scenario.recreate()
-
-        rule.runOnIdle {
-            assertThat(navigatorState.currentBackStack).containsExactly(
-                TestStartKey,
-                TestKeyFirst,
-            ).inOrder()
-        }
-
-        scenario.close()
-    }
-
-    @Test
-    fun testRestoreMultiStacks() {
-        lateinit var scenario: ViewModelScenario<NiaBackStackViewModel>
-        lateinit var navigator: NiaNavigator
-        lateinit var navigatorState: NiaNavigationState
-        rule.setContent {
-            navigatorState = remember { NiaNavigationState(TestStartKey) }
-            navigator = remember { NiaNavigator(navigatorState) }
-            scenario = viewModelScenario {
-                NiaBackStackViewModel(
-                    savedStateHandle = createSavedStateHandle(),
-                    niaNavigationState = navigatorState,
-                    serializersModules = serializersModules,
-                )
-            }
-        }
-
-        rule.runOnIdle {
-            navigator.navigate(TestKeyFirst)
-            navigator.navigate(TestTopLevelKeyFirst)
-            navigator.navigate(TestKeySecond)
-
-            assertThat(navigatorState.currentBackStack).containsExactly(
-                TestStartKey,
-                TestKeyFirst,
-                TestTopLevelKeyFirst,
-                TestKeySecond,
-            ).inOrder()
-        }
-
-        scenario.recreate()
-
-        rule.runOnIdle {
-            assertThat(navigatorState.currentBackStack).containsExactly(
-                TestStartKey,
-                TestKeyFirst,
-                TestTopLevelKeyFirst,
-                TestKeySecond,
-            ).inOrder()
-        }
-
-        scenario.close()
-    }
-}
-
-@Serializable
-private object TestStartKey : NiaNavKey {
-    override val isTopLevel: Boolean
-        get() = true
-}
-
-@Serializable
-private object TestTopLevelKeyFirst : NiaNavKey {
-    override val isTopLevel: Boolean
-        get() = true
-}
-
-@Serializable
-private object TestTopLevelKeySecond : NiaNavKey {
-    override val isTopLevel: Boolean
-        get() = true
-}
-
-@Serializable
-private object TestKeyFirst : NiaNavKey {
-    override val isTopLevel: Boolean
-        get() = false
-}
-
-@Serializable
-private object TestKeySecond : NiaNavKey {
-    override val isTopLevel: Boolean
-        get() = false
-}

core/navigation/src/main/kotlin/com/google/samples/apps/nowinandroid/core/navigation/NavigationState.kt

@@ -5,7 +5,7 @@
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
- *     http://www.apache.org/licenses/LICENSE-2.0
+ *     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,
@@ -14,15 +14,13 @@
  * limitations under the License.
  */
 
-package com.google.samples.apps.nowinandroid.core.navigation.simple
+package com.google.samples.apps.nowinandroid.core.navigation
 
+import androidx.annotation.VisibleForTesting
 import androidx.compose.runtime.Composable
-import androidx.compose.runtime.MutableState
+import androidx.compose.runtime.derivedStateOf
 import androidx.compose.runtime.getValue
-import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
-import androidx.compose.runtime.saveable.rememberSerializable
-import androidx.compose.runtime.setValue
 import androidx.compose.runtime.snapshots.SnapshotStateList
 import androidx.compose.runtime.toMutableStateList
 import androidx.navigation3.runtime.NavBackStack
@@ -31,32 +29,24 @@ import androidx.navigation3.runtime.NavKey
 import androidx.navigation3.runtime.rememberDecoratedNavEntries
 import androidx.navigation3.runtime.rememberNavBackStack
 import androidx.navigation3.runtime.rememberSaveableStateHolderNavEntryDecorator
-import androidx.navigation3.runtime.serialization.NavKeySerializer
-import androidx.savedstate.compose.serialization.serializers.MutableStateSerializer
 
 /**
  * Create a navigation state that persists config changes and process death.
  */
 @Composable
 fun rememberNavigationState(
-    startRoute: NavKey,
+    startKey: NavKey,
-    topLevelRoutes: Set<NavKey>
+    topLevelKeys: Set<NavKey>
 ): NavigationState {
 
-    val topLevelRoute = rememberSerializable(
+    val topLevelStack = rememberNavBackStack(startKey)
-        startRoute, topLevelRoutes,
+    val subStacks = topLevelKeys.associateWith { key -> rememberNavBackStack(key) }
-        serializer = MutableStateSerializer(NavKeySerializer())
-    ) {
-        mutableStateOf(startRoute)
-    }
-
-    val backStacks = topLevelRoutes.associateWith { key -> rememberNavBackStack(key) }
 
-    return remember(startRoute, topLevelRoutes) {
+    return remember(startKey, topLevelKeys) {
         NavigationState(
-            startRoute = startRoute,
+            startKey = startKey,
-            topLevelRoute = topLevelRoute,
+            topLevelStack = topLevelStack,
-            backStacks = backStacks
+            subStacks = subStacks
         )
     }
 }
@@ -64,23 +54,37 @@ fun rememberNavigationState(
 /**
  * State holder for navigation state.
  *
- * @param startRoute - the start route. The user will exit the app through this route.
+ * @param startKey - the starting navigation key. The user will exit the app through this key.
- * @param topLevelRoute - the current top level route
+ * @param currentTopLevelKey - the current top level key
- * @param backStacks - the back stacks for each top level route
+ * @param subStacks - the back stacks for each top level key
  */
 class NavigationState(
-    val startRoute: NavKey,
+    val startKey: NavKey,
-    topLevelRoute: MutableState<NavKey>,
+    val topLevelStack: NavBackStack<NavKey>,
-    val backStacks: Map<NavKey, NavBackStack<NavKey>>
+    val subStacks: Map<NavKey, NavBackStack<NavKey>>
 ) {
-    var topLevelRoute: NavKey by topLevelRoute
+    val currentTopLevelKey: NavKey by derivedStateOf { topLevelStack.last() }
-    val stacksInUse: List<NavKey>
+
-        get() = if (topLevelRoute == startRoute) {
+    val topLevelKeys
+        get() = subStacks.keys
+
+    @get:VisibleForTesting
+    val currentSubStack : NavBackStack<NavKey>
+        get() = subStacks[currentTopLevelKey]
+            ?: error("Sub stack for $currentTopLevelKey does not exist")
+
+    @get:VisibleForTesting
+    val currentKey
+        get() = currentSubStack?.last()
+
+    // TODO: Fix this
+    /*val stacksInUse: List<NavKey>
+        get() = topLevel
             listOf(startRoute)
         } else {
             listOf(startRoute, topLevelRoute)
         }
-
+*/
 }
 
 /**
@@ -91,7 +95,7 @@ fun NavigationState.toEntries(
     entryProvider: (NavKey) -> NavEntry<NavKey>
 ): SnapshotStateList<NavEntry<NavKey>> {
 
-    val decoratedEntries = backStacks.mapValues { (_, stack) ->
+    val decoratedEntries = subStacks.mapValues { (_, stack) ->
         val decorators = listOf(
             rememberSaveableStateHolderNavEntryDecorator<NavKey>(),
         )
@@ -102,7 +106,7 @@ fun NavigationState.toEntries(
         )
     }
 
