✨ New: Sign in anonymously (#80)

* Add signInAnonymously method to SessionCubit

* Add spacing and "Continue as guest" button to
AuthPage

* Add Google account linking functionality to
SessionCubit

* Add isGuest property to Authenticated state

* Add "Continue as guest" button functionality

* Add Google account linking and sign out
functionality

* Fix stream subscription in user library and recent
media services

* Add forceLogin parameter to redirect logic in
routerConfig

* Fix authentication bugs and add email account
linking

* Add import for flutter/scheduler.dart

* Refactor router configuration

* Refactor session_cubit.dart to update display name
if provided

* Add AppSnackbar to show success message after
account linking

* Fix authentication flow and update routes

lib/features/session/cubit/session_cubit.dart

@@ -65,8 +65,32 @@ class SessionCubit extends AppCubit<SessionState> {
       final userCredential = await _auth.signInWithCredential(credential);
       _logger.d(userCredential.user?.toString());
     } on FirebaseAuthException catch (e) {
+      emit(UnAuthenticated());
       _handleException(e);
     } catch (e) {
+      await _googleSignIn.signOut();
+      emit(UnAuthenticated());
+      _logger.d(e.toString());
+    }
+  }
+
+  Future<void> linkGoogleAccount() async {
+    final prevState = state;
+    try {
+      final account = await _googleSignIn.signIn();
+      final authentication = await account?.authentication;
+      final credential = GoogleAuthProvider.credential(
+        accessToken: authentication?.accessToken,
+        idToken: authentication?.idToken,
+      );
+      final user = _auth.currentUser;
+      await user?.linkWithCredential(credential);
+    } on FirebaseAuthException catch (e) {
+      emit(prevState);
+      await _googleSignIn.signOut();
+      _handleException(e);
+    } catch (e) {
+      emit(prevState);
       await _googleSignIn.signOut();
       _logger.d(e.toString());
     }
@@ -83,11 +107,40 @@ class SessionCubit extends AppCubit<SessionState> {
         password: password,
       );
       _logger.d(userCredential.user?.toString());
+    } on FirebaseAuthException catch (e) {
+      emit(UnAuthenticated());
+      _handleException(e);
+    } catch (e) {
+      emit(UnAuthenticated());
+      _logger.d(e.toString());
+    }
+  }
+
+  Future<bool> linkEmailPassword({
+    required String email,
+    required String password,
+    String? name,
+  }) async {
+    try {
+      final user = _auth.currentUser;
+      final credential = EmailAuthProvider.credential(
+        email: email,
+        password: password,
+      );
+      final ucredential = await user?.linkWithCredential(credential);
+      if (ucredential?.user != null) {
+        if (name != null) {
+          unawaited(ucredential?.user?.updateDisplayName(name));
+        }
+        emit((state as Authenticated).copyWith(user: ucredential!.user!));
+      }
+      return true;
     } on FirebaseAuthException catch (e) {
       _handleException(e);
     } catch (e) {
       _logger.d(e.toString());
     }
+    return false;
   }
 
   Future<void> signUpWithEmailAndPassword({
@@ -103,6 +156,20 @@ class SessionCubit extends AppCubit<SessionState> {
       );
       await userCredential.user?.updateDisplayName(name);
       _logger.d(userCredential.user?.toString());
+    } on FirebaseAuthException catch (e) {
+      emit(UnAuthenticated());
+      _handleException(e);
+    } catch (e) {
+      emit(UnAuthenticated());
+      _logger.d(e.toString());
+    }
+  }
+
+  Future<void> signInAnonymously() async {
+    emit(Authenticating());
+    try {
+      final userCredential = await _auth.signInAnonymously();
+      _logger.d(userCredential.user?.toString());
     } on FirebaseAuthException catch (e) {
       _handleException(e);
     } catch (e) {
@@ -146,6 +213,8 @@ class SessionCubit extends AppCubit<SessionState> {
       'operation-not-allowed' =>
         'Indicates that Email & Password accounts are not enabled.',
       'weak-password' => 'The password must be 6 characters long or more.',
+      'credential-already-in-use' =>
+        'This credential is already associated with a different user account.',
       (_) => 'An undefined Error happened.'
     };
     AppSnackbar.show(message);

lib/features/session/cubit/session_state.dart

@@ -64,4 +64,6 @@ final class Authenticated extends SessionState {
       userData: userData ?? this.userData,
     );
   }
+
+  bool get isGuest => user.isAnonymous;
 }

lib/features/session/ui/auth_page.dart

@@ -12,6 +12,8 @@ class AuthPage extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
+    final isGuest = context.select((SessionCubit cubit) =>
+        cubit.state is Authenticated && (cubit.state as Authenticated).isGuest);
     return Scaffold(
       body: SafeArea(
         child: Align(
@@ -22,6 +24,7 @@ class AuthPage extends StatelessWidget {
               mainAxisAlignment: MainAxisAlignment.center,
               crossAxisAlignment: CrossAxisAlignment.stretch,
               children: [
+                const Spacer(),
                 Assets.icon.appIconMonotone.svg(
                   placeholderBuilder: (ctx) =>
                       const SizedBox(width: 48, height: 48),
@@ -53,6 +56,18 @@ class AuthPage extends StatelessWidget {
                 TextButton(
                   onPressed: () => context.pushNamed(AppRoutes.login.name),
                   child: _buildText(context, "Log in"),
+                ),
+                const Spacer(),
+                Visibility(
+                  visible: !isGuest,
+                  child: TextButton(
+                    onPressed: () async {
+                      await context.read<SessionCubit>().signInAnonymously();
+                      if (!context.mounted) return;
+                      context.goNamed(AppRoutes.home.name);
+                    },
+                    child: _buildText(context, "Continue as guest", true),
+                  ),
                 )
               ],
             ),
@@ -68,10 +83,20 @@ class AuthPage extends StatelessWidget {
     );
   }
 
