Fix issues when the system kills the app during playback (#1116)

## Description
This fixes some issues restoring the app state after it is killed by the
system, such as to free up memory while the screensaver is showing.

### Dev notes

Reproduce:
1. Start playing media from beginning
2. Pause at 10 minute mark
3. Wait for screensaver to start
4. Press a button
5. Media starts from beginning

Note: It may take a few iterations of 2-4 before the OS destroys the
app.

If the app is killed during playback, ideally Wholphin restores state to
_previous_ page, not playback since restoring playback is complex.
Before this PR, the back stack was maintained by Compose's
`rememberSerializable` and would be restored _after_ the
`PlaybackLifecycleObserver` cleans up the playback destination.

This meant that the app would be restored, from scratch, to the playback
page. The `PlaybackViewModel` would be initialized from scratch as it
was originally called, ie play from beginning.

The fix is to save and restore the back stack outside of Compose.

### Related issues
Fixes #767

### Testing
Emulator & nvidia shield

## Screenshots
N/A

## AI or LLM usage
None

app/src/androidTest/java/com/github/damontecres/wholphin/test/InstrumentedBasicUiTests.kt

@@ -9,7 +9,9 @@ import androidx.compose.ui.test.onNodeWithTag
 import androidx.compose.ui.test.onNodeWithText
 import androidx.compose.ui.test.performKeyInput
 import androidx.compose.ui.test.pressKey
+import androidx.navigation3.runtime.NavBackStack
 import com.github.damontecres.wholphin.MainContent
+import com.github.damontecres.wholphin.services.NavigationManager
 import com.github.damontecres.wholphin.services.ScreensaverService
 import com.github.damontecres.wholphin.services.ScreensaverState
 import com.github.damontecres.wholphin.services.SetupDestination
@@ -43,16 +45,17 @@ class InstrumentedBasicUiTests {
     @OptIn(ExperimentalTestApi::class)
     @Test
     fun myTest() {
+        val navigationManager = NavigationManager()
+        navigationManager.backStack = NavBackStack(Destination.Home())
         // Start the app
         composeTestRule.setContent {
             WholphinTheme {
                 MainContent(
                     backStack = mutableListOf(SetupDestination.ServerList),
-                    navigationManager = mockk(relaxed = true),
+                    navigationManager = navigationManager,
                     appPreferences = mockk(relaxed = true),
                     backdropService = mockk(relaxed = true),
                     screensaverService = screensaverService,
-                    requestedDestination = Destination.Home(),
                     modifier = Modifier,
                 )
             }

app/src/main/java/com/github/damontecres/wholphin/MainActivity.kt

@@ -24,6 +24,7 @@ import androidx.datastore.core.DataStore
 import androidx.lifecycle.ViewModel
 import androidx.lifecycle.lifecycleScope
 import androidx.lifecycle.viewModelScope
+import androidx.navigation3.runtime.NavBackStack
 import androidx.tv.material3.ExperimentalTvMaterial3Api
 import com.github.damontecres.wholphin.data.ServerRepository
 import com.github.damontecres.wholphin.preferences.AppPreference
@@ -67,6 +68,7 @@ import kotlinx.coroutines.flow.launchIn
 import kotlinx.coroutines.flow.onEach
 import kotlinx.coroutines.launch
 import kotlinx.coroutines.withContext
+import kotlinx.serialization.json.Json
 import okhttp3.OkHttpClient
 import org.jellyfin.sdk.model.api.BaseItemKind
 import org.jellyfin.sdk.model.serializer.toUUIDOrNull
@@ -127,6 +129,11 @@ class MainActivity : AppCompatActivity() {
 
     private var signInAuto = true
 
+    private val json =
+        Json {
+            classDiscriminator = "_type"
+        }
+
     @OptIn(ExperimentalTvMaterial3Api::class)
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
@@ -134,6 +141,23 @@ class MainActivity : AppCompatActivity() {
         Timber.i("MainActivity.onCreate: savedInstanceState is null=${savedInstanceState == null}")
         lifecycle.addObserver(playbackLifecycleObserver)
 
