btcpayserver/BTCPayServer/Views/Stores/StoreNavPages.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.AspNetCore.Mvc.ViewFeatures;

namespace BTCPayServer.Views.Stores
{
    public static class StoreNavPages
    {
        public static string ActivePageKey => "ActivePage";
        public static string Index => "Index";
        public static string Checkout => "Checkout experience";

        public static string Tokens => "Tokens";
        public static string Users => "Users";
        public static string UsersNavClass(ViewContext viewContext) => PageNavClass(viewContext, Users);
        public static string TokensNavClass(ViewContext viewContext) => PageNavClass(viewContext, Tokens);

        public static string CheckoutNavClass(ViewContext viewContext) => PageNavClass(viewContext, Checkout);
        public static string IndexNavClass(ViewContext viewContext) => PageNavClass(viewContext, Index);

        public static string PageNavClass(ViewContext viewContext, string page)
        {
            var activePage = viewContext.ViewData["ActivePage"] as string;
            return string.Equals(activePage, page, StringComparison.OrdinalIgnoreCase) ? "active" : null;
        }

        public static void AddActivePage(this ViewDataDictionary viewData, string activePage) => viewData[ActivePageKey] = activePage;
    }
}