-  Text _buildText(BuildContext context, String text) {
+  Text _buildText(BuildContext context, String text,
+      [bool isUnderlined = false]) {
+    var style =
+        context.textTheme.bodyLarge?.copyWith(fontWeight: FontWeight.bold);
+    if (isUnderlined) {
+      style = style?.copyWith(
+        decoration: TextDecoration.underline,
+        decorationColor: Colors.white,
+        decorationThickness: 2,
+      );
+    }
     return Text(
       text,
-      style: context.textTheme.bodyLarge?.copyWith(fontWeight: FontWeight.bold),
+      style: style,
     );
   }
 }

lib/features/session/ui/login_page.dart

@@ -1,6 +1,8 @@
 import 'package:flutter/material.dart';
 import 'package:flutter_bloc/flutter_bloc.dart';
+import 'package:go_router/go_router.dart';
 import 'package:varanasi_mobile_app/features/session/cubit/session_cubit.dart';
+import 'package:varanasi_mobile_app/utils/app_snackbar.dart';
 import 'package:varanasi_mobile_app/utils/extensions/extensions.dart';
 import 'package:varanasi_mobile_app/widgets/input_field.dart';
 
@@ -142,15 +144,29 @@ class LoginButton extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
+    final isGuestUser = context.select((SessionCubit cubit) =>
+        cubit.state is Authenticated && (cubit.state as Authenticated).isGuest);
     return Align(
       alignment: Alignment.center,
       child: FilledButton.tonal(
         onPressed: isFormValid
-            ? () {
-                context.read<SessionCubit>().signInWithEmailAndPassword(
-                      email: _emailController.text,
-                      password: _passwordController.text,
-                    );
+            ? () async {
+                if (isGuestUser) {
+                  final connected =
+                      await context.read<SessionCubit>().linkEmailPassword(
+                            email: _emailController.text,
+                            password: _passwordController.text,
+                          );
+                  if (connected && context.mounted && context.canPop()) {
+                    context.pop();
+                  }
+                  AppSnackbar.show("Account linked successfully.");
+                } else {
+                  context.read<SessionCubit>().signInWithEmailAndPassword(
+                        email: _emailController.text,
+                        password: _passwordController.text,
+                      );
+                }
               }
             : null,
         style: FilledButton.styleFrom(
@@ -159,9 +175,9 @@ class LoginButton extends StatelessWidget {
             horizontal: 36,
           ),
         ),
-        child: const Text(
-          'Log in',
-          style: TextStyle(fontWeight: FontWeight.bold),
+        child: Text(
+          isGuestUser ? "Link" : 'Log in',
+          style: const TextStyle(fontWeight: FontWeight.bold),
         ),
       ),
     );

lib/features/session/ui/signup_page.dart

@@ -1,6 +1,8 @@
 import 'package:flutter/material.dart';
 import 'package:flutter_bloc/flutter_bloc.dart';
+import 'package:go_router/go_router.dart';
 import 'package:varanasi_mobile_app/features/session/cubit/session_cubit.dart';
+import 'package:varanasi_mobile_app/utils/app_snackbar.dart';
 import 'package:varanasi_mobile_app/utils/extensions/extensions.dart';
 import 'package:varanasi_mobile_app/widgets/input_field.dart';
 
@@ -161,18 +163,34 @@ class LoginButton extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    final authenticating = context.select((SessionCubit cubit) =>
-        cubit.state is Authenticating || cubit.state is Authenticated);
+    final isGuestUser = context.select((SessionCubit cubit) =>
+        cubit.state is Authenticated && (cubit.state as Authenticated).isGuest);
+    final authenticating = context.select((SessionCubit cubit) {
+      return cubit.state is Authenticating;
+    });
     return Align(
       alignment: Alignment.center,
       child: FilledButton.tonal(
         onPressed: isFormValid && !authenticating
-            ? () {
-                context.read<SessionCubit>().signUpWithEmailAndPassword(
-                      email: emailController.text,
-                      password: passwordController.text,
-                      name: nameController.text,
-                    );
+            ? () async {
+                if (isGuestUser) {
+                  final connected =
+                      await context.read<SessionCubit>().linkEmailPassword(
+                            email: emailController.text,
+                            password: passwordController.text,
+                            name: nameController.text,
+                          );
+                  if (connected && context.mounted && context.canPop()) {
+                    context.pop();
+                  }
+                  AppSnackbar.show("Account linked successfully.");
+                } else {
+                  context.read<SessionCubit>().signUpWithEmailAndPassword(
+                        email: emailController.text,
+                        password: passwordController.text,
+                        name: nameController.text,
+                      );
+                }
               }
             : null,
         style: FilledButton.styleFrom(
@@ -193,9 +211,9 @@ class LoginButton extends StatelessWidget {
             height: 24,
             child: CircularProgressIndicator(),
           ),
-          child: const Text(
-            'Create Account',
-            style: TextStyle(fontWeight: FontWeight.bold),
+          child: Text(
+            isGuestUser ? 'Link your account' : 'Create Account',
+            style: const TextStyle(fontWeight: FontWeight.bold),
           ),
         ),
       ),