[FA-misc] Initial MassTransit implementation seems to work

FictionArchive.Service.UserNovelDataService/Consumers/UserInvitedConsumer.cs

@@ -0,0 +1,44 @@
+using FictionArchive.Service.Shared.Contracts.Events;
+using FictionArchive.Service.UserNovelDataService.Models.Database;
+using FictionArchive.Service.UserNovelDataService.Services;
+using MassTransit;
+using Microsoft.EntityFrameworkCore;
+
+namespace FictionArchive.Service.UserNovelDataService.Consumers;
+
+public class UserInvitedConsumer : IConsumer<IUserInvited>
+{
+    private readonly ILogger<UserInvitedConsumer> _logger;
+    private readonly UserNovelDataServiceDbContext _dbContext;
+
+    public UserInvitedConsumer(
+        ILogger<UserInvitedConsumer> logger,
+        UserNovelDataServiceDbContext dbContext)
+    {
+        _logger = logger;
+        _dbContext = dbContext;
+    }
+
+    public async Task Consume(ConsumeContext<IUserInvited> context)
+    {
+        var message = context.Message;
+
+        var userId = Guid.Parse(message.InvitedUserId);
+        var exists = await _dbContext.Users.AnyAsync(u => u.Id == userId);
+        if (exists)
+        {
+            _logger.LogDebug("User {UserId} already exists, skipping", message.InvitedUserId);
+            return;
+        }
+
+        var user = new User
+        {
+            Id = userId,
+            OAuthProviderId = message.InvitedOAuthProviderId
+        };
+        _dbContext.Users.Add(user);
+        await _dbContext.SaveChangesAsync();
+
+        _logger.LogInformation("Created user stub for {UserId}", message.InvitedUserId);
+    }
+}