HtmlHelperExtensions.cs

public static class HtmlHelperExtensions
{
    private static readonly char Separator = '/';
    private static readonly string TemplateFolder = HttpContext.Current.Server.MapPath("~/App/templates");
    private static readonly IViewEngine ViewEngine = new HandlebarsRazorViewEngine();

    public static MvcHtmlString RenderEmber(this HtmlHelper helper, string path = "", bool noTemplateName = false)
    {
        if (HttpRuntime.Cache[path] == null)
        {
            var builder = new StringBuilder();

            string absolutePath;
            string templateName = "";
            if (string.IsNullOrEmpty(path))
            {
                absolutePath = TemplateFolder;
            }
            else
            {
                templateName = path.Replace("\\", Separator.ToString());
                absolutePath = Path.Combine(TemplateFolder, path);
            }

            if (File.Exists(absolutePath))
            {
                int fileExtensionPosition = templateName.LastIndexOf('.');
                if (fileExtensionPosition > 0)
                {
                    templateName = templateName.Substring(0, fileExtensionPosition);
                }

                AppendFileTemplate(builder, helper, templateName, null, null, new FileInfo(absolutePath), noTemplateName);

                HttpRuntime.Cache.Insert(path, new MvcHtmlString(builder.ToString()), new CacheDependency(absolutePath));
            }
            else
            {
                if (Directory.Exists(absolutePath))
                {
                    if (templateName.Length > 0 && templateName[templateName.Length - 1] != Separator)
                    {
                        templateName += Separator;
                    }
                    List<string> dependencyList = new List<string>();

                    AppendDirectoryTemplates(builder, helper, templateName, "", new DirectoryInfo(absolutePath), dependencyList);

                    var result = new MvcHtmlString(builder.ToString());
                    HttpRuntime.Cache.Insert(path, result, new CacheDependency(dependencyList.ToArray()));
                }
                else
                {
                    return new MvcHtmlString(""); //nothing is found, return empty string and do not cache
                }
            }
        }

        return HttpRuntime.Cache[path] as MvcHtmlString;
    }

    private static void AppendDirectoryTemplates(StringBuilder builder, HtmlHelper helper, string templateName, string relativeDirName, DirectoryInfo rootDirectory, List<string> dependencyList)
    {
        dependencyList.Add(rootDirectory.FullName);

        var newSubRelativeDirName = relativeDirName;
        if (!string.IsNullOrEmpty(newSubRelativeDirName))
        {
            newSubRelativeDirName = newSubRelativeDirName + Separator;
        }

        foreach (DirectoryInfo subDir in rootDirectory.GetDirectories())
        {
            AppendDirectoryTemplates(builder, helper, templateName, newSubRelativeDirName + subDir.Name, subDir, dependencyList);
        }

        foreach (FileInfo templateFile in rootDirectory.GetFiles("*.hbs"))
        {
            string subtemplateName = templateFile.Name;
            int fileExtensionPosition = subtemplateName.LastIndexOf('.');
            if (fileExtensionPosition > 0)
            {
                subtemplateName = subtemplateName.Substring(0, fileExtensionPosition);
            }
            if (relativeDirName.Length > 0 && relativeDirName[relativeDirName.Length - 1] != Separator)
            {
                relativeDirName += Separator;
            }
            AppendFileTemplate(builder, helper, templateName, relativeDirName, subtemplateName, templateFile);
        }
    }

    private static void AppendFileTemplate(StringBuilder builder, HtmlHelper helper, string templateName, string relativeDirName, string subtemplateName, FileInfo templateFile, bool noTemplateName = false)
    {
        if (templateFile.Extension.ToLowerInvariant().StartsWith(".htm"))
        {
            //for .html/.htm* files, we'll simply append the content
            var content = File.ReadAllText(Path.Combine(Path.Combine(templateName, relativeDirName), subtemplateName));
            builder.Append(content);
            return;
        }
        var fullTemplateName = templateName + relativeDirName + subtemplateName;

        //for other template files, we treate them as x-handlebars script type
        if (noTemplateName)
        {
            builder.AppendLine("<script type=\"text/x-handlebars\">");
        }
        else
        {
            builder.AppendLine("<script type=\"text/x-handlebars\" data-template-name=\"" + fullTemplateName + "\">");
        }

        var controllerContext = new ControllerContext(helper.ViewContext.HttpContext, new RouteData(), helper.ViewContext.Controller);
        controllerContext.RouteData.Values["controller"] = string.IsNullOrEmpty(relativeDirName) ? "Home" : Path.GetDirectoryName(relativeDirName);
        var result = ViewEngine.FindView(controllerContext, subtemplateName, null, false);
        var stringWriter = new StringWriter(builder);
        var viewContext = new ViewContext(controllerContext, result.View, new ViewDataDictionary(), new TempDataDictionary(), stringWriter);
        result.View.Render(viewContext, stringWriter);

        builder.AppendLine("</script>");
    }

}