[FA-27] Need to test events but seems to mostly work

FictionArchive.Service.UserNovelDataService/Services/EventHandlers/UserInvitedEventHandler.cs

@@ -0,0 +1,40 @@
+using FictionArchive.Service.Shared.Services.EventBus;
+using FictionArchive.Service.UserNovelDataService.Models.Database;
+using FictionArchive.Service.UserNovelDataService.Models.IntegrationEvents;
+using Microsoft.EntityFrameworkCore;
+
+namespace FictionArchive.Service.UserNovelDataService.Services.EventHandlers;
+
+public class UserInvitedEventHandler : IIntegrationEventHandler<UserInvitedEvent>
+{
+    private readonly UserNovelDataServiceDbContext _dbContext;
+    private readonly ILogger<UserInvitedEventHandler> _logger;
+
+    public UserInvitedEventHandler(
+        UserNovelDataServiceDbContext dbContext,
+        ILogger<UserInvitedEventHandler> logger)
+    {
+        _dbContext = dbContext;
+        _logger = logger;
+    }
+
+    public async Task Handle(UserInvitedEvent @event)
+    {
+        var exists = await _dbContext.Users.AnyAsync(u => u.Id == @event.InvitedUserId);
+        if (exists)
+        {
+            _logger.LogDebug("User {UserId} already exists, skipping", @event.InvitedUserId);
+            return;
+        }
+
+        var user = new User
+        {
+            Id = @event.InvitedUserId,
+            OAuthProviderId = @event.InvitedOAuthProviderId
+        };
+        _dbContext.Users.Add(user);
+        await _dbContext.SaveChangesAsync();
+
+        _logger.LogInformation("Created user stub for {UserId}", @event.InvitedUserId);
+    }
+}