Added a custom NextFundingRateConverter that adds the offset to the c…

…urrent time instead (#212)

Kucoin.Net/Converters/NextFundingRateTimeConverter.cs

@@ -0,0 +1,41 @@
+using System;
+using Newtonsoft.Json;
+
+namespace Kucoin.Net.Converters
+{
+    /// <summary>
+    /// Does basically the same thing as the shared DateTimeConverter, with a slight difference.
+    /// Instead of adding the time to Jan 01 1970, it adds it to the current time. This isn't ideal since
+    /// it produces inaccuracies, but it's the format the kucoin api returns for the next funding rate time.
+    /// </summary>
+    internal class NextFundingRateTimeConverter : JsonConverter<DateTime?>
+    {
+        public override DateTime? ReadJson(
+            JsonReader reader,
+            Type objectType,
+            DateTime? existingValue,
+            bool hasExistingValue,
+            JsonSerializer serializer
+        )
+        {
+            if (reader.Value == null)
+            {
+                return null;
+            }
+
+            var value = (long)reader.Value;
+            var now = DateTime.UtcNow;
+            var offset = TimeSpan.FromMilliseconds(value);
+            return now + offset;
+        }
+
+        public override void WriteJson(
+            JsonWriter writer,
+            DateTime? value,
+            JsonSerializer serializer
+        )
+        {
+            throw new NotSupportedException("This converter only supports reading");
+        }
+    }
+}

Kucoin.Net/Objects/Models/Futures/KucoinContract.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using CryptoExchange.Net.Converters;
+using Kucoin.Net.Converters;
 using Newtonsoft.Json;
 
 namespace Kucoin.Net.Objects.Models.Futures
@@ -206,9 +207,11 @@ public class KucoinContract
         /// </summary>
         public decimal? PredictedFundingFeeRate { get; set; }
         /// <summary>
-        /// Next funding rate time
+        /// Next funding rate time. This time may not be accurate up to a couple of seconds.
+        /// This is due to the fact that the API returns this value as an offset from the current time, 
+        /// but we have no way of knowing the exact time the API returned this value.
         /// </summary>
-        [JsonConverter(typeof(DateTimeConverter))]
+        [JsonConverter(typeof(NextFundingRateTimeConverter))]
         public DateTime? NextFundingRateTime { get; set; }
         /// <summary>
         /// Source exchanges
@@ -243,4 +246,4 @@ public class KucoinContract
         /// </summary>
         public string? FundingQuoteSymbol1M { get; set; }
     }
-}
+}