Fix #1407: Add distance type to geo distance sort

Author: gmarz

src/Nest/DSL/Search/SortGeoDistanceDescriptor.cs

@@ -15,22 +15,25 @@ public interface IGeoDistanceSort : ISort, ICustomJson
 		string PinLocation { get; set; }
 		IEnumerable<string> Points { get; set; }
 		GeoUnit? GeoUnit { get; set; }
+		GeoDistance? DistanceType { get; set; }
 	}
 
 	public class GeoDistanceSort : SortBase, IGeoDistanceSort
 	{
-		internal static List<string> Params = new List<string> { "missing", "mode", "order", "unit" };
+		internal static List<string> Params = new List<string> { "missing", "mode", "order", "unit", "distance_type" };
 
 		internal static int MissingIndex = 0;
 		internal static int ModeIndex = 1;
 		internal static int OrderIndex = 2;
 		internal static int UnitIndex = 3;
+		internal static int DistanceTypeIndex = 4;
 
 		public PropertyPathMarker Field { get; set; }
 		public string PinLocation { get; set; }
 		public IEnumerable<string> Points { get; set; }
 		public GeoUnit? GeoUnit { get; set; }
-		
+		public GeoDistance? DistanceType { get; set; }
+
 		object ICustomJson.GetCustomJson()
 		{
 			var sort = this.Points.HasAny() ? (object)this.Points : this.PinLocation;
@@ -40,7 +43,8 @@ object ICustomJson.GetCustomJson()
 				{ Params[MissingIndex], this.Missing },
 				{ Params[ModeIndex], this.Mode},
 				{ Params[OrderIndex], this.Order },
-				{ Params[UnitIndex], this.GeoUnit }
+				{ Params[UnitIndex], this.GeoUnit },
+				{ Params[DistanceTypeIndex], this.DistanceType }
 			};
 		}
 	}
@@ -55,7 +59,9 @@ public class SortGeoDistanceDescriptor<T> : SortDescriptorBase<T, SortGeoDistanc
 		IEnumerable<string> IGeoDistanceSort.Points { get; set; }
 
 		GeoUnit? IGeoDistanceSort.GeoUnit { get; set; }
-	
+
+		GeoDistance? IGeoDistanceSort.DistanceType { get; set; }
+
 		public SortGeoDistanceDescriptor<T> PinTo(string geoLocationHash)
 		{
 			geoLocationHash.ThrowIfNullOrEmpty("geoLocationHash");
@@ -93,6 +99,13 @@ public SortGeoDistanceDescriptor<T> Unit(GeoUnit unit)
 			return this;
 		}
 
+		public SortGeoDistanceDescriptor<T> DistanceType(GeoDistance distanceType)
+		{
+			distanceType.ThrowIfNull("distanceType");
+			Self.DistanceType = distanceType;
+			return this;
+		}
+
 		public SortGeoDistanceDescriptor<T> OnField(string field)
 		{
 			Self.Field = field;
@@ -129,7 +142,8 @@ object ICustomJson.GetCustomJson()
 				{ GeoDistanceSort.Params[GeoDistanceSort.MissingIndex], Self.Missing },
 				{ GeoDistanceSort.Params[GeoDistanceSort.ModeIndex], Self.Mode},
 				{ GeoDistanceSort.Params[GeoDistanceSort.OrderIndex], Self.Order },
-				{ GeoDistanceSort.Params[GeoDistanceSort.UnitIndex], Self.GeoUnit }
+				{ GeoDistanceSort.Params[GeoDistanceSort.UnitIndex], Self.GeoUnit },
+				{ GeoDistanceSort.Params[GeoDistanceSort.DistanceTypeIndex], Self.DistanceType }
 			};
 		}
 	}

src/Tests/Nest.Tests.Unit/Search/Sorting/SortTests.cs

@@ -211,6 +211,7 @@ public void TestSortGeo()
 					.PinTo(40, -70)
 					.Unit(GeoUnit.Kilometers)
 					.Mode(SortMode.Max)
+					.DistanceType(GeoDistance.Arc)
 				);
 			var json = TestElasticClient.Serialize(s);
 			var expected = @"
@@ -224,7 +225,8 @@ public void TestSortGeo()
 						 missing: ""_last"",
 						 mode: ""max"",
 						 order: ""desc"",
-						 unit: ""km""
+						 unit: ""km"",
+                         distance_type: ""arc""
 					  }
 					}
                   ]