Merge Features.Auth and Features.UserManagement into Features.Users

web/backend/Features/Features.Users/Commands/UpdateUsername/UpdateUsernameHandler.cs

@@ -0,0 +1,36 @@
+using Domain.Exceptions;
+using Features.Auth.Dtos;
+using Features.Auth.Identity;
+using MediatR;
+using Microsoft.AspNetCore.Identity;
+
+namespace Features.Auth.Commands.UpdateUsername;
+
+/// <summary>Handles <see cref="UpdateUsernameCommand" /> via <see cref="UserManager{TUser}" />.</summary>
+public class UpdateUsernameHandler(UserManager<ApplicationUser> userManager)
+    : IRequestHandler<UpdateUsernameCommand, UpdateUsernamePayload>
+{
+    /// <exception cref="NotFoundException">Thrown when the account does not exist.</exception>
+    /// <exception cref="ConflictException">Thrown when the requested username is already taken.</exception>
+    public async Task<UpdateUsernamePayload> Handle(
+        UpdateUsernameCommand request,
+        CancellationToken cancellationToken
+    )
+    {
+        ApplicationUser user =
+            await userManager.FindByIdAsync(request.UserAccountId.ToString())
+            ?? throw new NotFoundException("User account not found");
+
+        IdentityResult result = await userManager.SetUserNameAsync(user, request.NewUsername);
+        if (!result.Succeeded)
+        {
+            if (result.Errors.Any(e => e.Code == "DuplicateUserName"))
+                throw new ConflictException("Username already exists");
+            throw new ConflictException(
+                string.Join("; ", result.Errors.Select(e => e.Description))
+            );
+        }
+
+        return new UpdateUsernamePayload(user.Id, user.UserName);
+    }
+}