Automap/Infer mapping for TimeSpan and TimeSpan? property types as long (ticks)

Closes #1705

Author: russcam

Diff for: src/Nest/CommonAbstractions/SerializationBehavior/ElasticContractResolver.cs

@@ -42,8 +42,14 @@ protected override JsonContract CreateContract(Type objectType)
 				contract.Converter = new VerbatimDictionaryKeysJsonConverter();
 			else if (objectType == typeof(ServerError))
 				contract.Converter = new ServerErrorJsonConverter();
-			else if (objectType == typeof(DateTime) || objectType == typeof(DateTime?))
+			else if (objectType == typeof(DateTime) || 
+					 objectType == typeof(DateTime?) ||
+					 objectType == typeof(DateTimeOffset) ||
+					 objectType == typeof(DateTimeOffset?))
 				contract.Converter = new IsoDateTimeConverter();
+			else if (objectType == typeof(TimeSpan) ||
+					 objectType == typeof(TimeSpan?))
+				contract.Converter = new TimeSpanConverter();
 
 			if (this._contractConverters.HasAny())
 			{

Diff for: src/Nest/CommonAbstractions/SerializationBehavior/GenericJsonConverters/TimeSpanConverter.cs

@@ -0,0 +1,38 @@
+using System;
+using Newtonsoft.Json;
+
+namespace Nest
+{
+	internal class TimeSpanConverter : JsonConverter
+	{
+		public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
+		{
+			if (value == null)
+				writer.WriteNull();
+			else
+			{
+				var timeSpan = (TimeSpan) value;
+				writer.WriteValue(timeSpan.Ticks);
+			}
+		}
+
+		public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
+		{
+			if (reader.TokenType == JsonToken.Null)
+			{
+				if (!objectType.IsGeneric() || objectType.GetGenericTypeDefinition() != typeof (Nullable<>))
+					throw new JsonSerializationException($"Cannot convert null value to {objectType}.");
+
+				return null;
+			}
+
+			if (reader.TokenType != JsonToken.Integer)
+				throw new JsonSerializationException($"Cannot convert token of type {reader.TokenType} to {objectType}.");
+
+			return new TimeSpan((long)reader.Value);
+		}
+
+		public override bool CanConvert(Type objectType) => 
+			objectType == typeof (TimeSpan) || objectType == typeof (TimeSpan?);
+	}
+}

Diff for: src/Nest/Mapping/Visitor/PropertyWalker.cs

@@ -106,6 +106,7 @@ private IProperty InferProperty(Type type)
 						return new NumberProperty(NumberType.Byte);
 					case "Int64":
 					case "UInt32":
+					case "TimeSpan":
 						return new NumberProperty(NumberType.Long);
 					case "Single":
 						return new NumberProperty(NumberType.Float);

Diff for: src/Tests/Framework/MockData/CommitActivity.cs

@@ -11,6 +11,7 @@ public class CommitActivity
 		public long SizeInBytes { get; set; }
 		public double ConfidenceFactor { get; set; }
 		public Developer Committer { get; set; }
+		public TimeSpan? Duration { get; set; }
 
 		public static Faker<CommitActivity> Generator { get; } =
 			new Faker<CommitActivity>()
@@ -20,6 +21,16 @@ public class CommitActivity
 				.RuleFor(p => p.Message, p => p.Lorem.Paragraph(Gimme.Random.Number(1, 3)))
 				.RuleFor(p => p.SizeInBytes, p => p.Random.Number(0, 100000))
 				.RuleFor(p => p.ConfidenceFactor, p => p.Random.Double())
+				.RuleFor(p => p.Duration, p => p.Random.ArrayElement(new TimeSpan?[]
+				{
+					TimeSpan.MinValue,
+					TimeSpan.MaxValue, 
+					null,
+					TimeSpan.Zero, 
+					TimeSpan.FromMinutes(7.5),
+					TimeSpan.FromHours(4.23),
+					TimeSpan.FromDays(5),
+				}))
 			;
 	}
 }

Diff for: src/Tests/Mapping/Types/Core/Number/NumberMappingTests.cs

@@ -43,6 +43,8 @@ public class NumberTest
         public double Double { get; set; }
 
         public decimal Decimal { get; set; }
+
+		public TimeSpan TimeSpan { get; set; }
 	}
 
 	public class NumberMappingTests
@@ -114,7 +116,11 @@ public class NumberMappingTests
                 @decimal = new
                 {
                     type = "double"
-                }
+                },
+				timeSpan = new
+				{
+					type = "long"
+				}
 			}
 		};
 
@@ -174,8 +180,13 @@ public class NumberMappingTests
             )
 	        .Number(d => d
 	            .Name(o => o.Double)
-	        ).Number(d => d
+	        )
+			.Number(d => d
 	            .Name(o => o.Decimal)
-	        );
+	        )
+			.Number(d => d
+	            .Name(o => o.TimeSpan)
+				.Type(NumberType.Long)
+			);
 	}
 }