-    return stacksInUse
+    return topLevelStack
         .flatMap { decoratedEntries[it] ?: emptyList() }
         .toMutableStateList()
 }

core/navigation/src/main/kotlin/com/google/samples/apps/nowinandroid/core/navigation/Navigator.kt

@@ -0,0 +1,91 @@
+/*
+ * Copyright 2025 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.core.navigation
+
+import androidx.navigation3.runtime.NavKey
+
+/**
+ * Handles navigation events (forward and back) by updating the navigation state.
+ *
+ * @param state - The navigation state that will be updated in response to navigation events.
+ */
+class Navigator(val state: NavigationState) {
+
+    /**
+     * Navigate to a navigation key
+     *
+     * @param key - the navigation key to navigate to.
+     */
+    fun navigate(key: NavKey) {
+        when (key) {
+            state.currentTopLevelKey -> goUp()
+            in state.topLevelKeys -> goToTopLevel(key)
+            else -> goToKey(key)
+        }
+    }
+
+    /**
+     * Go back to the previous navigation key.
+     */
+    fun goBack() {
+        when (state.currentKey){
+            state.startKey -> error("You cannot go back from the start route")
+            state.currentTopLevelKey -> {
+                // We're at the base of the current sub stack, go back to the previous top level
+                // stack.
+                state.topLevelStack.removeLastOrNull()
+            }
+            else -> state.currentSubStack.removeLastOrNull()
+        }
+    }
+
+    /**
+     * Go to a non top level key.
+     */
+    private fun goToKey(key: NavKey) {
+        state.currentSubStack.apply {
+            // Remove it if it's already in the stack so it's added at the end.
+            remove(key)
+            add(key)
+        }
+    }
+
+    /**
+     * Go to a top level stack.
+     */
+    private fun goToTopLevel(key: NavKey) {
+        state.topLevelStack.apply {
+            if (key == state.startKey) {
+                // This is the start key. Clear the stack so it's added as the only key.
+                clear()
+            } else {
+                // Remove it if it's already in the stack so it's added at the end.
+                remove(key)
+            }
+            add(key)
+        }
+    }
+
+    /**
+     * Go up in the current sub stack by clearing all but the root key.
+     */
+    private fun goUp() {
+        state.currentSubStack.run {
+            if (size > 1) subList(1, size).clear()
+        }
+    }
+}

core/navigation/src/main/kotlin/com/google/samples/apps/nowinandroid/core/navigation/NiaBackStackViewModel.kt

@@ -1,90 +0,0 @@
-/*
- * Copyright 2025 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.core.navigation
-
-import androidx.annotation.VisibleForTesting
-import androidx.compose.runtime.snapshotFlow
-import androidx.compose.runtime.snapshots.SnapshotStateList
-import androidx.lifecycle.SavedStateHandle
-import androidx.lifecycle.ViewModel
-import androidx.lifecycle.serialization.saved
-import androidx.lifecycle.viewModelScope
-import androidx.savedstate.serialization.SavedStateConfiguration
-import dagger.hilt.android.lifecycle.HiltViewModel
-import kotlinx.coroutines.flow.collect
-import kotlinx.coroutines.launch
-import kotlinx.serialization.builtins.ListSerializer
-import kotlinx.serialization.builtins.MapSerializer
-import kotlinx.serialization.modules.SerializersModule
-import kotlinx.serialization.serializer
-import javax.inject.Inject
-
-/**
- * TODO: I'm not sure why this needs to be a ViewModel - why can't it be a plain state holder that
- *  is scoped to `NiaAppState`?
- *  https://github.com/android/nav3-recipes/blob/main/app/src/main/java/com/example/nav3recipes/multiplestacks/NavigationState.kt#L71
- *
- */
-/*
-@HiltViewModel
-class NiaBackStackViewModel @Inject constructor(
-    savedStateHandle: SavedStateHandle,
-    val niaNavigationState: NiaNavigationState,
-    serializersModules: SerializersModule,
-) : ViewModel() {
-
-    private val config = SavedStateConfiguration { serializersModule = serializersModules }
-
-    @VisibleForTesting
-    internal var backStackMap by savedStateHandle.saved(
-        serializer = MapSerializer(
-            serializer<NiaNavKey>(),
-            serializer<List<NiaNavKey>>(),
-        ),
-        configuration = config,
-    ) {
-        linkedMapOf()
-    }
-
-    @VisibleForTesting
-    internal var activeTopLeveLKeys by savedStateHandle.saved(
-        serializer = ListSerializer(serializer<NiaNavKey>()),
-        configuration = config,
-    ) {
-        listOf()
-    }
-
-    init {
-        if (backStackMap.isNotEmpty()) {
-            // Restore backstack from saved state handle if not empty
-            @Suppress("UNCHECKED_CAST")
-            niaNavigationState.restore(
-                activeTopLeveLKeys,
-                backStackMap as LinkedHashMap<NiaNavKey, SnapshotStateList<NiaNavKey>>,
-            )
-        }
-
-        // Start observing changes to the backStack and save backStack whenever it updates
-        viewModelScope.launch {
-            snapshotFlow {
-                activeTopLeveLKeys = niaNavigationState.activeTopLeveLKeys.toList()
-                backStackMap = niaNavigationState.backStacks
-            }.collect()
-        }
-    }
-}
-*/

core/navigation/src/main/kotlin/com/google/samples/apps/nowinandroid/core/navigation/NiaNavigator.kt

