namespace System.Web.Mvc.Html
{
    public static class CacheExtension
    {
        public static MvcHtmlString RenderScript(this HtmlHelper helper, string filename, bool asyncLoad = false)
        {
			var fileName = VirtualPathUtility.ToAbsolute(filename);
			var version = GetVersion(helper, filename);
			var async = asyncLoad ? " async='async'" : "";
			var result = String.Format("<script src='{0}{1}' type='text/javascript'{2}></script>", fileName, version, async);
            return MvcHtmlString.Create(result);
        }

        public static MvcHtmlString RenderStyle(this HtmlHelper helper, string filename)
        {
            var version = GetVersion(helper, filename);
            return MvcHtmlString.Create("<link href='" + VirtualPathUtility.ToAbsolute(filename) + version + "' rel='stylesheet' type='text/css'>");
        }

        private static string GetVersion(this HtmlHelper helper, string filename)
        {
            var context = helper.ViewContext.RequestContext.HttpContext;

            if (context.Cache[filename] == null)
            {
                var physicalPath = context.Server.MapPath(filename);
                var version = "?v=" + new IO.FileInfo(physicalPath).LastWriteTime.ToString("yyyyMMddHHmmss");

                context.Cache[filename] = version;

                return version;
            }
            else
            {
                return context.Cache[filename] as string;
            }
        }
    }
}