Make Decimal json converter work for other number types

BTCPayServer.Client/JsonConverters/NumericStringJsonConverter.cs

@@ -0,0 +1,56 @@
+using System;
+using System.Globalization;
+using Newtonsoft.Json;
+using Newtonsoft.Json.Linq;
+
+namespace BTCPayServer.JsonConverters
+{
+    public class NumericStringJsonConverter : JsonConverter
+    {
+        public override bool CanConvert(Type objectType)
+        {
+            return (objectType == typeof(decimal) ||
+                    objectType == typeof(decimal?) ||
+                    objectType == typeof(double) ||
+                    objectType == typeof(double?));
+        }
+
+        public override object ReadJson(JsonReader reader, Type objectType, object existingValue,
+            JsonSerializer serializer)
+        {
+            JToken token = JToken.Load(reader);
+            switch (token.Type)
+            {
+                case JTokenType.Float:
+                case JTokenType.Integer:
+                case JTokenType.String:
+                    if (objectType == typeof(decimal) || objectType == typeof(decimal?) )
+                        return decimal.Parse(token.ToString(), CultureInfo.InvariantCulture);
+                    if (objectType == typeof(double) || objectType == typeof(double?))
+                        return double.Parse(token.ToString(), CultureInfo.InvariantCulture);
+
+                    throw new JsonSerializationException("Unexpected object type: " + objectType);
+                case JTokenType.Null when objectType == typeof(decimal?) || objectType == typeof(double?):
+                    return null;
+                default:
+                    throw new JsonSerializationException("Unexpected token type: " +
+                                                         token.Type);
+            }
+        }
+
+        public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
+        {
+            switch (value)
+            {
+                case null:
+                    break;
+                case decimal x:
+                    writer.WriteValue(x.ToString(CultureInfo.InvariantCulture));
+                    break;
+                case double x:
+                    writer.WriteValue(x.ToString(CultureInfo.InvariantCulture));
+                    break;
+            }
+        }
+    }
+}