@@ -1,173 +0,0 @@
-/*
- * Copyright 2025 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.core.navigation
-
-import androidx.compose.runtime.Composable
-import androidx.compose.runtime.getValue
-import androidx.compose.runtime.key
-import androidx.compose.runtime.mutableStateListOf
-import androidx.compose.runtime.mutableStateOf
-import androidx.compose.runtime.setValue
-import androidx.compose.runtime.snapshots.SnapshotStateList
-import androidx.compose.runtime.toMutableStateList
-import androidx.lifecycle.viewmodel.navigation3.rememberViewModelStoreNavEntryDecorator
-import androidx.navigation3.runtime.EntryProviderScope
-import androidx.navigation3.runtime.NavEntry
-import androidx.navigation3.runtime.entryProvider
-import androidx.navigation3.runtime.rememberDecoratedNavEntries
-import androidx.navigation3.runtime.rememberSaveableStateHolderNavEntryDecorator
-import org.jetbrains.annotations.VisibleForTesting
-import javax.inject.Inject
-import kotlin.collections.plus
-
-// TODO: Consider changing this to `NiaNavigationState`
-class NiaNavigationState(
-    internal val startKey: NiaNavKey,
-) {
-    internal var backStacks: MutableMap<NiaNavKey, SnapshotStateList<NiaNavKey>> =
-        linkedMapOf(
-            startKey to mutableStateListOf(startKey),
-        )
-
-    val activeTopLeveLKeys: SnapshotStateList<NiaNavKey> = mutableStateListOf(startKey)
-
-    var currentTopLevelKey: NiaNavKey by mutableStateOf(activeTopLeveLKeys.last())
-        private set
-
-    @get:VisibleForTesting
-    val currentBackStack: List<NiaNavKey>
-        get() = activeTopLeveLKeys.fold(mutableListOf()) { list, topLevelKey ->
-            list.apply {
-                addAll(backStacks[topLevelKey] ?: error("No back stack found for $topLevelKey"))
-            }
-        }
-
-    @get:VisibleForTesting
-    val currentKey: NiaNavKey
-        get() = backStacks[currentTopLevelKey]!!.last()
-
-    internal fun updateActiveTopLevelKeys(activeKeys: List<NiaNavKey>) {
-        check(activeKeys.isNotEmpty()) { "List of active top-level keys should not be empty" }
-        activeTopLeveLKeys.clear()
-        activeTopLeveLKeys.addAll(activeKeys)
-        currentTopLevelKey = activeTopLeveLKeys.last()
-    }
-
-    internal fun restore(activeKeys: List<NiaNavKey>, map: LinkedHashMap<NiaNavKey, SnapshotStateList<NiaNavKey>>?) {
-        map ?: return
-        backStacks.clear()
-        map.forEach { entry ->
-            backStacks[entry.key] = entry.value.toMutableStateList()
-        }
-        updateActiveTopLevelKeys(activeKeys)
-    }
-}
-
-/**
- * TODO: Document this
- */
-class NiaNavigator @Inject constructor(
-    val niaNavigationState: NiaNavigationState,
-) {
-    // TODO: I wonder if it'd be simpler to have separate methods
-    //  for navigating to a graph and navigating to a key. If the key is on a separate graph then
-    //  navigate to that graph first.
-    fun navigate(key: NiaNavKey) {
-        val currentActiveSubStacks = linkedSetOf<NiaNavKey>()
-        niaNavigationState.apply {
-            currentActiveSubStacks.addAll(activeTopLeveLKeys)
-            when {
-                // top level singleTop -> clear substack
-                key == currentTopLevelKey -> {
-                    backStacks[key] = mutableStateListOf(key)
-                    // no change to currentActiveTabs
-                }
-                // top level non-singleTop
-                key.isTopLevel -> {
-                    // if navigating back to start destination, then only show the starting substack
-                    if (key == startKey) {
-                        currentActiveSubStacks.clear()
-                        currentActiveSubStacks.add(key)
-                    } else {
-                        // else either restore an existing substack or initiate new one
-                        backStacks[key] = backStacks.remove(key) ?: mutableStateListOf(key)
-                        // move this top level key to the top of active substacks
-                        currentActiveSubStacks.remove(key)
-                        currentActiveSubStacks.add(key)
-                    }
-                }
-                // not top level - add to current substack
-                else -> {
-                    val currentStack = backStacks[currentTopLevelKey]!!
-                    // single top
-                    if (currentStack.lastOrNull() == key) {
-                        currentStack.removeLastOrNull()
-                    }
-                    currentStack.add(key)
-                    // no change to currentActiveTabs
-                }
-            }
-            updateActiveTopLevelKeys(currentActiveSubStacks.toList())
-        }
-    }
-
-    fun pop() {
-        niaNavigationState.apply {
-            val currentSubstack = backStacks[currentTopLevelKey]!!
-            if (currentSubstack.size == 1) {
-                // if current sub-stack only has one key, remove the sub-stack from the map
-                currentSubstack.removeLastOrNull()
-                backStacks.remove(currentTopLevelKey)
-                updateActiveTopLevelKeys(activeTopLeveLKeys.dropLast(1))
-            } else {
-                currentSubstack.removeLastOrNull()
-            }
-        }
-    }
-}
-
-// TODO: I wonder if removing this would remove the need for the serializers modules
-interface NiaNavKey {
-    val isTopLevel: Boolean
-}
-
-/**
- * Convert the navigation state to `NavEntry`s that can be displayed by a `NavDisplay`
- */
-@Composable
-fun NiaNavigationState.toEntries(
-    // TODO: Might be better to pass this in fully constructed
-    entryProviderBuilders: Set<EntryProviderScope<NiaNavKey>.() -> Unit>,
-): List<NavEntry<NiaNavKey>> =
-    activeTopLeveLKeys.fold(emptyList()) { entries, topLevelKey ->
-        val decorated = key(topLevelKey) {
-            val decorators = listOf(
-                rememberSaveableStateHolderNavEntryDecorator(),
-                rememberViewModelStoreNavEntryDecorator<NiaNavKey>(),
-            )
-            rememberDecoratedNavEntries(
-                backStack = backStacks[topLevelKey]!!,
-                entryDecorators = decorators,
-                entryProvider = entryProvider {
-                    entryProviderBuilders.forEach { builder ->
-                        builder()
-                    }
-                },
-            )
-        }
-        entries + decorated
-    }

core/navigation/src/main/kotlin/com/google/samples/apps/nowinandroid/core/navigation/simple/Navigator.kt

@@ -1,46 +0,0 @@
-/*
- * Copyright 2025 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
- *
- *     http://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.core.navigation.simple
-
-import androidx.navigation3.runtime.NavKey
-
-/**
- * Handles navigation events (forward and back) by updating the navigation state.
- */
-class Navigator(val state: NavigationState){
-    fun navigate(route: NavKey){
-        if (route in state.backStacks.keys){
-            // This is a top level route, just switch to it
-            state.topLevelRoute = route
-        } else {
-            state.backStacks[state.topLevelRoute]?.add(route)
-        }
-    }
-
-    fun goBack(){
-        val currentStack = state.backStacks[state.topLevelRoute] ?:
-        error("Stack for ${state.topLevelRoute} not found")
-        val currentRoute = currentStack.last()
-
-        // If we're at the base of the current route, go back to the start route stack.
-        if (currentRoute == state.topLevelRoute){
-            state.topLevelRoute = state.startRoute
-        } else {
-            currentStack.removeLastOrNull()
-        }
-    }
-}

core/navigation/src/test/kotlin/com/google/samples/apps/nowinandroid/core/navigation/NavigatorTest.kt

