using Microsoft.AspNetCore.Mvc.Razor;
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.AspNetCore.Mvc.ViewEngines;
using Microsoft.AspNetCore.Mvc.ViewFeatures;
using System.IO;
using System.Text;

public static class RazorPageRenderer
{
    public static string RenderRazorPageToString<TModel>(string viewName, TModel model)
    {
        var httpContext = new DefaultHttpContext { RequestServices = YourServiceProvider };
        var actionContext = new ActionContext(httpContext, new RouteData(), new ActionDescriptor());

        var viewEngineResult = YourViewEngine.FindView(actionContext, viewName, false);

        if (!viewEngineResult.Success)
        {
            throw new InvalidOperationException($"Couldn't find view '{viewName}'");
        }

        var view = viewEngineResult.View;
        var viewData = new ViewDataDictionary<TModel>(new EmptyModelMetadataProvider(), new ModelStateDictionary())
        {
            Model = model
        };

        using (var sw = new StringWriter())
        {
            var viewContext = new ViewContext(
                actionContext,
                view,
                viewData,
                new TempDataDictionary(actionContext.HttpContext, YourTempDataProvider),
                sw,
                new HtmlHelperOptions()
            );

            view.RenderAsync(viewContext).GetAwaiter().GetResult();
            return sw.ToString();
        }
    }
}