first commit

services/csharp/example/Features/Auth/Login.cs

@@ -0,0 +1,42 @@
+using MediatR;
+using Microsoft.EntityFrameworkCore;
+using SequenceAuth.Example.Domain;
+using SequenceAuth.Example.Infrastructure;
+using SequenceAuth.Lib;
+
+namespace SequenceAuth.Example.Features.Auth;
+
+public record LoginCommand(string Username) : IRequest<LoginResult>;
+public record LoginResult(User User, string InitialSequence);
+
+public class LoginCommandHandler(AppDbContext dbContext, ISequenceStore sequenceStore, Microsoft.AspNetCore.Http.IHttpContextAccessor httpContextAccessor, Microsoft.Extensions.Options.IOptions<SequenceAuth.Lib.SequenceAuthOptions> options) : IRequestHandler<LoginCommand, LoginResult>
+{
+    public async Task<LoginResult> Handle(LoginCommand request, CancellationToken cancellationToken)
+    {
+        var userOpt = await dbContext.Users.FirstOrDefaultAsync(u => u.Username == request.Username, cancellationToken);
+        
+        var user = userOpt switch
+        {
+            null => await CreateUser(request.Username, cancellationToken),
+            _ => userOpt
+        };
+
+        var initialSequenceId = Guid.NewGuid().ToString("N");
+        var sequenceData = new SequenceData(UserId: user.Id.ToString(), RequestsRemaining: 1000, State: SequenceState.Initialized, NextSequenceId: initialSequenceId);
+        
+        await sequenceStore.SaveSequenceAsync(initialSequenceId, sequenceData);
+
+        httpContextAccessor.HttpContext?.Response.Headers.Append(options.Value.NextHeaderName, initialSequenceId);
+        httpContextAccessor.HttpContext?.Response.Headers.Append(options.Value.RequestsRemainingHeaderName, "1000");
+
+        return new LoginResult(user, initialSequenceId);
+    }
+
+    private async Task<User> CreateUser(string username, CancellationToken cancellationToken)
+    {
+        var user = new User(Guid.NewGuid(), username);
+        dbContext.Users.Add(user);
+        await dbContext.SaveChangesAsync(cancellationToken);
+        return user;
+    }
+}