@@ -0,0 +1,260 @@
+/*
+ * Copyright 2025 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.core.navigation
+
+import androidx.navigation3.runtime.NavBackStack
+import androidx.navigation3.runtime.NavKey
+import com.google.common.truth.Truth.assertThat
+import org.junit.Before
+import org.junit.Test
+import kotlin.test.assertFailsWith
+
+private object TestFirstTopLevelKey : NavKey
+private object TestSecondTopLevelKey : NavKey
+private object TestThirdTopLevelKey : NavKey
+private object TestKeyFirst : NavKey
+private object TestKeySecond : NavKey
+
+class NavigatorTest {
+
+    private lateinit var navigationState: NavigationState
+    private lateinit var navigator: Navigator
+
+    @Before
+    fun setup() {
+
+        val startKey = TestFirstTopLevelKey
+        val topLevelStack = NavBackStack<NavKey>(startKey)
+        val topLevelKeys = listOf(
+            startKey,
+            TestSecondTopLevelKey,
+            TestThirdTopLevelKey
+        )
+        val subStacks = topLevelKeys.associateWith { key -> NavBackStack(key) }
+
+        navigationState = NavigationState(
+            startKey = startKey,
+            topLevelStack = topLevelStack,
+            subStacks = subStacks
+        )
+        navigator = Navigator(navigationState)
+    }
+
+    @Test
+    fun testStartKey() {
+        assertThat(navigationState.startKey).isEqualTo(TestFirstTopLevelKey)
+        assertThat(navigationState.currentTopLevelKey).isEqualTo(TestFirstTopLevelKey)
+    }
+
+    @Test
+    fun testNavigate() {
+        navigator.navigate(TestKeyFirst)
+
+        assertThat(navigationState.currentTopLevelKey).isEqualTo(TestFirstTopLevelKey)
+        assertThat(navigationState.subStacks[TestFirstTopLevelKey]?.last()).isEqualTo(TestKeyFirst)
+        
+    }
+
+    @Test
+    fun testNavigateTopLevel() {
+        navigator.navigate(TestSecondTopLevelKey)
+        assertThat(navigationState.currentTopLevelKey).isEqualTo(TestSecondTopLevelKey)
+    }
+
+    @Test
+    fun testNavigateSingleTop() {
+        navigator.navigate(TestKeyFirst)
+
+        assertThat(navigationState.currentSubStack).containsExactly(
+            TestFirstTopLevelKey,
+            TestKeyFirst,
+        ).inOrder()
+
+        navigator.navigate(TestKeyFirst)
+
+        assertThat(navigationState.currentSubStack).containsExactly(
+            TestFirstTopLevelKey,
+            TestKeyFirst,
+        ).inOrder()
+    }
+
+    @Test
+    fun testNavigateTopLevelSingleTop() {
+        navigator.navigate(TestSecondTopLevelKey)
+        navigator.navigate(TestKeyFirst)
+
+        assertThat(navigationState.currentSubStack).containsExactly(
+            TestSecondTopLevelKey,
+            TestKeyFirst,
+        ).inOrder()
+
+        navigator.navigate(TestSecondTopLevelKey)
+
+        assertThat(navigationState.currentSubStack).containsExactly(
+            TestSecondTopLevelKey,
+        ).inOrder()
+    }
+
+    @Test
+    fun testSubStack() {
+        navigator.navigate(TestKeyFirst)
+
+        assertThat(navigationState.currentKey).isEqualTo(TestKeyFirst)
+        assertThat(navigationState.currentTopLevelKey).isEqualTo(TestFirstTopLevelKey)
+
+        navigator.navigate(TestKeySecond)
+
+        assertThat(navigationState.currentKey).isEqualTo(TestKeySecond)
+        assertThat(navigationState.currentTopLevelKey).isEqualTo(TestFirstTopLevelKey)
+    }
+
+    @Test
+    fun testMultiStack() {
+        // add to start stack
+        navigator.navigate(TestKeyFirst)
+
+        assertThat(navigationState.currentKey).isEqualTo(TestKeyFirst)
+        assertThat(navigationState.currentTopLevelKey).isEqualTo(TestFirstTopLevelKey)
+
+        // navigate to new top level
+        navigator.navigate(TestSecondTopLevelKey)
+
+        assertThat(navigationState.currentKey).isEqualTo(TestSecondTopLevelKey)
+        assertThat(navigationState.currentTopLevelKey).isEqualTo(TestSecondTopLevelKey)
+
+        // add to new stack
+        navigator.navigate(TestKeySecond)
+
+        assertThat(navigationState.currentKey).isEqualTo(TestKeySecond)
+        assertThat(navigationState.currentTopLevelKey).isEqualTo(TestSecondTopLevelKey)
+
+        // go back to start stack
+        navigator.navigate(TestFirstTopLevelKey)
+
+        assertThat(navigationState.currentKey).isEqualTo(TestKeyFirst)
+        assertThat(navigationState.currentTopLevelKey).isEqualTo(TestFirstTopLevelKey)
+    }
+    
+    @Test
+    fun testPopOneNonTopLevel() {
+        navigator.navigate(TestKeyFirst)
+        navigator.navigate(TestKeySecond)
+
+        assertThat(navigationState.currentSubStack).containsExactly(
+            TestFirstTopLevelKey,
+            TestKeyFirst,
+            TestKeySecond,
+        ).inOrder()
+
+        navigator.goBack()
+
+        assertThat(navigationState.currentSubStack).containsExactly(
+            TestFirstTopLevelKey,
+            TestKeyFirst,
+        ).inOrder()
+
+        assertThat(navigationState.currentKey).isEqualTo(TestKeyFirst)
+        assertThat(navigationState.currentTopLevelKey).isEqualTo(TestFirstTopLevelKey)
+    }
+
+    @Test
+    fun testPopOneTopLevel() {
+        navigator.navigate(TestKeyFirst)
+        navigator.navigate(TestSecondTopLevelKey)
+
+        assertThat(navigationState.currentSubStack).containsExactly(
+            TestSecondTopLevelKey,
+        ).inOrder()
+
+        assertThat(navigationState.currentKey).isEqualTo(TestSecondTopLevelKey)
+        assertThat(navigationState.currentTopLevelKey).isEqualTo(TestSecondTopLevelKey)
+
+        // remove TopLevel
+        navigator.goBack()
+
+        assertThat(navigationState.currentSubStack).containsExactly(
+            TestFirstTopLevelKey,
+            TestKeyFirst,
+        ).inOrder()
+
+        assertThat(navigationState.currentKey).isEqualTo(TestKeyFirst)
+        assertThat(navigationState.currentTopLevelKey).isEqualTo(TestFirstTopLevelKey)
+    }
+
+    @Test
+    fun popMultipleNonTopLevel() {
+        navigator.navigate(TestKeyFirst)
+        navigator.navigate(TestKeySecond)
+
+        assertThat(navigationState.currentSubStack).containsExactly(
+            TestFirstTopLevelKey,
+            TestKeyFirst,
+            TestKeySecond,
+        ).inOrder()
+
+        navigator.goBack()
+        navigator.goBack()
+
+        assertThat(navigationState.currentSubStack).containsExactly(
+            TestFirstTopLevelKey,
+        ).inOrder()
+
+        assertThat(navigationState.currentKey).isEqualTo(TestFirstTopLevelKey)
+        assertThat(navigationState.currentTopLevelKey).isEqualTo(TestFirstTopLevelKey)
+    }
+
+    @Test
+    fun popMultipleTopLevel() {
+        // second sub-stack
+        navigator.navigate(TestSecondTopLevelKey)
+        navigator.navigate(TestKeyFirst)
+
+        assertThat(navigationState.currentSubStack).containsExactly(
+            TestSecondTopLevelKey,
+            TestKeyFirst,
+        ).inOrder()
+
+        // third sub-stack
+        navigator.navigate(TestThirdTopLevelKey)
+        navigator.navigate(TestKeySecond)
+
+        assertThat(navigationState.currentSubStack).containsExactly(
+            TestThirdTopLevelKey,
+            TestKeySecond,
+        ).inOrder()
+
+        repeat(4) {
+            navigator.goBack()
+        }
+
+        assertThat(navigationState.currentSubStack).containsExactly(
+            TestFirstTopLevelKey,
+        ).inOrder()
+
+        assertThat(navigationState.currentKey).isEqualTo(TestFirstTopLevelKey)
+        assertThat(navigationState.currentTopLevelKey).isEqualTo(TestFirstTopLevelKey)
+    }
+
+    @Test
+    fun throwOnEmptyBackStack() {
+        assertFailsWith<IllegalStateException> {
+            navigator.goBack()
+        }
+    }
+}
+
+

core/navigation/src/test/kotlin/com/google/samples/apps/nowinandroid/core/navigation/NiaNavigatorStateTest.kt

