AmendOrderAsync method in Kraken API

src/ExchangeSharp/API/Exchanges/Kraken/ExchangeKrakenAPI.cs

@@ -964,6 +964,47 @@ await GetNoncePayloadAsync(),
 			return balances;
 		}
 
+		protected override async Task<ExchangeOrderResult> OnAmendOrderAsync(
+				ExchangeOrderRequest order
+		)
+		{
+			IEnumerable<ExchangeMarket> markets = await OnGetMarketSymbolsMetadataAsync();
+			ExchangeMarket market = markets
+					.Where(m => m.MarketSymbol == order.MarketSymbol)
+					.First<ExchangeMarket>();
+
+			object nonce = await GenerateNonceAsync();
+			Dictionary<string, object> payload = new Dictionary<string, object>(
+					StringComparer.OrdinalIgnoreCase
+			)
+						{
+								{ "cl_ord_id", order.ClientOrderId },
+								{ "order_qty", order.RoundAmount().ToStringInvariant() },
+								{ "limit_price", order.Price },
+								{ "post_only", order.IsPostOnly },
+								{ "nonce", nonce }
+						};
+
+			JToken token = await MakeJsonRequestAsync<JToken>("/0/private/AmendOrder", null, payload, "POST");
+			ExchangeOrderResult result = new ExchangeOrderResult
+			{
+				OrderDate = CryptoUtility.UtcNow,
+				Result = ExchangeAPIOrderResult.Open
+			};
+			if (token["txid"] is JArray array)
+			{
+				result.OrderId = array[0].ToStringInvariant();
+			}
+			if (token["descr"] is JObject descrArray)
+			{
+				result = ExtendResultsWithOrderDescr(
+						result,
+						descrArray["order"].ToStringInvariant()
+				);
+			}
+			return result;
+		}
+
 		protected override async Task<ExchangeOrderResult> OnPlaceOrderAsync(
 				ExchangeOrderRequest order
 		)

src/ExchangeSharp/API/Exchanges/_Base/ExchangeAPI.cs

@@ -259,6 +259,10 @@ protected virtual Task<Dictionary<string, decimal>> OnGetAmountsAvailableToTrade
 				ExchangeOrderRequest order
 		) => throw new NotImplementedException();
 
+		protected virtual Task<ExchangeOrderResult> OnAmendOrderAsync(
+				ExchangeOrderRequest order
+		) => throw new NotImplementedException();
+
 		protected virtual Task<ExchangeOrderResult[]> OnPlaceOrdersAsync(
 				params ExchangeOrderRequest[] order
 		) => throw new NotImplementedException();
@@ -1307,6 +1311,13 @@ public virtual async Task<ExchangeOrderResult> PlaceOrderAsync(ExchangeOrderRequ
 			return await OnPlaceOrderAsync(order);
 		}
 
+		public virtual async Task<ExchangeOrderResult> AmendOrderAsync(ExchangeOrderRequest order)
+		{
+			await new SynchronizationContextRemover();
+			order.MarketSymbol = NormalizeMarketSymbol(order.MarketSymbol);
+			return await OnAmendOrderAsync(order);
+		}
+
 		/// <summary>
 		/// Place bulk orders
 		/// </summary>

src/ExchangeSharp/API/Exchanges/_Base/IExchangeAPI.cs

@@ -217,6 +217,13 @@ Task<Dictionary<string, decimal>> GetMarginAmountsAvailableToTradeAsync(
 		/// <returns>Order result and message string if any</returns>
 		Task<ExchangeOrderResult> PlaceOrderAsync(ExchangeOrderRequest order);
 
+		/// <summary>
+		/// Amend an order
+		/// </summary>
+		/// <param name="order">Amend request</param>
+		/// <returns>Amend result and message string if any</returns>
+		Task<ExchangeOrderResult> AmendOrderAsync(ExchangeOrderRequest order); 
+
 		/// <summary>
 		/// Place bulk orders
 		/// </summary>