Add support for condition token filter

src/Nest/Analysis/TokenFilters/ConditionTokenFilter.cs

@@ -0,0 +1,66 @@
+using System;
+using System.Collections.Generic;
+using Newtonsoft.Json;
+
+namespace Nest
+{
+	/// <summary>
+	/// The conditional token filter takes a predicate script and a list of subfilters, and
+	/// only applies the subfilters to the current token if it matches the predicate.
+	/// </summary>
+	public interface IConditionTokenFilter : ITokenFilter
+	{
+		/// <summary>
+		/// a predicate script that determines whether or not the filters will be applied
+		/// to the current token.  Note that only inline scripts are supported
+		/// </summary>
+		[JsonProperty("script")]
+		IScript Script { get; set; }
+
+		/// <summary>
+		///a chain of token filters to apply to the current token if the predicate
+		/// matches. These can be any token filters defined elsewhere in the index mappings.
+		/// </summary>
+		[JsonProperty("filter")]
+		IEnumerable<string> Filters { get; set; }
+	}
+
+	/// <inheritdoc cref="IConditionTokenFilter" />
+	public class ConditionTokenFilter : TokenFilterBase, IConditionTokenFilter
+	{
+		public ConditionTokenFilter() : base("condition") { }
+
+		/// <inheritdoc cref="IConditionTokenFilter.Script" />
+		public IScript Script { get; set; }
+
+		/// <inheritdoc cref="IConditionTokenFilter.Filters" />
+		public IEnumerable<string> Filters { get; set; }
+	}
+
+	/// <inheritdoc cref="IConditionTokenFilter" />
+	public class ConditionTokenFilterDescriptor
+		: TokenFilterDescriptorBase<ConditionTokenFilterDescriptor, IConditionTokenFilter>, IConditionTokenFilter
+	{
+		protected override string Type => "condition";
+
+		IScript IConditionTokenFilter.Script { get; set; }
+		IEnumerable<string> IConditionTokenFilter.Filters { get; set; }
+
+		/// <inheritdoc cref="IConditionTokenFilter.Script" />
+		public ConditionTokenFilterDescriptor Script(Func<ScriptDescriptor, IScript> scriptSelector) =>
+			Assign(a => a.Script = scriptSelector?.Invoke(new ScriptDescriptor()));
+
+		/// <inheritdoc cref="IConditionTokenFilter.Script" />
+		public ConditionTokenFilterDescriptor Script(string predicate) =>
+			Assign(a => a.Script = new InlineScript(predicate));
+
+		/// <inheritdoc cref="IConditionTokenFilter.Filters" />
+		public ConditionTokenFilterDescriptor Filters(params string[] filters) =>
+			Assign(a => a.Filters = filters);
+
+		/// <inheritdoc cref="IConditionTokenFilter.Filters" />
+		public ConditionTokenFilterDescriptor Filters(IEnumerable<string> filters) =>
+			Assign(a => a.Filters = filters);
+
+}
+}

src/Nest/Analysis/TokenFilters/TokenFilters.cs

@@ -225,6 +225,10 @@ public TokenFiltersDescriptor Standard(string name, Func<StandardTokenFilterDesc
 		public TokenFiltersDescriptor Stemmer(string name, Func<StemmerTokenFilterDescriptor, IStemmerTokenFilter> selector) =>
 			Assign(name, selector?.Invoke(new StemmerTokenFilterDescriptor()));
 
+		/// <inheritdoc cref="IConditionTokenFilter" />
+		public TokenFiltersDescriptor Condition(string name, Func<ConditionTokenFilterDescriptor, IConditionTokenFilter> selector) =>
+			Assign(name, selector?.Invoke(new ConditionTokenFilterDescriptor()));
+
 		/// <summary>
 		/// Overrides stemming algorithms, by applying a custom mapping, then protecting these terms from being modified by stemmers. Must be placed
 		/// before any stemming filters.

src/Nest/Indices/Analyze/AnalyzeTokenFilters.cs

@@ -241,6 +241,10 @@ public AnalyzeTokenFiltersDescriptor Standard(Func<StandardTokenFilterDescriptor
 			AssignIfNotNull(selector.InvokeOrDefault(new StandardTokenFilterDescriptor()));
 #pragma warning restore 618
 
+		/// <inheritdoc cref="IConditionTokenFilter" />
+		public AnalyzeTokenFiltersDescriptor Condition(Func<ConditionTokenFilterDescriptor, IConditionTokenFilter> selector) =>
+			AssignIfNotNull(selector?.Invoke(new ConditionTokenFilterDescriptor()));
+
 		/// <summary>
 		/// A filter that stems words (similar to snowball, but with more options).
 		/// </summary>

src/Tests/Tests/Analysis/TokenFilters/TokenFilterTests.cs

@@ -896,8 +896,35 @@ public class NoriPartOfSpeechTests : TokenFilterAssertionBase<NoriPartOfSpeechTe
 			public override string Name => "nori_pos";
 		}
 
+		[SkipVersion("<6.5.0", "Introduced in 6.5.0")]
+		public class ConditionTests : TokenFilterAssertionBase<ConditionTests>
+		{
+			private readonly string _predicate = "token.getTerm().length() < 5";
+
+			public override FuncTokenFilters Fluent => (n, tf) => tf
+				.Condition(n, t => t
+					.Filters("lowercase", "lowercase, porter_stem")
+					.Script(_predicate)
+				);
+
+			public override ITokenFilter Initializer => new ConditionTokenFilter
+			{
+				Filters = new[] { "lowercase", "lowercase, porter_stem" },
+				Script = new InlineScript(_predicate)
+			};
+
+			public override object Json => new
+			{
+				type = "condition",
+				filter = new[] { "lowercase", "lowercase, porter_stem" },
+				script = new { source = _predicate }
+			};
+
+			public override string Name => "condition";
+		}
+
 		[SkipVersion("<6.4.0", "Introduced in 6.4.0")]
-		public class MultiplexerTests : TokenFilterAssertionBase<PhoneticTests>
+		public class MultiplexerTests : TokenFilterAssertionBase<MultiplexerTests>
 		{
 			public override FuncTokenFilters Fluent => (n, tf) => tf
 				.Multiplexer(n, t => t
@@ -913,6 +940,7 @@ public class MultiplexerTests : TokenFilterAssertionBase<PhoneticTests>
 
 			public override object Json => new
 			{
+				type = "multiplexer",
 				filters = new[] { "lowercase", "lowercase, porter_stem" },
 				preserve_original = true
 			};
@@ -921,11 +949,11 @@ public class MultiplexerTests : TokenFilterAssertionBase<PhoneticTests>
 		}
 
 		[SkipVersion("<6.4.0", "Introduced in 6.4.0")]
-		public class RemoveDuplicatesTests : TokenFilterAssertionBase<PhoneticTests>
+		public class RemoveDuplicatesTests : TokenFilterAssertionBase<RemoveDuplicatesTests>
 		{
 			public override FuncTokenFilters Fluent => (n, tf) => tf.RemoveDuplicates(n);
 			public override ITokenFilter Initializer => new RemoveDuplicatesTokenFilter { };
-			public override object Json => new { };
+			public override object Json => new { type = "remove_duplicates" };
 			public override string Name => "dupes";
 		}
 	}