@@ -1,287 +0,0 @@
-/*
- * Copyright 2025 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.core.navigation
-
-import androidx.compose.runtime.mutableStateListOf
-import com.google.common.truth.Truth.assertThat
-import org.junit.Before
-import org.junit.Test
-import kotlin.test.assertFailsWith
-
-class NiaNavigatorStateTest {
-
-    private lateinit var niaNavigationState: NiaNavigationState
-    private lateinit var niaNavigator: NiaNavigator
-
-    @Before
-    fun setup() {
-        niaNavigationState = NiaNavigationState(TestStartKey)
-        niaNavigator = NiaNavigator(niaNavigationState)
-    }
-
-    @Test
-    fun testStartKey() {
-        assertThat(niaNavigationState.currentKey).isEqualTo(TestStartKey)
-        assertThat(niaNavigationState.currentTopLevelKey).isEqualTo(TestStartKey)
-    }
-
-    @Test
-    fun testNavigate() {
-        niaNavigator.navigate(TestKeyFirst)
-
-        assertThat(niaNavigationState.currentKey).isEqualTo(TestKeyFirst)
-        assertThat(niaNavigationState.currentTopLevelKey).isEqualTo(TestStartKey)
-    }
-
-    @Test
-    fun testNavigateTopLevel() {
-        niaNavigator.navigate(TestTopLevelKey)
-
-        assertThat(niaNavigationState.currentKey).isEqualTo(TestTopLevelKey)
-        assertThat(niaNavigationState.currentTopLevelKey).isEqualTo(TestTopLevelKey)
-    }
-
-    @Test
-    fun testNavigateSingleTop() {
-        niaNavigator.navigate(TestKeyFirst)
-
-        assertThat(niaNavigationState.currentBackStack).containsExactly(
-            TestStartKey,
-            TestKeyFirst,
-        ).inOrder()
-
-        niaNavigator.navigate(TestKeyFirst)
-
-        assertThat(niaNavigationState.currentBackStack).containsExactly(
-            TestStartKey,
-            TestKeyFirst,
-        ).inOrder()
-    }
-
-    @Test
-    fun testNavigateTopLevelSingleTop() {
-        niaNavigator.navigate(TestTopLevelKey)
-        niaNavigator.navigate(TestKeyFirst)
-
-        assertThat(niaNavigationState.currentBackStack).containsExactly(
-            TestStartKey,
-            TestTopLevelKey,
-            TestKeyFirst,
-        ).inOrder()
-
-        niaNavigator.navigate(TestTopLevelKey)
-
-        assertThat(niaNavigationState.currentBackStack).containsExactly(
-            TestStartKey,
-            TestTopLevelKey,
-        ).inOrder()
-    }
-
-    @Test
-    fun testSubStack() {
-        niaNavigator.navigate(TestKeyFirst)
-
-        assertThat(niaNavigationState.currentKey).isEqualTo(TestKeyFirst)
-        assertThat(niaNavigationState.currentTopLevelKey).isEqualTo(TestStartKey)
-
-        niaNavigator.navigate(TestKeySecond)
-
-        assertThat(niaNavigationState.currentKey).isEqualTo(TestKeySecond)
-        assertThat(niaNavigationState.currentTopLevelKey).isEqualTo(TestStartKey)
-    }
-
-    @Test
-    fun testMultiStack() {
-        // add to start stack
-        niaNavigator.navigate(TestKeyFirst)
-
-        assertThat(niaNavigationState.currentKey).isEqualTo(TestKeyFirst)
-        assertThat(niaNavigationState.currentTopLevelKey).isEqualTo(TestStartKey)
-
-        // navigate to new top level
-        niaNavigator.navigate(TestTopLevelKey)
-
-        assertThat(niaNavigationState.currentKey).isEqualTo(TestTopLevelKey)
-        assertThat(niaNavigationState.currentTopLevelKey).isEqualTo(TestTopLevelKey)
-
-        // add to new stack
-        niaNavigator.navigate(TestKeySecond)
-
-        assertThat(niaNavigationState.currentKey).isEqualTo(TestKeySecond)
-        assertThat(niaNavigationState.currentTopLevelKey).isEqualTo(TestTopLevelKey)
-
-        // go back to start stack
-        niaNavigator.navigate(TestStartKey)
-
-        assertThat(niaNavigationState.currentKey).isEqualTo(TestKeyFirst)
-        assertThat(niaNavigationState.currentTopLevelKey).isEqualTo(TestStartKey)
-    }
-
-    @Test
-    fun testRestore() {
-        assertThat(niaNavigationState.currentBackStack).containsExactly(TestStartKey)
-
-        niaNavigationState.restore(
-            listOf(TestStartKey, TestTopLevelKey),
-            linkedMapOf(
-                TestStartKey to mutableStateListOf(TestStartKey, TestKeyFirst),
-                TestTopLevelKey to mutableStateListOf(TestTopLevelKey, TestKeySecond),
-            ),
-        )
-
-        assertThat(niaNavigationState.currentBackStack).containsExactly(
-            TestStartKey,
-            TestKeyFirst,
-            TestTopLevelKey,
-            TestKeySecond,
-        ).inOrder()
-
-        assertThat(niaNavigationState.currentKey).isEqualTo(TestKeySecond)
-        assertThat(niaNavigationState.currentTopLevelKey).isEqualTo(TestTopLevelKey)
-    }
-
-    @Test
-    fun testPopOneNonTopLevel() {
-        niaNavigator.navigate(TestKeyFirst)
-        niaNavigator.navigate(TestKeySecond)
-
-        assertThat(niaNavigationState.currentBackStack).containsExactly(
-            TestStartKey,
-            TestKeyFirst,
-            TestKeySecond,
-        ).inOrder()
-
-        niaNavigator.pop()
-
-        assertThat(niaNavigationState.currentBackStack).containsExactly(
-            TestStartKey,
-            TestKeyFirst,
-        ).inOrder()
-
-        assertThat(niaNavigationState.currentKey).isEqualTo(TestKeyFirst)
-        assertThat(niaNavigationState.currentTopLevelKey).isEqualTo(TestStartKey)
-    }
-
-    @Test
-    fun testPopOneTopLevel() {
-        niaNavigator.navigate(TestKeyFirst)
-        niaNavigator.navigate(TestTopLevelKey)
-
-        assertThat(niaNavigationState.currentBackStack).containsExactly(
-            TestStartKey,
-            TestKeyFirst,
-            TestTopLevelKey,
-        ).inOrder()
-
-        assertThat(niaNavigationState.currentKey).isEqualTo(TestTopLevelKey)
-        assertThat(niaNavigationState.currentTopLevelKey).isEqualTo(TestTopLevelKey)
-
-        // remove TopLevel
-        niaNavigator.pop()
-
-        assertThat(niaNavigationState.currentBackStack).containsExactly(
-            TestStartKey,
-            TestKeyFirst,
-        ).inOrder()
-
-        assertThat(niaNavigationState.currentKey).isEqualTo(TestKeyFirst)
-        assertThat(niaNavigationState.currentTopLevelKey).isEqualTo(TestStartKey)
-    }
-
-    @Test
-    fun popMultipleNonTopLevel() {
-        niaNavigator.navigate(TestKeyFirst)
-        niaNavigator.navigate(TestKeySecond)
-
-        assertThat(niaNavigationState.currentBackStack).containsExactly(
-            TestStartKey,
-            TestKeyFirst,
-            TestKeySecond,
-        ).inOrder()
-
-        niaNavigator.pop()
-        niaNavigator.pop()
-
-        assertThat(niaNavigationState.currentBackStack).containsExactly(
-            TestStartKey,
-        ).inOrder()
-
-        assertThat(niaNavigationState.currentKey).isEqualTo(TestStartKey)
-        assertThat(niaNavigationState.currentTopLevelKey).isEqualTo(TestStartKey)
-    }
-
-    @Test
-    fun popMultipleTopLevel() {
-        val testTopLevelKeyTwo = object : NiaNavKey {
-            override val isTopLevel: Boolean
-                get() = true
-        }
-
-        // second sub-stack
-        niaNavigator.navigate(TestTopLevelKey)
-        niaNavigator.navigate(TestKeyFirst)
-        // third sub-stack
-        niaNavigator.navigate(testTopLevelKeyTwo)
-        niaNavigator.navigate(TestKeySecond)
-
-        assertThat(niaNavigationState.currentBackStack).containsExactly(
-            TestStartKey,
-            TestTopLevelKey,
-            TestKeyFirst,
-            testTopLevelKeyTwo,
-            TestKeySecond,
-        ).inOrder()
-
-        repeat(4) {
-            niaNavigator.pop()
-        }
-
-        assertThat(niaNavigationState.currentBackStack).containsExactly(
-            TestStartKey,
-        ).inOrder()
-
-        assertThat(niaNavigationState.currentKey).isEqualTo(TestStartKey)
-        assertThat(niaNavigationState.currentTopLevelKey).isEqualTo(TestStartKey)
-    }
-
-    @Test
-    fun throwOnEmptyBackStack() {
-        assertFailsWith<IllegalStateException> {
-            niaNavigator.pop()
-        }
-    }
-}
-
-private object TestStartKey : NiaNavKey {
-    override val isTopLevel: Boolean
-        get() = true
-}
-
-private object TestTopLevelKey : NiaNavKey {
-    override val isTopLevel: Boolean
-        get() = true
-}
-
-private object TestKeyFirst : NiaNavKey {
-    override val isTopLevel: Boolean
-        get() = false
-}
-
-private object TestKeySecond : NiaNavKey {
-    override val isTopLevel: Boolean
-        get() = false
-}