+        val backStackStr = savedInstanceState?.getString(KEY_BACK_STACK)
+        if (backStackStr != null) {
+            Timber.d("Restoring back stack")
+            var backStack = json.decodeFromString<List<Destination>>(backStackStr)
+            val lastDest = backStack.lastOrNull()
+            if (lastDest is Destination.Playback ||
+                lastDest is Destination.PlaybackList ||
+                lastDest is Destination.Slideshow
+            ) {
+                backStack = backStack.toMutableList().apply { removeAt(lastIndex) }
+            }
+            navigationManager.backStack = NavBackStack(*backStack.toTypedArray())
+        } else {
+            val startDestination = intent?.let(::extractDestination) ?: Destination.Home()
+            navigationManager.backStack = NavBackStack(startDestination)
+        }
+
         viewModel.serverRepository.currentUser.observe(this) { user ->
             if (user?.hasPin == true) {
                 window?.setFlags(
@@ -206,17 +230,12 @@ class MainActivity : AppCompatActivity() {
                         appThemeColors = appPreferences.interfacePreferences.appThemeColors,
                     ) {
                         ProvideLocalClock {
-                            val requestedDestination =
-                                remember(intent) {
-                                    intent?.let(::extractDestination) ?: Destination.Home()
-                                }
                             MainContent(
                                 backStack = setupNavigationManager.backStack,
                                 navigationManager = navigationManager,
                                 appPreferences = appPreferences,
                                 backdropService = backdropService,
                                 screensaverService = screensaverService,
-                                requestedDestination = requestedDestination,
                                 modifier = Modifier.fillMaxSize(),
                             )
                         }
@@ -287,6 +306,8 @@ class MainActivity : AppCompatActivity() {
     override fun onSaveInstanceState(outState: Bundle) {
         super.onSaveInstanceState(outState)
         Timber.d("onSaveInstanceState")
+        val str = json.encodeToString(navigationManager.backStack.toList())
+        outState.putString(KEY_BACK_STACK, str)
     }
 
     override fun onRestoreInstanceState(savedInstanceState: Bundle) {
@@ -362,6 +383,8 @@ class MainActivity : AppCompatActivity() {
         const val INTENT_SEASON_NUMBER = "seaNum"
         const val INTENT_SEASON_ID = "seaId"
 
+        private const val KEY_BACK_STACK = "backStack"
+
         lateinit var instance: MainActivity
             private set
     }

app/src/main/java/com/github/damontecres/wholphin/MainContent.kt

@@ -33,10 +33,8 @@ import com.github.damontecres.wholphin.services.ScreensaverService
 import com.github.damontecres.wholphin.services.SetupDestination
 import com.github.damontecres.wholphin.ui.components.AppScreensaver
 import com.github.damontecres.wholphin.ui.nav.ApplicationContent
-import com.github.damontecres.wholphin.ui.nav.Destination
 import com.github.damontecres.wholphin.ui.setup.SwitchServerContent
 import com.github.damontecres.wholphin.ui.setup.SwitchUserContent
-import com.github.damontecres.wholphin.ui.util.ProvideLocalClock
 
 @Composable
 fun MainContent(
@@ -45,7 +43,6 @@ fun MainContent(
     appPreferences: AppPreferences,
     backdropService: BackdropService,
     screensaverService: ScreensaverService,
-    requestedDestination: Destination,
     modifier: Modifier = Modifier,
 ) {
     Surface(
@@ -113,7 +110,6 @@ fun MainContent(
                                 ApplicationContent(
                                     user = current.user,
                                     server = current.server,
-                                    startDestination = requestedDestination,
                                     navigationManager = navigationManager,
                                     preferences = preferences,
                                     modifier = Modifier.fillMaxSize(),

app/src/main/java/com/github/damontecres/wholphin/WholphinDreamService.kt

@@ -22,9 +22,7 @@ import androidx.savedstate.SavedStateRegistryOwner
 import androidx.savedstate.setViewTreeSavedStateRegistryOwner
 import com.github.damontecres.wholphin.data.ServerRepository
 import com.github.damontecres.wholphin.preferences.AppPreferences
-import com.github.damontecres.wholphin.preferences.UserPreferences
 import com.github.damontecres.wholphin.services.ScreensaverService
-import com.github.damontecres.wholphin.services.UserPreferencesService
 import com.github.damontecres.wholphin.ui.components.AppScreensaverContent
 import com.github.damontecres.wholphin.ui.launchDefault
 import com.github.damontecres.wholphin.ui.theme.WholphinTheme
@@ -33,6 +31,7 @@ import dagger.hilt.android.AndroidEntryPoint
 import kotlinx.coroutines.flow.collectLatest
 import kotlinx.coroutines.flow.first
 import org.jellyfin.sdk.model.serializer.toUUIDOrNull
+import timber.log.Timber
 import javax.inject.Inject
 import kotlin.time.Duration.Companion.milliseconds
 
