[feature/backend] update put /users/me endpoint, allow setting username and display name

backend/internal/service/user.go

@@ -40,6 +40,25 @@ func (s *serviceImpl) UpdateUser(ctx context.Context, userID int, input *types.U
 	// Start building the update
 	update := s.client.User.UpdateOneID(userID)
 
+	// Update username if provided
+	if input.Username != "" {
+		// Check if username is already taken
+		exists, err := s.client.User.Query().
+			Where(user.And(
+				user.UsernameEQ(input.Username),
+				user.IDNEQ(userID),
+			)).
+			Exist(ctx)
+		if err != nil {
+			log.Error().Err(err).Msg("Failed to check username availability")
+			return nil, fmt.Errorf("failed to check username availability: %w", err)
+		}
+		if exists {
+			return nil, fmt.Errorf("username already taken")
+		}
+		update.SetUsername(input.Username)
+	}
+
 	// Update email if provided
 	if input.Email != "" {
 		update.SetEmail(input.Email)