Support specifying payment method through apps (#1539)

* Support specifying payment method through apps

closes #1525
This is great if you want to offer items with an incentive to use a specific payment method without messing with the rates.
For example, you can have `Item A` which costs 25$ and your store is configured for USDT and BTC. You can create two items, with different prices, where Item A costs 20$ if you pay with bitcoin or 25$ if you paid in dirty fiat pegs

* make code cleaner

* Add Test

* fix test

* fix test

BTCPayServer.Tests/UnitTest1.cs

@@ -2265,14 +2265,17 @@ namespace BTCPayServer.Tests
 
         [Fact]
         [Trait("Integration", "Integration")]
+        [Trait("Altcoins", "Altcoins")]
         public async Task CanUsePoSApp()
         {
             using (var tester = ServerTester.Create())
             {
+                tester.ActivateLTC();
                 await tester.StartAsync();
                 var user = tester.NewAccount();
                 user.GrantAccess();
                 user.RegisterDerivationScheme("BTC");
+                user.RegisterDerivationScheme("LTC");
                 var apps = user.GetController<AppsController>();
                 var vm = Assert.IsType<CreateAppViewModel>(Assert.IsType<ViewResult>(apps.CreateApp().Result).Model);
                 vm.Name = "test";
@@ -2443,6 +2446,41 @@ noninventoryitem:
                     Assert.Equal(1,
                         appService.Parse(vmpos.Template, "BTC").Single(item => item.Id == "inventoryitem").Inventory);
                 }, 10000);
+
+
+                //test payment methods option
+                
+                vmpos = Assert.IsType<UpdatePointOfSaleViewModel>(Assert
+                    .IsType<ViewResult>(apps.UpdatePointOfSale(appId).Result).Model);
+                vmpos.Title = "hello";
+                vmpos.Currency = "BTC";
+                vmpos.Template = @"
+btconly:
+  price: 1.0
+  title: good apple
+  payment_methods:
+    - BTC
+normal:
+  price: 1.0";
+                Assert.IsType<RedirectToActionResult>(apps.UpdatePointOfSale(appId, vmpos).Result);
+                Assert.IsType<RedirectToActionResult>(publicApps
+                    .ViewPointOfSale(appId, 1, null, null, null, null, "btconly").Result);
+                Assert.IsType<RedirectToActionResult>(publicApps
+                    .ViewPointOfSale(appId, 1, null, null, null, null, "normal").Result);
+                invoices = user.BitPay.GetInvoices();
+                var normalInvoice = invoices.Single(invoice => invoice.ItemCode == "normal");
+                var btcOnlyInvoice = invoices.Single(invoice => invoice.ItemCode == "btconly");
+                Assert.Single(btcOnlyInvoice.CryptoInfo);
+                Assert.Equal("BTC",
+                    btcOnlyInvoice.CryptoInfo.First().CryptoCode);
+                Assert.Equal(PaymentTypes.BTCLike.ToString(),
+                    btcOnlyInvoice.CryptoInfo.First().PaymentType);
+
+                Assert.Equal(2, normalInvoice.CryptoInfo.Length);
+                Assert.Contains(
+                    normalInvoice.CryptoInfo,
+                    s => PaymentTypes.BTCLike.ToString() == s.PaymentType &&  new[] {"BTC", "LTC"}.Contains(
+                             s.CryptoCode));
             }
         }
 

BTCPayServer/Controllers/AppsPublicController.cs

@@ -17,6 +17,7 @@ using Microsoft.AspNetCore.Cors;
 using Microsoft.AspNetCore.Http.Extensions;
 using Microsoft.AspNetCore.Identity;
 using Microsoft.AspNetCore.Mvc;
+using NBitpayClient;
 using static BTCPayServer.Controllers.AppsController;
 