feature/bookmarks/impl/src/main/kotlin/com/google/samples/apps/nowinandroid/feature/bookmarks/impl/navigation/BookmarksEntryProvider.kt

@@ -22,33 +22,16 @@ import androidx.compose.material3.SnackbarResult.ActionPerformed
 import androidx.compose.runtime.compositionLocalOf
 import androidx.navigation3.runtime.EntryProviderScope
 import androidx.navigation3.runtime.NavKey
-import com.google.samples.apps.nowinandroid.core.navigation.simple.Navigator
+import com.google.samples.apps.nowinandroid.core.navigation.Navigator
 import com.google.samples.apps.nowinandroid.feature.bookmarks.api.navigation.BookmarksRoute
 import com.google.samples.apps.nowinandroid.feature.bookmarks.impl.BookmarksScreen
-import com.google.samples.apps.nowinandroid.feature.topic.api.navigation.TopicRoute
+import com.google.samples.apps.nowinandroid.feature.topic.api.navigation.navigateToTopic
-//import com.google.samples.apps.nowinandroid.feature.topic.api.navigation.navigateToTopic
-import dagger.Module
-import dagger.Provides
-import dagger.hilt.InstallIn
-import dagger.hilt.android.components.ActivityComponent
-import dagger.multibindings.IntoSet
-
-@Module
-@InstallIn(ActivityComponent::class)
-object BookmarksEntryProvider {
-
-    @Provides
-    @IntoSet
-    fun provideBookmarksEntryProviderBuilder(
-        navigator: Navigator,
-    ): EntryProviderScope<NavKey>.() -> Unit = { bookmarksEntry(navigator) }
-}
 
 fun EntryProviderScope<NavKey>.bookmarksEntry(navigator: Navigator) {
     entry<BookmarksRoute> {
         val snackbarHostState = LocalSnackbarHostState.current
         BookmarksScreen(
-            onTopicClick = { topicId -> navigator.navigate(TopicRoute(topicId)) },
+            onTopicClick = navigator::navigateToTopic,
             onShowSnackbar = { message, action ->
                 snackbarHostState.showSnackbar(
                     message = message,

feature/bookmarks/impl/src/main/kotlin/com/google/samples/apps/nowinandroid/feature/bookmarks/impl/navigation/BookmarksSerializerModule.kt

@@ -1,42 +0,0 @@
-/*
- * Copyright 2025 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.bookmarks.impl.navigation
-
-import com.google.samples.apps.nowinandroid.core.navigation.NiaNavKey
-import com.google.samples.apps.nowinandroid.feature.bookmarks.api.navigation.BookmarksRoute
-import dagger.Module
-import dagger.Provides
-import dagger.hilt.InstallIn
-import dagger.hilt.components.SingletonComponent
-import dagger.multibindings.IntoSet
-import kotlinx.serialization.modules.PolymorphicModuleBuilder
-
-/**
- * Provides the DSL to register the route's [kotlinx.serialization.KSerializer] as a polymorphic serializer
- *
- */
-/*
-@Module
-@InstallIn(SingletonComponent::class)
-object BookmarksSerializerModule {
-    @Provides
-    @IntoSet
-    fun provideBookmarksPolymorphicModuleBuilder(): PolymorphicModuleBuilder<@JvmSuppressWildcards NiaNavKey>.() -> Unit = {
-        subclass(BookmarksRoute::class, BookmarksRoute.serializer())
-    }
-}
-*/

feature/foryou/impl/src/main/kotlin/com/google/samples/apps/nowinandroid/feature/foryou/impl/navigation/ForYouEntryProvider.kt

