Custom TagHelper for returning active class for menu items

LiTagHelper.cs

using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.AspNetCore.Mvc.ViewFeatures;
using Microsoft.AspNetCore.Razor.TagHelpers;

namespace MyApplication.Web.TagHelpers
{
    /// <summary>
    /// Reference: https://stackoverflow.com/questions/20410623/how-to-add-active-class-to-html-actionlink-in-asp-net-mvc
    /// Item: Easy ASP.NET 3.0 and TagHelpers
    /// </summary>
    [HtmlTargetElement("li", Attributes = "active-when")]
    public class LiTagHelper : TagHelper
    {
        public string ActiveWhen { get; set; }

        [ViewContext]
        [HtmlAttributeNotBound]
        public ViewContext ViewContextData { get; set; }

        public override void Process(TagHelperContext context, TagHelperOutput output)
        {
            if (ActiveWhen == null)
            {
                return;
            }

            var targetController = ActiveWhen.Split("/")[1].ToLower();
            var targetAction = ActiveWhen.Split("/")[2].ToLower();

            var page = ViewContextData.RouteData.Values["page"].ToString().ToLower();
            var currentController = page.Split("/")[1].ToLower();
            var currentAction = page.Split("/")[2].ToLower();

            if (currentController.Equals(targetController) && currentAction.Equals(targetAction))
            {
                if (output.Attributes.ContainsName("class"))
                {
                    output.Attributes.SetAttribute("class", $"{output.Attributes["class"].Value} active");
                }
                else
                {
                    output.Attributes.SetAttribute("class", "active");
                }
            }
        }
    }
}