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/HandleBarsJsonPath.cs

@@ -0,0 +1,75 @@
+using System;
+using System.Linq;
+using HandlebarsDotNet;
+using Newtonsoft.Json;
+using Newtonsoft.Json.Linq;
+using WireMock.Validation;
+
+namespace WireMock.Transformers
+{
+    internal static class HandleBarsJsonPath
+    {
+        public static void Register()
+        {
+            Handlebars.RegisterHelper("JsonPath.SelectToken", (writer, context, arguments) =>
+            {
+                (JObject valueToProcess, string jsonpath) = ParseArguments(arguments);
+
+                try
+                {
+                    var result = valueToProcess.SelectToken(jsonpath);
+                    writer.WriteSafeString(result);
+                }
+                catch (JsonException)
+                {
+                    // Ignore JsonException and return
+                    return;
+                }
+            });
+
+            Handlebars.RegisterHelper("JsonPath.SelectTokens", (writer, options, context, arguments) =>
+            {
+                (JObject valueToProcess, string jsonpath) = ParseArguments(arguments);
+
+                try
+                {
+                    var values = valueToProcess.SelectTokens(jsonpath);
+                    if (values != null)
+                    {
+                        options.Template(writer, values.ToDictionary(value => value.Path, value => value));
+                    }
+                }
+                catch (JsonException)
+                {
+                    // Ignore JsonException and return
+                    return;
+                }
+            });
+        }
+
+        private static (JObject valueToProcess, string jsonpath) 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]");
+
+            JObject valueToProcess;
+
+            switch (arguments[0])
+            {
+                case string jsonAsString:
+                    valueToProcess = JObject.Parse(jsonAsString);
+                    break;
+
+                case JObject jsonAsJObject:
+                    valueToProcess = jsonAsJObject;
+                    break;
+
+                default:
+                    throw new NotSupportedException($"The value '{arguments[0]}' with type '{arguments[0]?.GetType()}' cannot be used in Handlebars JsonPath.");
+            }
+
+            return (valueToProcess, arguments[1] as string);
+        }
+    }
+}