Add =КУРСЕВРО() function

RhSolutions.AddIn/AddIn/RhSolutionsFunction.cs

@@ -185,4 +185,34 @@ public class RhSolutionsFunction
             }
         }
     }
+
+    [ExcelFunction(Description = "Получить курс евро по ЦБ")]
+    public static object КУРСЕВРО([ExcelArgument(Name = "ДАТА", Description = "Дата в формате Excel (необязательно)")] double dateField)
+    {
+        ICurrencyClient currencyClient = RhSolutionsAddIn.ServiceProvider.GetRequiredService<ICurrencyClient>();
+
+        if (ExcelAsyncUtil.Run("Database request", dateField, delegate
+        {
+            DateTime date = dateField == 0 ? DateTime.Now : DateTime.FromOADate(dateField);
+            var exchangeRate = currencyClient.GetCurrencyCourse(date)
+                .GetAwaiter()
+                .GetResult();
+
+            return exchangeRate ?? -1m;
+        }) is not decimal requestResult)
+        {
+            return "Загрузка...";
+        }
+        else
+        {
+            if (requestResult < 0)
+            {
+                return ExcelError.ExcelErrorNA;
+            }
+            else
+            {
+                return Math.Round(requestResult, 2);
+            }
+        }
+    }
 }