@@ -18,35 +18,15 @@ package com.google.samples.apps.nowinandroid.feature.foryou.impl.navigation
 
 import androidx.navigation3.runtime.EntryProviderScope
 import androidx.navigation3.runtime.NavKey
-import com.google.samples.apps.nowinandroid.core.navigation.simple.Navigator
+import com.google.samples.apps.nowinandroid.core.navigation.Navigator
 import com.google.samples.apps.nowinandroid.feature.foryou.api.navigation.ForYouRoute
 import com.google.samples.apps.nowinandroid.feature.foryou.impl.ForYouScreen
-import com.google.samples.apps.nowinandroid.feature.topic.api.navigation.TopicRoute
+import com.google.samples.apps.nowinandroid.feature.topic.api.navigation.navigateToTopic
-//import com.google.samples.apps.nowinandroid.feature.topic.api.navigation.navigateToTopic
-import dagger.Module
-import dagger.Provides
-import dagger.hilt.InstallIn
-import dagger.hilt.android.components.ActivityComponent
-import dagger.multibindings.IntoSet
-
-@Module
-@InstallIn(ActivityComponent::class)
-object ForYouEntryProvider {
-    /**
-     *  The ForYou composable for the app. It can also display information about topics.
-     *  This should be supplied from a separate module.
-     */
-    @Provides
-    @IntoSet
-    fun provideForYouEntryProviderBuilder(
-        navigator: Navigator,
-    ): EntryProviderScope<NavKey>.() -> Unit = { forYouEntry(navigator) }
-}
 
 fun EntryProviderScope<NavKey>.forYouEntry(navigator: Navigator) {
     entry<ForYouRoute> {
         ForYouScreen(
-            onTopicClick = { topicId -> navigator.navigate(TopicRoute(topicId)) },
+            onTopicClick = navigator::navigateToTopic,
         )
     }
 }

feature/foryou/impl/src/main/kotlin/com/google/samples/apps/nowinandroid/feature/foryou/impl/navigation/ForYouRouteSerializerModule.kt

@@ -1,42 +0,0 @@
-/*
- * Copyright 2025 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.foryou.impl.navigation
-
-import com.google.samples.apps.nowinandroid.core.navigation.NiaNavKey
-import com.google.samples.apps.nowinandroid.feature.foryou.api.navigation.ForYouRoute
-import dagger.Module
-import dagger.Provides
-import dagger.hilt.InstallIn
-import dagger.hilt.components.SingletonComponent
-import dagger.multibindings.IntoSet
-import kotlinx.serialization.modules.PolymorphicModuleBuilder
-
-/**
- * Provides the DSL to register the route's [kotlinx.serialization.KSerializer] as a polymorphic serializer
- *
- */
-/*
-@Module
-@InstallIn(SingletonComponent::class)
-object ForYouRouteSerializerModule {
-    @Provides
-    @IntoSet
-    fun provideForYouPolymorphicModuleBuilder(): PolymorphicModuleBuilder<@JvmSuppressWildcards NiaNavKey>.() -> Unit = {
-        subclass(ForYouRoute::class, ForYouRoute.serializer())
-    }
-}
-*/

feature/interests/impl/src/main/kotlin/com/google/samples/apps/nowinandroid/feature/interests/impl/navigation/InterestsEntryProvider.kt

@@ -21,12 +21,13 @@ import androidx.compose.material3.adaptive.navigation3.ListDetailSceneStrategy
 import androidx.hilt.lifecycle.viewmodel.compose.hiltViewModel
 import androidx.navigation3.runtime.EntryProviderScope
 import androidx.navigation3.runtime.NavKey
-import com.google.samples.apps.nowinandroid.core.navigation.simple.Navigator
+import com.google.samples.apps.nowinandroid.core.navigation.Navigator
 import com.google.samples.apps.nowinandroid.feature.interests.api.navigation.InterestsRoute
 import com.google.samples.apps.nowinandroid.feature.interests.impl.InterestsDetailPlaceholder
 import com.google.samples.apps.nowinandroid.feature.interests.impl.InterestsScreen
 import com.google.samples.apps.nowinandroid.feature.interests.impl.InterestsViewModel
 import com.google.samples.apps.nowinandroid.feature.topic.api.navigation.TopicRoute
+import com.google.samples.apps.nowinandroid.feature.topic.api.navigation.navigateToTopic
 //import com.google.samples.apps.nowinandroid.feature.topic.api.navigation.navigateToTopic
 import dagger.Module
 import dagger.Provides
@@ -57,9 +58,8 @@ fun EntryProviderScope<NavKey>.interestsEntry(navigator: Navigator) {
             it.create(key)
         }
         InterestsScreen(
-            // TODO: This event should be provided by the ViewModel
+            // TODO: This event should either be provided by the ViewModel or by the navigator, not both
-            // TODO: This could be made into an extension function on navigator
+            onTopicClick = navigator::navigateToTopic,
-            onTopicClick = { topicId -> navigator.navigate(TopicRoute(topicId)) },
 
             // TODO: This should be dynamically calculated based on the rendering scene
             //  See https://github.com/android/nav3-recipes/commit/488f4811791ca3ed7192f4fe3c86e7371b32ebdc#diff-374e02026cdd2f68057dd940f203dc4ba7319930b33e9555c61af7e072211cabR89

feature/interests/impl/src/main/kotlin/com/google/samples/apps/nowinandroid/feature/interests/impl/navigation/InterestsSerializerModule.kt

@@ -1,42 +0,0 @@
-/*
- * Copyright 2025 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.interests.impl.navigation
-
-import com.google.samples.apps.nowinandroid.core.navigation.NiaNavKey
-import com.google.samples.apps.nowinandroid.feature.interests.api.navigation.InterestsRoute
-import dagger.Module
-import dagger.Provides
-import dagger.hilt.InstallIn
-import dagger.hilt.components.SingletonComponent
-import dagger.multibindings.IntoSet
-import kotlinx.serialization.modules.PolymorphicModuleBuilder
-
-/**
- * Provides the DSL to register the route's [kotlinx.serialization.KSerializer] as a polymorphic serializer
- *
- */
-/*
-@Module
-@InstallIn(SingletonComponent::class)
-object InterestsSerializerModule {
-    @Provides
-    @IntoSet
-    fun provideInterestsPolymorphicModuleBuilder(): PolymorphicModuleBuilder<@JvmSuppressWildcards NiaNavKey>.() -> Unit = {
-        subclass(InterestsRoute::class, InterestsRoute.serializer())
-    }
-}
-*/

feature/search/api/src/main/kotlin/com/google/samples/apps/nowinandroid/feature/search/api/navigation/SearchRoute.kt

@@ -17,21 +17,7 @@
 package com.google.samples.apps.nowinandroid.feature.search.api.navigation
 
 import androidx.navigation3.runtime.NavKey
-import com.google.samples.apps.nowinandroid.core.navigation.NiaNavKey
-import com.google.samples.apps.nowinandroid.core.navigation.NiaNavigator
 import kotlinx.serialization.Serializable
 
-/*
-@Serializable
-object SearchRoute : NiaNavKey {
-    override val isTopLevel: Boolean
-        get() = false
-}
-
-fun NiaNavigator.navigateToSearch() {
-    navigate(SearchRoute)
-}
-*/
-
 @Serializable
 object SearchRoute : NavKey

feature/search/impl/src/main/kotlin/com/google/samples/apps/nowinandroid/feature/search/impl/navigation/SearchEntryProvider.kt

