mixtape/zero/Rendering/RazorRenderer.cs

using Microsoft.AspNetCore.Html;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Abstractions;
using Microsoft.AspNetCore.Mvc.ModelBinding;
using Microsoft.AspNetCore.Mvc.Razor;
using Microsoft.AspNetCore.Mvc.RazorPages;
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.AspNetCore.Mvc.ViewEngines;
using Microsoft.AspNetCore.Mvc.ViewFeatures;
using Microsoft.AspNetCore.Routing;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Options;
using System.Diagnostics;
using System.IO;
using System.Text.Encodings.Web;

namespace zero.Rendering;

public class RazorRenderer : IRazorRenderer, IDisposable
{
  protected IRazorViewEngine ViewEngine { get; set; }

  protected IRazorPageActivator PageActivator { get; set; }

  protected ITempDataDictionaryFactory TempDataDictionaryFactory { get; set; }

  protected IModelMetadataProvider ModelMetadataProvider { get; set; }

  protected IHttpContextAccessor HttpContextAccessor { get; set; }

  protected IServiceScope ServiceScope { get; set; }

  protected HtmlHelperOptions HtmlHelperOptions { get; set; }


  public RazorRenderer(IRazorViewEngine viewEngine, IRazorPageActivator pageActivator, IHttpContextAccessor httpContextAccessor, ITempDataDictionaryFactory tempDataDictionaryFactory, 
    IModelMetadataProvider modelMetadataProvider, IServiceProvider serviceProvider, IOptions<MvcViewOptions> mvcHelperOptions)
  {
    ViewEngine = viewEngine;
    PageActivator = pageActivator;
    HttpContextAccessor = httpContextAccessor;
    TempDataDictionaryFactory = tempDataDictionaryFactory;
    ModelMetadataProvider = modelMetadataProvider;
    ServiceScope = serviceProvider.CreateScope();
    HtmlHelperOptions = mvcHelperOptions.Value.HtmlHelperOptions;
  }


  /// <summary>
  /// Renders a razor component to a string
  /// </summary>
  public async Task<string> ComponentAsync<T>(object args = null) where T : ViewComponent
  {
    return await ComponentAsync(typeof(T), args);
  }


  /// <summary>
  /// Renders a razor component to a string
  /// </summary>
  public async Task<string> ComponentAsync(Type componentType, object args = null)
  {
    return await ComponentAsync(componentType, BuildActionContext(), args);
  }


  /// <summary>
  /// Renders a razor component to a string
  /// </summary>
  public async Task<string> ComponentAsync(string componentName, object args = null)
  {     
    return await ComponentAsync(componentName, BuildActionContext(), args);
  }


  /// <summary>
  /// Renders a razor component to a string
  /// </summary>
  public async Task<string> ComponentAsync<T>(ActionContext context, object args = null) where T : ViewComponent
  {
    return await ComponentAsync(typeof(T), context, args);
  }


  /// <summary>
  /// Renders a razor component to a string
  /// </summary>
  public async Task<string> ComponentAsync(Type componentType, ActionContext context, object args = null)
  {
    IViewComponentHelper viewComponentHelper = context.HttpContext.RequestServices.GetRequiredService<IViewComponentHelper>();
      
    using StringWriter stringWriter = new();

    ViewContext viewContext = BuildViewContext(context, stringWriter);

    (viewComponentHelper as IViewContextAware)?.Contextualize(viewContext);
    IHtmlContent result = await viewComponentHelper.InvokeAsync(componentType, args);

    result.WriteTo(stringWriter, HtmlEncoder.Default);
    await stringWriter.FlushAsync();
    return stringWriter.ToString();
  }


  /// <summary>
  /// Renders a razor component to a string
  /// </summary>
  public async Task<string> ComponentAsync(string componentName, ActionContext context, object args = null)
  {
    IViewComponentHelper viewComponentHelper = context.HttpContext.RequestServices.GetRequiredService<IViewComponentHelper>();
      
    using StringWriter stringWriter = new();

    ViewContext viewContext = BuildViewContext(context, stringWriter);

    (viewComponentHelper as IViewContextAware)?.Contextualize(viewContext);
    IHtmlContent result = await viewComponentHelper.InvokeAsync(componentName, args);

    result.WriteTo(stringWriter, HtmlEncoder.Default);
    await stringWriter.FlushAsync();
    return stringWriter.ToString();
  }


  /// <summary>
  /// Renders a razor page to a string
  /// </summary>
  public async Task<string> PageAsync<T>(T model) where T : PageModel
  {
    IRazorPage pageResult = FindPage(model.PageContext, model.PageContext.ActionDescriptor.RelativePath);

    using StringWriter stringWriter = new();

    RazorView view = new RazorView(ViewEngine, PageActivator, new List<IRazorPage>(), pageResult, HtmlEncoder.Default, new DiagnosticListener("ViewRenderService"));

    ViewContext viewContext = BuildViewContext(model.PageContext, stringWriter, view);
    viewContext.RouteData = model.RouteData;
    viewContext.ViewData = model.ViewData;

    Microsoft.AspNetCore.Mvc.RazorPages.Page razorPage = (Microsoft.AspNetCore.Mvc.RazorPages.Page)pageResult;
    razorPage.PageContext = model.PageContext;
    razorPage.ViewContext = viewContext;

    PageActivator.Activate(razorPage, viewContext);

    await razorPage.ExecuteAsync();
    await stringWriter.FlushAsync();

    return stringWriter.ToString();
  }


  /// <summary>
  /// Renders a razor view to a string
  /// </summary>
  public async Task<string> ViewAsync(string view, object model = null, Action<ViewContext> onBeforeRender = null)
  {
    return await ViewAsync(BuildActionContext(), view, model, onBeforeRender);
  }


