AuthGraph.kt: Separate auth-gateway destinations to dedicated nested NavGraph

* This fixes the issue where navigating to
  the nested AuthDestination.Login route
  causes a runtime crash as navigating to
  nested NavGraph routes is not possible
  (this is apparently "Intended Behaviour" -
  see https://issuetracker.google.com/issues/357896945)
* Add separate `AuthGatewayGraphRoot`
  destination
  * Add `navigateToAuthGatewayGraph` DSL
* Remove `isLoggedIn` checks from
  `authGraph` NavGraph

Author: EdricChan03

app/src/main/java/com/edricchan/studybuddy/navigation/compat/CompatNavigation.kt

@@ -47,8 +47,7 @@ fun NavGraphBuilder.aboutGraph(
  */
 // TODO: Migrate destinations to Jetpack Compose
 fun NavGraphBuilder.compatGraphs(
-    context: Context,
-    isLoggedIn: Boolean
+    context: Context
 ) {
     activity<CompatDestination.Debug> {
         activityClass = DebugActivity::class
@@ -68,7 +67,7 @@ fun NavGraphBuilder.compatGraphs(
 
     aboutGraph(context = context)
     context(context) {
-        authGraph(isLoggedIn = isLoggedIn)
+        authGraph()
         taskGraph()
     }
 

app/src/main/java/com/edricchan/studybuddy/ui/modules/main/MainActivity.kt

@@ -315,11 +315,10 @@ class MainActivity : BaseActivity(), NavController.OnDestinationChangedListener
         val isLoggedIn = auth.currentUser != null
         graph = createGraph(
             if (isLoggedIn) TaskDestination.TaskGraphRoot
-            else AuthDestination.Login
+            else AuthDestination.AuthGatewayGraphRoot
         ) {
             compatGraphs(
-                context = this@MainActivity,
-                isLoggedIn = isLoggedIn
+                context = this@MainActivity
             )
         }
 

features/auth/navigation/src/main/kotlin/com/edricchan/studybuddy/features/auth/navigation/AuthDestination.kt

@@ -13,6 +13,10 @@ sealed interface AuthDestination {
     @Serializable
     data object AuthGraphRoot : AuthDestination
 
+    /** Root destination for all gateway-related destinations in the authentication graph. */
+    @Serializable
+    data object AuthGatewayGraphRoot : AuthDestination
+
     /** Destination to view the currently signed-in user's information. */
     @Serializable
     data class AccountInfo(val action: AccountAction? = null) : AuthDestination {

features/auth/navigation/src/main/kotlin/com/edricchan/studybuddy/features/auth/navigation/AuthNavigation.kt

@@ -17,6 +17,16 @@ fun NavController.navigateToAuthGraph(
     builder: NavOptionsBuilder.() -> Unit = DefaultNavOptionsBuilder
 ) = navigate(AuthDestination.AuthGraphRoot, builder)
 
+/**
+ * Navigates to the [AuthDestination.AuthGatewayGraphRoot] route.
+ *
+ * By default, [NavOptionsBuilder.launchSingleTop] is set to `true`. If this
+ * behaviour is undesired, [builder] should be specified.
+ */
+fun NavController.navigateToAuthGatewayGraph(
+    builder: NavOptionsBuilder.() -> Unit = DefaultNavOptionsBuilder
+) = navigate(AuthDestination.AuthGatewayGraphRoot, builder)
+
 /**
  * Navigates to the [AuthDestination.AccountInfo] route.
  *

features/auth/src/main/kotlin/com/edricchan/studybuddy/features/auth/navigation/graph/AuthGraph.kt

@@ -18,26 +18,30 @@ import com.edricchan.studybuddy.features.auth.navigation.R as NavR
  * @see AuthDestination
  */
 context(context: Context)
-fun NavGraphBuilder.authGraph(
-    isLoggedIn: Boolean
-) = navigation<AuthDestination.AuthGraphRoot>(
-    startDestination = if (isLoggedIn) AuthDestination.AccountInfo() else AuthDestination.Login
-) {
-    fragment<AccountFragment, AuthDestination.AccountInfo>(
-        typeMap = mapOf(typeOf<AuthDestination.AccountInfo.AccountAction>() to AuthDestination.AccountInfo.AccountAction.NavType)
+fun NavGraphBuilder.authGraph() {
+    navigation<AuthDestination.AuthGraphRoot>(
+        startDestination = AuthDestination.AccountInfo()
     ) {
-        label = context.getString(NavR.string.nav_auth_dest_account_info_label)
+        fragment<AccountFragment, AuthDestination.AccountInfo>(
+            typeMap = mapOf(typeOf<AuthDestination.AccountInfo.AccountAction>() to AuthDestination.AccountInfo.AccountAction.NavType)
+        ) {
+            label = context.getString(NavR.string.nav_auth_dest_account_info_label)
+        }
     }
 
-    fragment<LoginFragment, AuthDestination.Login> {
-        label = context.getString(NavR.string.nav_auth_dest_login_label)
-    }
+    navigation<AuthDestination.AuthGatewayGraphRoot>(
+        startDestination = AuthDestination.Login
+    ) {
+        fragment<LoginFragment, AuthDestination.Login> {
+            label = context.getString(NavR.string.nav_auth_dest_login_label)
+        }
 
-    fragment<RegisterFragment, AuthDestination.Register> {
-        label = context.getString(NavR.string.nav_auth_dest_register_label)
-    }
+        fragment<RegisterFragment, AuthDestination.Register> {
+            label = context.getString(NavR.string.nav_auth_dest_register_label)
+        }
 
-    fragment<RecoveryFragment, AuthDestination.Recovery> {
-        label = context.getString(NavR.string.nav_auth_dest_recover_account_label)
+        fragment<RecoveryFragment, AuthDestination.Recovery> {
+            label = context.getString(NavR.string.nav_auth_dest_recover_account_label)
+        }
     }
 }