fix issue with changelly rates and cover with UTs (#368)

BTCPayServer.Tests/ChangellyTests.cs

@@ -118,7 +118,7 @@ namespace BTCPayServer.Tests
                 var changellyController =
                     tester.PayTester.GetController<ChangellyController>(user.UserId, user.StoreId);
                 changellyController.IsTest = true;
-                
+
                 //test non existing payment method
                 Assert.IsType<BitpayErrorModel>(Assert
                     .IsType<BadRequestObjectResult>(await changellyController.GetCurrencyList(user.StoreId))
@@ -143,7 +143,6 @@ namespace BTCPayServer.Tests
                 Assert.Equal("UpdateStore", Assert.IsType<RedirectToActionResult>(
                     await storesController.UpdateChangellySettings(user.StoreId, updateModel, "save")).ActionName);
 
-                
 
                 Assert.IsNotType<BitpayErrorModel>(Assert
                     .IsType<OkObjectResult>(await changellyController.GetCurrencyList(user.StoreId))
@@ -179,18 +178,18 @@ namespace BTCPayServer.Tests
                 //confirm saved
                 Assert.Equal("UpdateStore", Assert.IsType<RedirectToActionResult>(
                     await storesController.UpdateChangellySettings(user.StoreId, updateModel, "save")).ActionName);
-                
+
                 var factory = UnitTest1.CreateBTCPayRateFactory();
                 var fetcher = new RateFetcher(factory);
                 var httpClientFactory = new MockHttpClientFactory();
                 var changellyController = new ChangellyController(
-                    new ChangellyClientProvider(tester.PayTester.StoreRepository,httpClientFactory), tester.NetworkProvider, fetcher);
+                    new ChangellyClientProvider(tester.PayTester.StoreRepository, httpClientFactory),
+                    tester.NetworkProvider, fetcher);
                 changellyController.IsTest = true;
                 var result = Assert
                     .IsType<OkObjectResult>(await changellyController.GetCurrencyList(user.StoreId))
                     .Value as IEnumerable<CurrencyFull>;
                 Assert.True(result.Any());
-
             }
         }
 
@@ -215,20 +214,40 @@ namespace BTCPayServer.Tests
                 var fetcher = new RateFetcher(factory);
                 var httpClientFactory = new MockHttpClientFactory();
                 var changellyController = new ChangellyController(
-                    new ChangellyClientProvider(tester.PayTester.StoreRepository,httpClientFactory), tester.NetworkProvider, fetcher);
+                    new ChangellyClientProvider(tester.PayTester.StoreRepository, httpClientFactory),
+                    tester.NetworkProvider, fetcher);
                 changellyController.IsTest = true;
                 Assert.IsType<decimal>(Assert
-                    .IsType<OkObjectResult>(await changellyController.CalculateAmount(user.StoreId, "ltc", "btc", 1.0m)).Value);
+                    .IsType<OkObjectResult>(await changellyController.CalculateAmount(user.StoreId, "ltc", "btc", 1.0m))
-
+                    .Value);
             }
         }
+
+        [Fact]
+        [Trait("Integration", "Integration")]
+        public void CanComputeBaseAmount()
+        {
+            Assert.Equal(1, ChangellyCalculationHelper.ComputeBaseAmount(1, 1));
+            Assert.Equal(0.5m, ChangellyCalculationHelper.ComputeBaseAmount(1, 0.5m));
+            Assert.Equal(2, ChangellyCalculationHelper.ComputeBaseAmount(0.5m, 1));
+            Assert.Equal(4m, ChangellyCalculationHelper.ComputeBaseAmount(1, 4));
+        }
+
+        [Fact]
+        [Trait("Integration", "Integration")]
+        public void CanComputeCorrectAmount()
+        {
+            Assert.Equal(1, ChangellyCalculationHelper.ComputeCorrectAmount(0.5m, 1, 2));
+            Assert.Equal(0.25m, ChangellyCalculationHelper.ComputeCorrectAmount(0.5m, 1, 0.5m));
+            Assert.Equal(20, ChangellyCalculationHelper.ComputeCorrectAmount(10, 1, 2));
+        }
     }
 
     public class MockHttpClientFactory : IHttpClientFactory
     {
         public HttpClient CreateClient(string name)
         {
-            return  new HttpClient();
+            return new HttpClient();
         }
     }
 }

BTCPayServer/Controllers/ChangellyController.cs

@@ -61,8 +61,8 @@ namespace BTCPayServer.Controllers
                 }
                 
                 var callCounter = 0;
-                var response1 = await client.GetExchangeAmount(fromCurrency, toCurrency, 1);
+                var baseRate = await client.GetExchangeAmount(fromCurrency, toCurrency, 1);
-                var currentAmount = response1;
+                var currentAmount = ChangellyCalculationHelper.ComputeBaseAmount(baseRate, toCurrencyAmount);
                 while (true)
                 {
                     if (callCounter > 10)
@@ -70,13 +70,13 @@ namespace BTCPayServer.Controllers
                         BadRequest();
                     }
 
-                    var response2 = await client.GetExchangeAmount(fromCurrency, toCurrency, currentAmount);
+                    var computedAmount = await client.GetExchangeAmount(fromCurrency, toCurrency, currentAmount);
                     callCounter++;
-                    if (response2 < toCurrencyAmount)
+                    if (computedAmount < toCurrencyAmount)
                     {
-                        var newCurrentAmount = ((toCurrencyAmount / response2) * 1m) * currentAmount;
+                        currentAmount =
-
+                            ChangellyCalculationHelper.ComputeCorrectAmount(currentAmount, computedAmount,
-                        currentAmount = newCurrentAmount;
+                                toCurrencyAmount);
                     }
                     else
                     {
@@ -114,4 +114,6 @@ namespace BTCPayServer.Controllers
 
         public bool IsTest { get; set; } = false;
     }
+    
+    
 }

BTCPayServer/Payments/Changelly/ChangellyCalculationHelper.cs

@@ -0,0 +1,16 @@
+namespace BTCPayServer.Payments.Changelly
+{
+    public static class ChangellyCalculationHelper
+    {
+        public static decimal ComputeBaseAmount(decimal baseRate, decimal toAmount)
+        {
+            return (1m / baseRate) * toAmount;
+        }
+
+        public static decimal ComputeCorrectAmount(decimal currentFromAmount, decimal currentAmount,
+            decimal expectedAmount)
+        {
+            return (currentFromAmount / currentAmount) * expectedAmount;
+        }
+    }
+}