Estimate rate with BTCPay if BitcoinAverage stops works

BTCPayServer/BTCPayServer.csproj

@@ -2,7 +2,7 @@
   <PropertyGroup>
     <OutputType>Exe</OutputType>
     <TargetFramework>netcoreapp2.0</TargetFramework>
-		<Version>1.0.0.38</Version>
+		<Version>1.0.0.39</Version>
   </PropertyGroup>
   <ItemGroup>
     <Compile Remove="Build\dockerfiles\**" />

BTCPayServer/Hosting/BTCPayServerServices.cs

@@ -141,7 +141,9 @@ namespace BTCPayServer.Hosting
             });
             services.TryAddSingleton<IRateProvider>(o =>
             {
-                return new CachedRateProvider(new CoinAverageRateProvider(), o.GetRequiredService<IMemoryCache>()) { CacheSpan = TimeSpan.FromMinutes(1.0) };
+                var coinaverage = new CoinAverageRateProvider();
+                var bitpay = new BitpayRateProvider(new Bitpay(new Key(), new Uri("https://bitpay.com/")));
+                return new CachedRateProvider(new FallbackRateProvider(new IRateProvider[] { coinaverage, bitpay }), o.GetRequiredService<IMemoryCache>()) { CacheSpan = TimeSpan.FromMinutes(1.0) };
             });
             services.TryAddSingleton<InvoiceWatcher>();
             services.TryAddSingleton<InvoiceNotificationManager>();

BTCPayServer/Services/Rates/FallbackRateProvider.cs

@@ -0,0 +1,43 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+
+namespace BTCPayServer.Services.Rates
+{
+    public class FallbackRateProvider : IRateProvider
+    {
+        IRateProvider[] _Providers;
+        public FallbackRateProvider(IRateProvider[] providers)
+        {
+            if (providers == null)
+                throw new ArgumentNullException(nameof(providers));
+            _Providers = providers;
+        }
+        public async Task<decimal> GetRateAsync(string currency)
+        {
+            foreach(var p in _Providers)
+            {
+                try
+                {
+                    return await p.GetRateAsync(currency).ConfigureAwait(false);
+                }
+                catch { }
+            }
+            throw new RateUnavailableException(currency);
+        }
+
+        public async Task<ICollection<Rate>> GetRatesAsync()
+        {
+            foreach (var p in _Providers)
+            {
+                try
+                {
+                    return await p.GetRatesAsync().ConfigureAwait(false);
+                }
+                catch { }
+            }
+            throw new RateUnavailableException("ALL");
+        }
+    }
+}