 namespace BTCPayServer.Controllers
@@ -111,6 +112,7 @@ namespace BTCPayServer.Controllers
             }
             string title = null;
             var price = 0.0m;
+            Dictionary<string, InvoiceSupportedTransactionCurrency> paymentMethods = null;
             ViewPointOfSaleViewModel.Item choice = null;
             if (!string.IsNullOrEmpty(choiceKey))
             {
@@ -130,6 +132,12 @@ namespace BTCPayServer.Controllers
                         return RedirectToAction(nameof(ViewPointOfSale), new { appId = appId });
                     }
                 }
+
+                if (choice?.PaymentMethods?.Any() is true)
+                {
+                    paymentMethods = choice?.PaymentMethods.ToDictionary(s => s,
+                        s => new InvoiceSupportedTransactionCurrency() {Enabled = true});
+                }
             }
             else
             {
@@ -182,6 +190,7 @@ namespace BTCPayServer.Controllers
                     ExtendedNotifications = true,
                     PosData = string.IsNullOrEmpty(posData) ? null : posData,
                     RedirectAutomatically = settings.RedirectAutomatically,
+                    SupportedTransactionCurrencies = paymentMethods,
                 }, store, HttpContext.Request.GetAbsoluteRoot(),
                     new List<string>() { AppService.GetAppInternalTag(appId) },
                     cancellationToken);
@@ -270,6 +279,7 @@ namespace BTCPayServer.Controllers
             var store = await _AppService.GetStore(app);
             var title = settings.Title;
             var price = request.Amount;
+            Dictionary<string, InvoiceSupportedTransactionCurrency> paymentMethods = null;
             ViewPointOfSaleViewModel.Item choice = null;
             if (!string.IsNullOrEmpty(request.ChoiceKey))
             {
@@ -290,6 +300,13 @@ namespace BTCPayServer.Controllers
                         return NotFound("Option was out of stock");
                     }
                 }
+                
+
+                if (choice?.PaymentMethods?.Any() is true)
+                {
+                    paymentMethods = choice?.PaymentMethods.ToDictionary(s => s,
+                        s => new InvoiceSupportedTransactionCurrency() {Enabled = true});
+                }
             }
 
             if (!isAdmin && (settings.EnforceTargetAmount && info.TargetAmount.HasValue && price >
@@ -311,6 +328,7 @@ namespace BTCPayServer.Controllers
                         NotificationURL = settings.NotificationUrl,
                         FullNotifications = true,
                         ExtendedNotifications = true,
+                        SupportedTransactionCurrencies = paymentMethods,
                         RedirectURL = request.RedirectUrl ?? 
                                      new Uri(new Uri( new Uri(HttpContext.Request.GetAbsoluteRoot()),  _BtcPayServerOptions.RootPath), $"apps/{appId}/crowdfund").ToString()
                     }, store, HttpContext.Request.GetAbsoluteRoot(),

BTCPayServer/Models/AppViewModels/ViewPointOfSaleViewModel.cs

@@ -21,6 +21,7 @@ namespace BTCPayServer.Models.AppViewModels
             public string Title { get; set; }
             public bool Custom { get; set; }
             public int? Inventory { get; set; } = null;
+            public string[] PaymentMethods { get; set; }
         }
 
         public class CurrencyInfoData

BTCPayServer/Services/Apps/AppService.cs

@@ -333,7 +333,9 @@ namespace BTCPayServer.Services.Apps
                                  Formatted = Currencies.FormatCurrency(cc.Value.Value, currency)
                              }).Single(),
                     Custom = c.GetDetailString("custom") == "true",
-                    Inventory = string.IsNullOrEmpty(c.GetDetailString("inventory")) ?(int?) null:  int.Parse(c.GetDetailString("inventory"), CultureInfo.InvariantCulture)
+                    Inventory = string.IsNullOrEmpty(c.GetDetailString("inventory")) ?(int?) null:  int.Parse(c.GetDetailString("inventory"), CultureInfo.InvariantCulture),
+                    PaymentMethods = c.GetDetailStringList("payment_methods")
+                    
                 })
                 .ToArray();
         }
@@ -411,6 +413,14 @@ namespace BTCPayServer.Services.Apps
             {
                 return GetDetail(field).FirstOrDefault()?.Value?.Value;
             }
+            public string[] GetDetailStringList(string field)
+            {
+                if (!Value.Children.ContainsKey(field) || !( Value.Children[field] is YamlSequenceNode sequenceNode))
+                {
+                    return null;
+                }
+                return sequenceNode.Children.Select(node => (node as YamlScalarNode)?.Value).Where( s => s!= null).ToArray();
+            }
         }
         private class PosScalar
         {