WireMock.Net/src/WireMock.Net/Transformers/HandleBarsFile.cs

using HandlebarsDotNet;
using System;
using WireMock.Handlers;
using WireMock.Validation;

namespace WireMock.Transformers
{
    internal static class HandlebarsFile
    {
        public static void Register(IHandlebars handlebarsContext, IFileSystemHandler fileSystemHandler)
        {
            handlebarsContext.RegisterHelper("File", (writer, context, arguments) =>
            {
                string value = ParseArgumentAndReadFileFragment(handlebarsContext, context, fileSystemHandler, arguments);
                writer.Write(value);
            });

            handlebarsContext.RegisterHelper("File", (writer, options, context, arguments) =>
            {
                string value = ParseArgumentAndReadFileFragment(handlebarsContext, context, fileSystemHandler, arguments);
                options.Template(writer, value);
            });
        }

        private static string ParseArgumentAndReadFileFragment(IHandlebars handlebarsContext, dynamic context, IFileSystemHandler fileSystemHandler, object[] arguments)
        {
            Check.Condition(arguments, args => args.Length == 1, nameof(arguments));
            Check.NotNull(arguments[0], "arguments[0]");

            switch (arguments[0])
            {
                case string path:
                    var templateFunc = handlebarsContext.Compile(path);
                    string transformed = templateFunc(context);
                    return fileSystemHandler.ReadResponseBodyAsString(transformed);
            }

            throw new NotSupportedException($"The value '{arguments[0]}' with type '{arguments[0]?.GetType()}' cannot be used in Handlebars File.");
        }
    }
}