Properly deserialize source on BT during expand

src/Stripe.Tests.XUnit/charges/when_creating_charges_with_multiple_expand.cs

@@ -25,7 +25,7 @@ public when_creating_charges_with_multiple_expand()
                 Currency = "usd",
                 Destination = account.Id,
             };
-            chargeOptions.AddExpand("balance_transaction");
+            chargeOptions.AddExpand("balance_transaction.source");
             chargeOptions.AddExpand("transfer.balance_transaction.source");
             chargeOptions.AddExpand("destination");
 
@@ -34,13 +34,19 @@ public when_creating_charges_with_multiple_expand()
             accountService.Delete(account.Id);
         }
 
-
         [Fact]
         public void should_have_all_objects_expanded()
         {
             Charge.BalanceTransactionId.Should().Be(Charge.BalanceTransaction.Id);
             Charge.DestinationId.Should().Be(Charge.Destination.Id);
             Charge.Transfer.BalanceTransaction.Source.Id.Should().Be(Charge.Transfer.Id);
         }
+
+        [Fact]
+        public void should_properly_deserialize_balance_transaction_source()
+        {
+            Charge.BalanceTransaction.Source.Type.Should().Be(BalanceTransactionSourceType.Charge);
+            Charge.BalanceTransaction.SourceId.Should().Be(Charge.BalanceTransaction.Source.Charge.Id);
+        }
     }
 }

src/Stripe.net/Entities/BalanceTransactionSource.cs

@@ -0,0 +1,25 @@
+using Newtonsoft.Json;
+using Stripe.Infrastructure;
+
+namespace Stripe
+{
+    public enum BalanceTransactionSourceType
+    {
+        Charge,
+        Payout,
+        Refund,
+        Transfer,
+        Unknown,
+    }
+
+    [JsonConverter(typeof(BalanceTransactionSourceConverter))]
+    public class BalanceTransactionSource : StripeEntityWithId
+    {
+        public BalanceTransactionSourceType Type { get; set; }
+
+        public StripeCharge Charge { get; set; }
+        public StripePayout Payout { get; set; }
+        public StripeRefund Refund { get; set; }
+        public StripeTransfer Transfer { get; set; }
+    }
+}

src/Stripe.net/Entities/StripeBalanceTransaction.cs

@@ -36,18 +36,18 @@ public class StripeBalanceTransaction : StripeEntityWithId
         [JsonProperty("net")]
         public int Net { get; set; }
 
-        #region Expandable Source
+        #region Expandable BalanceTransactionSource
         public string SourceId { get; set; }
 
         [JsonIgnore]
-        public StripeSource Source { get; set; }
+        public BalanceTransactionSource Source { get; set; }
 
         [JsonProperty("source")]
         internal object InternalSource
         {
             set
             {
-                StringOrObject<StripeSource>.Map(value, s => SourceId = s, o => Source = o);
+                StringOrObject<BalanceTransactionSource>.Map(value, s => SourceId = s, o => Source = o);
             }
         }
         #endregion

src/Stripe.net/Infrastructure/JsonConverters/BalanceTransactionSourceConverter.cs

@@ -0,0 +1,60 @@
+using System;
+using Newtonsoft.Json;
+using Newtonsoft.Json.Linq;
+
+namespace Stripe.Infrastructure
+{
+    internal class BalanceTransactionSourceConverter : JsonConverter
+    {
+        public override bool CanWrite => false;
+
+        public override bool CanConvert(Type objectType)
+        {
+            throw new NotImplementedException();
+        }
+
+        public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
+        {
+            var incoming = JObject.FromObject(value);
+
+            incoming.WriteTo(writer);
+        }
+
+        public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
+        {
+            var incoming = JObject.Load(reader);
+
+            var source = new BalanceTransactionSource
+            {
+                Id = incoming.SelectToken("id").ToString()
+            };
+
+            if (incoming.SelectToken("object")?.ToString() == "charge")
+            {
+                source.Type = BalanceTransactionSourceType.Charge;
+                source.Charge = Mapper<StripeCharge>.MapFromJson(incoming.ToString());
+            }
+            else if (incoming.SelectToken("object")?.ToString() == "payout")
+            {
+                source.Type = BalanceTransactionSourceType.Payout;
+                source.Payout = Mapper<StripePayout>.MapFromJson(incoming.ToString());
+            }
+            else if (incoming.SelectToken("object")?.ToString() == "refund")
+            {
+                source.Type = BalanceTransactionSourceType.Refund;
+                source.Refund = Mapper<StripeRefund>.MapFromJson(incoming.ToString());
+            }
+            else if (incoming.SelectToken("object")?.ToString() == "transfer")
+            {
+                source.Type = BalanceTransactionSourceType.Transfer;
+                source.Transfer = Mapper<StripeTransfer>.MapFromJson(incoming.ToString());
+            }
+            else
+            {
+                source.Type = BalanceTransactionSourceType.Unknown;
+            }
+
+            return source;
+        }
+    }
+}