@@ -18,34 +18,18 @@ package com.google.samples.apps.nowinandroid.feature.search.impl.navigation
 
 import androidx.navigation3.runtime.EntryProviderScope
 import androidx.navigation3.runtime.NavKey
-import com.google.samples.apps.nowinandroid.core.navigation.simple.Navigator
+import com.google.samples.apps.nowinandroid.core.navigation.Navigator
 import com.google.samples.apps.nowinandroid.feature.interests.api.navigation.InterestsRoute
 import com.google.samples.apps.nowinandroid.feature.search.api.navigation.SearchRoute
 import com.google.samples.apps.nowinandroid.feature.search.impl.SearchScreen
-import com.google.samples.apps.nowinandroid.feature.topic.api.navigation.TopicRoute
+import com.google.samples.apps.nowinandroid.feature.topic.api.navigation.navigateToTopic
-import dagger.Module
-import dagger.Provides
-import dagger.hilt.InstallIn
-import dagger.hilt.android.components.ActivityComponent
-import dagger.multibindings.IntoSet
-
-@Module
-@InstallIn(ActivityComponent::class)
-object SearchEntryProvider {
-
-    @Provides
-    @IntoSet
-    fun provideSearchEntryProviderBuilder(
-        navigator: Navigator,
-    ): EntryProviderScope<NavKey>.() -> Unit = { searchEntry(navigator) }
-}
 
 fun EntryProviderScope<NavKey>.searchEntry(navigator: Navigator) {
-    entry<SearchRoute> { key ->
+    entry<SearchRoute> {
         SearchScreen(
             onBackClick = { navigator.goBack() },
             onInterestsClick = { navigator.navigate(InterestsRoute()) },
-            onTopicClick = { topicId -> navigator.navigate(TopicRoute(topicId)) },
+            onTopicClick = navigator::navigateToTopic,
         )
     }
 }

feature/search/impl/src/main/kotlin/com/google/samples/apps/nowinandroid/feature/search/impl/navigation/SearchSerializerModule.kt

@@ -1,40 +0,0 @@
-/*
- * Copyright 2025 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.search.impl.navigation
-
-import com.google.samples.apps.nowinandroid.core.navigation.NiaNavKey
-import com.google.samples.apps.nowinandroid.feature.search.api.navigation.SearchRoute
-import dagger.Module
-import dagger.Provides
-import dagger.hilt.InstallIn
-import dagger.hilt.components.SingletonComponent
-import dagger.multibindings.IntoSet
-import kotlinx.serialization.modules.PolymorphicModuleBuilder
-
-/**
- * Provides the DSL to register the route's [kotlinx.serialization.KSerializer] as a polymorphic serializer
- *
- */
-/*@Module
-@InstallIn(SingletonComponent::class)
-object SearchSerializerModule {
-    @Provides
-    @IntoSet
-    fun provideSearchPolymorphicModuleBuilder(): PolymorphicModuleBuilder<@JvmSuppressWildcards NiaNavKey>.() -> Unit = {
-        subclass(SearchRoute::class, SearchRoute.serializer())
-    }
-}*/

feature/topic/api/src/main/kotlin/com/google/samples/apps/nowinandroid/feature/topic/api/navigation/TopicRoute.kt

@@ -17,23 +17,14 @@
 package com.google.samples.apps.nowinandroid.feature.topic.api.navigation
 
 import androidx.navigation3.runtime.NavKey
-import com.google.samples.apps.nowinandroid.core.navigation.NiaNavKey
+import com.google.samples.apps.nowinandroid.core.navigation.Navigator
-import com.google.samples.apps.nowinandroid.core.navigation.NiaNavigator
 import kotlinx.serialization.Serializable
 
-/*
 @Serializable
-data class TopicRoute(val id: String) : NiaNavKey {
+data class TopicRoute(val id: String) : NavKey
-    override val isTopLevel: Boolean
-        get() = false
-}
 
-fun NiaNavigator.navigateToTopic(
+fun Navigator.navigateToTopic(
     topicId: String,
 ) {
     navigate(TopicRoute(topicId))
 }
-*/
-
-@Serializable
-data class TopicRoute(val id: String) : NavKey

feature/topic/api/src/main/kotlin/com/google/samples/apps/nowinandroid/feature/topic/api/navigation/TopicSerializerModule.kt

@@ -1,39 +0,0 @@
-/*
- * Copyright 2025 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.topic.api.navigation
-
-import com.google.samples.apps.nowinandroid.core.navigation.NiaNavKey
-import dagger.Module
-import dagger.Provides
-import dagger.hilt.InstallIn
-import dagger.hilt.components.SingletonComponent
-import dagger.multibindings.IntoSet
-import kotlinx.serialization.modules.PolymorphicModuleBuilder
-
-/**
- * Provides the DSL to register the route's [kotlinx.serialization.KSerializer] as a polymorphic serializer
- *
- */
-/*@Module
-@InstallIn(SingletonComponent::class)
-object TopicSerializerModule {
-    @Provides
-    @IntoSet
-    fun provideTopicPolymorphicModuleBuilder(): PolymorphicModuleBuilder<@JvmSuppressWildcards NiaNavKey>.() -> Unit = {
-        subclass(TopicRoute::class, TopicRoute.serializer())
-    }
-}*/

feature/topic/impl/src/main/kotlin/com/google/samples/apps/nowinandroid/feature/topic/impl/navigation/TopicEntryProvider.kt

@@ -21,29 +21,12 @@ import androidx.compose.material3.adaptive.navigation3.ListDetailSceneStrategy
 import androidx.hilt.lifecycle.viewmodel.compose.hiltViewModel
 import androidx.navigation3.runtime.EntryProviderScope
 import androidx.navigation3.runtime.NavKey
-import com.google.samples.apps.nowinandroid.core.navigation.simple.Navigator
+import com.google.samples.apps.nowinandroid.core.navigation.Navigator
 import com.google.samples.apps.nowinandroid.feature.topic.api.navigation.TopicRoute
-//import com.google.samples.apps.nowinandroid.feature.topic.api.navigation.navigateToTopic
+import com.google.samples.apps.nowinandroid.feature.topic.api.navigation.navigateToTopic
 import com.google.samples.apps.nowinandroid.feature.topic.impl.TopicScreen
 import com.google.samples.apps.nowinandroid.feature.topic.impl.TopicViewModel
 import com.google.samples.apps.nowinandroid.feature.topic.impl.TopicViewModel.Factory
-import dagger.Module
-import dagger.Provides
-import dagger.hilt.InstallIn
-import dagger.hilt.android.components.ActivityComponent
-import dagger.multibindings.IntoSet
-
-@Module
-@InstallIn(ActivityComponent::class)
-object TopicEntryProvider {
-
-    @OptIn(ExperimentalMaterial3AdaptiveApi::class)
-    @Provides
-    @IntoSet
-    fun provideTopicEntryProviderBuilder(
-        navigator: Navigator,
-    ): EntryProviderScope<NavKey>.() -> Unit = { topicEntry(navigator) }
-}
 
 @OptIn(ExperimentalMaterial3AdaptiveApi::class)
 fun EntryProviderScope<NavKey>.topicEntry(navigator: Navigator) {
@@ -54,7 +37,7 @@ fun EntryProviderScope<NavKey>.topicEntry(navigator: Navigator) {
         TopicScreen(
             showBackButton = true,
             onBackClick = { navigator.goBack() },
-            onTopicClick = { topicId -> navigator.navigate(TopicRoute(topicId)) },
+            onTopicClick = navigator::navigateToTopic,
             viewModel = hiltViewModel<TopicViewModel, Factory>(
                 key = id,
             ) { factory ->