Update handlebars code to support Regex.Match (#201) (#202)

* #201

* Handlebars : Linq and JsonPath

* Rename to Regex.Match

* unit test coverage

src/WireMock.Net/Transformers/HandleBarsLinq.cs

@@ -0,0 +1,88 @@
+using System;
+using System.Linq;
+using System.Linq.Dynamic.Core;
+using System.Linq.Dynamic.Core.Exceptions;
+using HandlebarsDotNet;
+using Newtonsoft.Json.Linq;
+using WireMock.Util;
+using WireMock.Validation;
+
+namespace WireMock.Transformers
+{
+    internal static class HandleBarsLinq
+    {
+        public static void Register()
+        {
+            Handlebars.RegisterHelper("Linq", (writer, context, arguments) =>
+            {
+                (JToken valueToProcess, string linqStatement) = ParseArguments(arguments);
+
+                try
+                {
+                    object result = ExecuteDynamicLinq(valueToProcess, linqStatement);
+                    writer.WriteSafeString(result);
+                }
+                catch (ParseException)
+                {
+                    // Ignore ParseException and return
+                    return;
+                }
+            });
+
+            Handlebars.RegisterHelper("Linq", (writer, options, context, arguments) =>
+            {
+                (JToken valueToProcess, string linqStatement) = ParseArguments(arguments);
+
+                try
+                {
+                    var result = ExecuteDynamicLinq(valueToProcess, linqStatement);
+                    options.Template(writer, result);
+                }
+                catch (ParseException)
+                {
+                    // Ignore ParseException and return
+                    return;
+                }
+            });
+        }
+
+        private static dynamic ExecuteDynamicLinq(JToken value, string linqStatement)
+        {
+            // Convert a single object to a Queryable JObject-list with 1 entry.
+            var queryable1 = new[] { value }.AsQueryable();
+
+            // Generate the DynamicLinq select statement.
+            string dynamicSelect = JsonUtils.GenerateDynamicLinqStatement(value);
+
+            // Execute DynamicLinq Select statement.
+            var queryable2 = queryable1.Select(dynamicSelect);
+
+            // Execute the Select(...) method and get first result with FirstOrDefault().
+            return queryable2.Select(linqStatement).FirstOrDefault();
+        }
+
+        private static (JToken valueToProcess, string linqStatement) ParseArguments(object[] arguments)
+        {
+            Check.Condition(arguments, args => args.Length == 2, nameof(arguments));
+            Check.NotNull(arguments[0], "arguments[0]");
+            Check.NotNullOrEmpty(arguments[1] as string, "arguments[1]");
+
+            JToken valueToProcess;
+            switch (arguments[0])
+            {
+                case string jsonAsString:
+                    valueToProcess = new JValue(jsonAsString);
+                    break;
+
+                case JToken jsonAsJObject:
+                    valueToProcess = jsonAsJObject;
+                    break;
+
+                default:
+                    throw new NotSupportedException($"The value '{arguments[0]}' with type '{arguments[0]?.GetType()}' cannot be used in Handlebars Linq.");
+            }
+
+            return (valueToProcess, arguments[1] as string);
+        }
+    }
+}