Add highlight option to phrase suggester

Closes #1007

Author: gmarz

src/Nest/DSL/Suggest/PhraseSuggestDescriptor.cs

@@ -29,7 +29,10 @@ public interface IPhraseSuggester : ISuggester
 		[JsonProperty(PropertyName = "direct_generator")]
 		IEnumerable<IDirectGenerator> DirectGenerator { get; set; }
 
-		[JsonProperty("collate")]
+		[JsonProperty(PropertyName = "highlight")]
+		IPhraseSuggestHighlight Highlight { get; set; }
+
+		[JsonProperty(PropertyName = "collate")]
 		IPhraseSuggestCollate Collate { get; set; }
 	}
 
@@ -41,7 +44,7 @@ public class PhraseSuggester : Suggester, IPhraseSuggester
 		public decimal? MaxErrors { get; set; }
 		public char? Separator { get; set; }
 		public IEnumerable<IDirectGenerator> DirectGenerator { get; set; }
-
+		public IPhraseSuggestHighlight Highlight { get; set; }
 		public IPhraseSuggestCollate Collate { get; set; }
 	}
 
@@ -61,6 +64,8 @@ public class PhraseSuggestDescriptor<T> : BaseSuggestDescriptor<T>, IPhraseSugge
 
 		IEnumerable<IDirectGenerator> IPhraseSuggester.DirectGenerator { get; set; }
 
+		IPhraseSuggestHighlight IPhraseSuggester.Highlight { get; set; }
+
 		IPhraseSuggestCollate IPhraseSuggester.Collate { get; set; }
 
 		public PhraseSuggestDescriptor<T> Text(string text)
@@ -129,6 +134,13 @@ public PhraseSuggestDescriptor<T> DirectGenerator(params Func<DirectGeneratorDes
 			return this;
 		}
 
+		public PhraseSuggestDescriptor<T> Highlight(Func<PhraseSuggestHighlightDescriptor, PhraseSuggestHighlightDescriptor> highlightDescriptor)
+		{
+			var selector = highlightDescriptor(new PhraseSuggestHighlightDescriptor());
+			Self.Highlight = selector.Highlight;
+			return this;
+		}
+
 		public PhraseSuggestDescriptor<T> Collate(Func<PhraseSuggestCollateDescriptor<T>, PhraseSuggestCollateDescriptor<T>> collateDescriptor)
 		{
 			var selector = collateDescriptor(new PhraseSuggestCollateDescriptor<T>());

src/Nest/DSL/Suggest/PhraseSuggestHighlightDescriptor.cs

@@ -0,0 +1,47 @@
+using Nest.Resolvers.Converters;
+using Newtonsoft.Json;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace Nest
+{
+	[JsonObject(MemberSerialization = MemberSerialization.OptIn)]
+	public interface IPhraseSuggestHighlight
+	{
+		[JsonProperty(PropertyName = "pre_tag")]
+		string PreTag { get; set; }
+
+		[JsonProperty(PropertyName = "post_tag")]
+		string PostTag { get; set; }
+	}
+
+	public class PhraseSuggestHighlight : IPhraseSuggestHighlight
+	{
+		public string PreTag { get; set; }
+
+		public string PostTag { get; set; }
+	}
+
+	public class PhraseSuggestHighlightDescriptor : IPhraseSuggestHighlight
+	{
+		internal IPhraseSuggestHighlight Highlight = new PhraseSuggestHighlight();
+
+		string IPhraseSuggestHighlight.PreTag { get; set; }
+
+		string IPhraseSuggestHighlight.PostTag { get; set; }
+
+		public PhraseSuggestHighlightDescriptor PreTag(string preTag)
+		{
+			this.Highlight.PreTag = preTag;
+			return this;
+		}
+		
+		public PhraseSuggestHighlightDescriptor PostTag(string postTag)
+		{
+			this.Highlight.PostTag = postTag;
+			return this;
+		}
+	}
+}

src/Nest/Nest.csproj

@@ -260,6 +260,7 @@
     <Compile Include="DSL\Suggest\Context\GeoLocationSuggestDescriptor.cs" />
     <Compile Include="DSL\Suggest\Context\ISuggestContext.cs" />
     <Compile Include="DSL\SearchTemplateDescriptor.cs" />
+    <Compile Include="DSL\Suggest\PhraseSuggestHighlightDescriptor.cs" />
     <Compile Include="DSL\TemplateExistsDescriptor.cs" />
     <Compile Include="Domain\Responses\PingResponse.cs" />
     <Compile Include="Domain\Responses\NodesShutdownResponse.cs" />

src/Tests/Nest.Tests.Unit/Search/suggest/PhraseSuggestTests.cs

@@ -97,6 +97,10 @@ public void PhraseSuggestCollateTest()
 					.Size(1)
 					.GramSize(2)
 					.MaxErrors(0.5m)
+					.Highlight(h => h
+						.PreTag("<em>")
+						.PostTag("</em>")
+					)
 					.Collate(c => c
 						.Query(q => q
 							.Match(m => m
@@ -122,6 +126,10 @@ public void PhraseSuggestCollateTest()
                               ""size"": 1,
 							  ""gram_size"": 2,
                               ""max_errors"": 0.5,
+							  ""highlight"": {
+								""pre_tag"": ""<em>"",
+								""post_tag"": ""</em>""
+							  },
 							  ""collate"": {
 									""query"": {
 										""match"": {