chore: moved ChallengeNameType.mfaSetup switch statement logic to a helper method

Author: khatruong2009

packages/auth/amplify_auth_cognito_dart/lib/src/state/machines/sign_in_state_machine.dart

@@ -330,55 +330,8 @@ final class SignInStateMachine
         createEmailMfaRequest(event),
       ChallengeNameType.selectMfaType when hasUserResponse =>
         createSelectMfaRequest(event),
-      ChallengeNameType.mfaSetup => (() async {
-          final allowedMfaTypes = _allowedMfaTypes;
-          if (allowedMfaTypes == null || allowedMfaTypes.isEmpty) {
-            throw const InvalidUserPoolConfigurationException(
-              'No MFA types are allowed for setup.',
-              recoverySuggestion: 'Check your user pool MFA configuration.',
-            );
-          }
-          // Exclude MfaType.sms from consideration
-          final mfaTypesForSetup = allowedMfaTypes.difference({MfaType.sms});
-          if (mfaTypesForSetup.isEmpty) {
-            throw const InvalidUserPoolConfigurationException(
-              'No eligible MFA types are available for setup.',
-              recoverySuggestion: 'Check your user pool MFA configuration.',
-            );
-          }
-          if (mfaTypesForSetup.length == 1) {
-            final mfaType = mfaTypesForSetup.first;
-            if (mfaType == MfaType.totp) {
-              _enableMfaType = MfaType.totp;
-              _totpSetupResult ??= await associateSoftwareToken();
-              if (hasUserResponse) {
-                return createMfaSetupRequest(event);
-              } else {
-                // Need to prompt user for the TOTP code
-                return null;
-              }
-            } else if (mfaType == MfaType.email) {
-              _enableMfaType = MfaType.email;
-              if (hasUserResponse) {
-                return createEmailMfaSetupRequest(event);
-              } else {
-                // Need to prompt user for the email verification code
-                return null;
-              }
-            } else {
-              throw InvalidUserPoolConfigurationException(
-                'Unsupported MFA type: ${mfaType.name}',
-                recoverySuggestion: 'Check your user pool MFA configuration.',
-              );
-            }
-          } else if (hasUserResponse) {
-            // Handle user's selection
-            return createMfaSetupRequest(event);
-          } else {
-            // Need to prompt user to select an MFA type
-            return null;
-          }
-        })(),
+      ChallengeNameType.mfaSetup =>
+        handleMfaSetup(event: event, hasUserResponse: hasUserResponse),
       ChallengeNameType.newPasswordRequired when hasUserResponse =>
         createNewPasswordRequest(event),
       _ => null,
@@ -698,6 +651,63 @@ final class SignInStateMachine
     }
   }
 
+  /// Handles the MFA setup challenge.
+  @protected
+  Future<RespondToAuthChallengeRequest?> handleMfaSetup({
+    SignInEvent? event,
+    required bool hasUserResponse,
+  }) async {
+    final allowedMfaTypes = _allowedMfaTypes;
+    if (allowedMfaTypes == null || allowedMfaTypes.isEmpty) {
+      throw const InvalidUserPoolConfigurationException(
+        'No MFA types are allowed for setup.',
+        recoverySuggestion: 'Check your user pool MFA configuration.',
+      );
+    }
+
+    // Exclude MfaType.sms from consideration
+    final mfaTypesForSetup = allowedMfaTypes.difference({MfaType.sms});
+    if (mfaTypesForSetup.isEmpty) {
+      throw const InvalidUserPoolConfigurationException(
+        'No eligible MFA types are available for setup.',
+        recoverySuggestion: 'Check your user pool MFA configuration.',
+      );
+    }
+
+    if (mfaTypesForSetup.length == 1) {
+      final mfaType = mfaTypesForSetup.first;
+      if (mfaType == MfaType.totp) {
+        _enableMfaType = MfaType.totp;
+        _totpSetupResult ??= await associateSoftwareToken();
+        if (hasUserResponse) {
+          return createMfaSetupRequest(event as SignInRespondToChallenge);
+        } else {
+          // Need to prompt user for the TOTP code
+          return null;
+        }
+      } else if (mfaType == MfaType.email) {
+        _enableMfaType = MfaType.email;
+        if (hasUserResponse) {
+          return createEmailMfaSetupRequest(event as SignInRespondToChallenge);
+        } else {
+          // Need to prompt user for the email verification code
+          return null;
+        }
+      } else {
+        throw InvalidUserPoolConfigurationException(
+          'Unsupported MFA type: ${mfaType.name}',
+          recoverySuggestion: 'Check your user pool MFA configuration.',
+        );
+      }
+    } else if (hasUserResponse) {
+      // Handle user's selection
+      return createMfaSetupRequest(event as SignInRespondToChallenge);
+    } else {
+      // Need to prompt user to select an MFA type
+      return null;
+    }
+  }
+
   /// Completes set up of a TOTP MFA.
   @protected
   Future<RespondToAuthChallengeRequest> createMfaSetupRequest(