@@ -61,6 +60,7 @@ class WholphinDreamService :
 
     override fun onCreate() {
         super.onCreate()
+        Timber.d("onCreate")
 
         savedStateRegistryController.performRestore(null)
         lifecycleRegistry.currentState = Lifecycle.State.CREATED
@@ -74,6 +74,7 @@ class WholphinDreamService :
 
     override fun onAttachedToWindow() {
         super.onAttachedToWindow()
+        Timber.d("onAttachedToWindow")
         val itemFlow = screensaverService.createItemFlow(lifecycleScope)
         setContentView(
             ComposeView(this).apply {
@@ -109,11 +110,13 @@ class WholphinDreamService :
 
     override fun onDreamingStarted() {
         super.onDreamingStarted()
+        Timber.d("onDreamingStarted")
         lifecycleRegistry.currentState = Lifecycle.State.STARTED
     }
 
     override fun onDreamingStopped() {
         super.onDreamingStopped()
+        Timber.d("onDreamingStopped")
         lifecycleRegistry.currentState = Lifecycle.State.DESTROYED
     }
 }

app/src/main/java/com/github/damontecres/wholphin/services/NavigationManager.kt

@@ -1,6 +1,5 @@
 package com.github.damontecres.wholphin.services
 
-import androidx.navigation3.runtime.NavKey
 import com.github.damontecres.wholphin.ui.nav.Destination
 import org.acra.ACRA
 import timber.log.Timber
@@ -14,7 +13,7 @@ import javax.inject.Singleton
 class NavigationManager
     @Inject
     constructor() {
-        var backStack: MutableList<NavKey> = mutableListOf()
+        var backStack: MutableList<Destination> = mutableListOf()
 
         /**
          * Go to the specified [com.github.damontecres.wholphin.ui.nav.Destination]

app/src/main/java/com/github/damontecres/wholphin/ui/nav/ApplicationContent.kt

@@ -9,7 +9,6 @@ import androidx.compose.foundation.layout.fillMaxWidth
 import androidx.compose.foundation.lazy.rememberLazyListState
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.getValue
-import androidx.compose.runtime.saveable.rememberSerializable
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.draw.drawBehind
@@ -28,12 +27,8 @@ import androidx.lifecycle.ViewModel
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import androidx.lifecycle.viewModelScope
 import androidx.lifecycle.viewmodel.navigation3.rememberViewModelStoreNavEntryDecorator
-import androidx.navigation3.runtime.NavBackStack
 import androidx.navigation3.runtime.NavEntry
-import androidx.navigation3.runtime.NavKey
 import androidx.navigation3.runtime.rememberSaveableStateHolderNavEntryDecorator
-import androidx.navigation3.runtime.serialization.NavBackStackSerializer
-import androidx.navigation3.runtime.serialization.NavKeySerializer
 import androidx.navigation3.ui.NavDisplay
 import androidx.tv.material3.DrawerValue
 import androidx.tv.material3.MaterialTheme
@@ -78,22 +73,12 @@ class ApplicationContentViewModel
 fun ApplicationContent(
     server: JellyfinServer,
     user: JellyfinUser,
-    startDestination: Destination,
     navigationManager: NavigationManager,
     preferences: UserPreferences,
     modifier: Modifier = Modifier,
     enableTopScrim: Boolean = true,
     viewModel: ApplicationContentViewModel = hiltViewModel(),
 ) {
-    val backStack: MutableList<NavKey> =
-        rememberSerializable(
-            server,
-            user,
-            serializer = NavBackStackSerializer(elementSerializer = NavKeySerializer()),
-        ) {
-            NavBackStack(startDestination)
-        }
-    navigationManager.backStack = backStack
     val backdrop by viewModel.backdropService.backdropFlow.collectAsStateWithLifecycle()
     val backdropStyle = preferences.appPreferences.interfacePreferences.backdropStyle
     val drawerState = rememberDrawerState(DrawerValue.Closed)