An invoicing app (C#)

C# on Windows: customers and invoices, with approvals.

A Windows desktop app in C# (.NET 8) that lists customers and makes sales invoices as the person signed in, with their branch, territory and approval rules.

1. RegisterKind Mobile or desktop, callback http://127.0.0.1:53682/callback (a port your app listens on), permissions invoice.read invoice.write.
2. Sign in through the browser
   CSHARP

   Copy

   // dotnet add package IdentityModel.OidcClient
   var options = new OidcClientOptions {
       Authority = "https://accounts.zilomail.in/oidc",
       ClientId = "zo_app_…",
       Scope = "openid email profile invoice.read invoice.write",
       RedirectUri = "http://127.0.0.1:53682/callback",
       Browser = new SystemBrowser(53682),              // opens the default browser, listens for the callback
   };
   var oidc = new OidcClient(options);
   var login = await oidc.LoginAsync();                 // PKCE and state included
   if (login.IsError) throw new Exception(login.Error);
   tokens.Save(login.AccessToken, login.RefreshToken);  // ProtectedData (DPAPI)

3. List customers
   CSHARP

   Copy

   var http = new HttpClient(new RefreshTokenDelegatingHandler(oidc, tokens.Access, tokens.Refresh)) { BaseAddress = new Uri("https://api.zilomail.in/") };
   var page = await http.GetFromJsonAsync<Page<Customer>>("v1/invoice/customers?limit=100&q=kumar");
   foreach (var c in page!.Data) Console.WriteLine($"{c.Code}  {c.Name}  owes {c.Outstanding}");
   
   record Page<T>(List<T> Data, string? Next);
   record Customer(string Id, string Code, string Name, string Outstanding);

4. Make an invoice, and handle approval
   CSHARP

   Copy

   var req = new HttpRequestMessage(HttpMethod.Post, "v1/invoice/invoices") {
       Content = JsonContent.Create(new {
           customerId = customer.Id,
           date = DateTime.Today.ToString("yyyy-MM-dd"),
           lines = new[] { new { productId = tea.Id, quantity = 12 } },
       }),
   };
   req.Headers.Add("Idempotency-Key", Guid.NewGuid().ToString());   // safe to retry
   var res = await http.SendAsync(req);
   
   if (res.StatusCode == HttpStatusCode.Accepted) {
       var waiting = await res.Content.ReadFromJsonAsync<Pending>();
       ShowBanner($"Sent for approval ({waiting!.Approval.Id})");    // check later: GET v1/approvals/{id}
   } else {
       res.EnsureSuccessStatusCode();
       var invoice = await res.Content.ReadFromJsonAsync<Invoice>();
       ShowBanner($"Invoice {invoice!.Number}: {invoice.Total}");
   }