  /// <summary>
  /// Renders a razor view to a string
  /// </summary>
  public async Task<string> ViewAsync(ActionContext context, string view, object model = null, Action<ViewContext> onBeforeRender = null)
  {
    IView viewResult = FindView(context, view);

    await using StringWriter stringWriter = new();

    ViewContext viewContext = BuildViewContext(context, stringWriter, viewResult);
    viewContext.RouteData = context.RouteData;
    viewContext.ViewData.Model = model;

    onBeforeRender?.Invoke(viewContext);

    await viewResult.RenderAsync(viewContext);
    await stringWriter.FlushAsync();

    return stringWriter.ToString();
  }


  /// <inheritdoc />
  public void Dispose()
  {
    ServiceScope?.Dispose();
  }


  /// <summary>
  /// Build the view context
  /// </summary>
  protected virtual ViewContext BuildViewContext(ActionContext context, StringWriter writer, IView view = null)
  {
    ViewDataDictionary viewData = new(ModelMetadataProvider, context.ModelState); // result.ViewData ?? new ViewData...;
    ITempDataDictionary tempData = TempDataDictionaryFactory.GetTempData(context.HttpContext); //  result.TempData ?? TempData...;

    return new ViewContext(context, view ?? NullView.Instance, viewData, tempData, writer, HtmlHelperOptions);
  }


  /// <summary>
  /// Builds a new view context
  /// </summary>
  protected virtual ActionContext BuildActionContext()
  {
    HttpContext context = GetHttpContext();
    RouteData routeData = context.GetRouteData();
    return new ActionContext(context, routeData, new ActionDescriptor());
  }


  /// <summary>
  /// Get HTTP context or mock one
  /// </summary>
  protected virtual HttpContext GetHttpContext()
  {
    HttpContext context = HttpContextAccessor.HttpContext;
    context ??= new DefaultHttpContext() 
    { 
      RequestServices = ServiceScope.ServiceProvider 
    };

    return context;
  }


  /// <summary>
  /// Tries to find a view
  /// </summary>
  protected virtual IView FindView(ActionContext actionContext, string viewName)
  {
    ViewEngineResult getViewResult = ViewEngine.GetView(executingFilePath: null, viewPath: viewName, isMainPage: false);
    if (getViewResult.Success)
    {
      return getViewResult.View;
    }

    ViewEngineResult findViewResult = ViewEngine.FindView(actionContext, viewName, isMainPage: false);
    if (findViewResult.Success)
    {
      return findViewResult.View;
    }

    IEnumerable<string> searchedLocations = getViewResult.SearchedLocations.Concat(findViewResult.SearchedLocations);
    string errorMessage = String.Join(Environment.NewLine, new[] { $"Unable to find view '{viewName}'. The following locations were searched:" }.Concat(searchedLocations));

    throw new InvalidOperationException(errorMessage);
  }


  /// <summary>
  /// Tries to find a page
  /// </summary>
  protected virtual IRazorPage FindPage(ActionContext actionContext, string pageName)
  {
    RazorPageResult getPageResult = ViewEngine.GetPage(executingFilePath: null, pagePath: pageName);
    if (getPageResult.Page != null)
    {
      return getPageResult.Page;
    }

    RazorPageResult findPageResult = ViewEngine.FindPage(actionContext, pageName: pageName);
    if (findPageResult.Page != null)
    {
      return findPageResult.Page;
    }

    IEnumerable<string> searchedLocations = getPageResult.SearchedLocations.Concat(findPageResult.SearchedLocations);
    string errorMessage = String.Join(Environment.NewLine, new[] { $"Unable to find page '{pageName}'. The following locations were searched:" }.Concat(searchedLocations));

    throw new InvalidOperationException(errorMessage);
  }


  class GenericController : ControllerBase { }


  class NullView : IView
  {
    public static readonly NullView Instance = new NullView();

    public string Path => string.Empty;

    public Task RenderAsync(ViewContext context)
    {
      if (context == null)
      {
        throw new ArgumentNullException(nameof(context));
      }

      return Task.CompletedTask;
    }
  }

}


public interface IRazorRenderer
{
  /// <summary>
  /// Renders a razor component to a string
  /// </summary>
  Task<string> ComponentAsync<T>(object args = null) where T : ViewComponent;

  /// <summary>
  /// Renders a razor component to a string
  /// </summary>
  Task<string> ComponentAsync(Type componentType, object args = null);

  /// <summary>
  /// Renders a razor component to a string
  /// </summary>
  Task<string> ComponentAsync(string componentName, object args = null);

  /// <summary>
  /// Renders a razor component to a string
  /// </summary>
  Task<string> ComponentAsync<T>(ActionContext context, object args = null) where T : ViewComponent;

  /// <summary>
  /// Renders a razor component to a string
  /// </summary>
  Task<string> ComponentAsync(Type componentType, ActionContext context, object args = null);

  /// <summary>
  /// Renders a razor component to a string
  /// </summary>
  Task<string> ComponentAsync(string componentName, ActionContext context, object args = null);

  /// <summary>
  /// Renders a razor page to a string
  /// </summary>
  Task<string> PageAsync<T>(T model) where T : PageModel;

  /// <summary>
  /// Renders a razor view to a string
  /// </summary>
  Task<string> ViewAsync(string view, object model = null, Action<ViewContext> onBeforeRender = null);

  /// <summary>
  /// Renders a razor view to a string
  /// </summary>
  Task<string> ViewAsync(ActionContext context, string view, object model = null, Action<ViewContext> onBeforeRender = null);
}