blog3000/Blog3000/Client/Shared/MarkdownViewer.razor.cs

using Ganss.XSS;
using Markdig;
using Markdig.Syntax;
using Microsoft.AspNetCore.Components;
using Blog3000.Shared;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Net.Http;
using System.Threading.Tasks;

namespace Blog3000.Client.Shared
{
    public partial class MarkdownViewer: IDisposable
    {

        public delegate string ImgRefRewriterDelegate(string imgKey, string currentUrl);
        
        [Parameter]
        public string Markdown
        {
            get
            {
                return _markdown;
            }
            set
            {
                _markdown = value;
                MarkdownChanged?.Invoke(this, EventArgs.Empty);
            }
        }

        private string _markdown;
        


        [Parameter]
        public ImgRefRewriterDelegate ImgRefRewriter{ get; set; }


        [Inject]
        private IHtmlSanitizer htmlSanitizer { get; set; }

        private MarkupString HtmlContent { get; set; }

        private event EventHandler MarkdownChanged;

        public void Dispose()
        {
            MarkdownChanged -= MarkdownViewer_MarkdownChanged;
        }

        protected override async Task OnInitializedAsync()
        {
            await Task.Run(() =>
            {
               
            });
            HtmlContent = await FromMarkdown(Markdown);
            MarkdownChanged += MarkdownViewer_MarkdownChanged;
        }

        private async void MarkdownViewer_MarkdownChanged(object sender, EventArgs e)
        {
            HtmlContent = await FromMarkdown(Markdown);
            StateHasChanged();
        }

        private async Task<MarkupString> FromMarkdown(string markdown)
        {
            var mdPipeline = new MarkdownPipelineBuilder().UseAdvancedExtensions().Build();

            var mdoc = Markdig.Markdown.Parse(markdown, mdPipeline);


            Dictionary<string, string> imgGeysByUrls = null;
            if (ImgRefRewriter != null)
            {
                System.Diagnostics.Debug.WriteLine($"*** Rewriter active");
                imgGeysByUrls ??= new Dictionary<string, string>();
                foreach (var r in mdoc.GetLinkReferenceDefinitions().Links)
                {
                    System.Diagnostics.Debug.WriteLine($"Found {r.Key} => {r.Value.Url}");
                    if (r.Value != null && r.Value.Url != null)
                    {
                        imgGeysByUrls.Add(r.Value.Url, r.Key);
                    }
                }
            }

            
            //var html = Markdig.Markdown.ToHtml(markdown, mdPipeline);

            var writer = new StringWriter();            
            var renderer = new Markdig.Renderers.HtmlRenderer(writer);
            if (ImgRefRewriter != null)
            {
                renderer.LinkRewriter += (a) =>
                {                    
                    string imgKey;
                    if (imgGeysByUrls.TryGetValue(a, out imgKey))
                    {
                        return ImgRefRewriter(imgKey, a);                                               
                    }
                    return a;
                };
            }
            mdPipeline.Setup(renderer);            
            renderer.Render(mdoc);
            var html = writer.ToString();
            //System.Diagnostics.Debug.WriteLine(html);
            html = htmlSanitizer.Sanitize(html);            
            return new MarkupString(html);

        }

     
    }   
}