I have an HTML string. I need to change the string to add links to all header tags. For example,

First HTML

<h1> Title 1 </h1>
<p>Lorem ipsum dolor...</p>
<h2> Title 2 </h2>
<h2> Title 2 Different </h2>

The HTML I Want

    <div><a  href="#my_slugged__link_by_title"> <h1> Title 1 </h1> </a> </div>
    <p>Lorem ipsum dolor...</p>
    <div><a  href="#my_slugged__link_by_title_2"> <h2> Title 2 </h2> </a> </div>
     <div><a  href="#my_slugged__link_by_title_2_different"> <h2> Title 2 Different </h2> </a> </div>

**my_slugged__link_by_title** --> I would like to create hash permalinks by Titles. (h1, h2, ...)

For example, the newdescription is my HTML string.

//Replace titles for adding backlinks
                newDescription = "<h2> TEST </h2> <h2> TEST 2</h2>";

This is worked for one string

var oneTitle = Regex.Match(newDescription, @"<h2> (. ?)</h2>").Groups[1].Value

How can I replace and get all of them?

            foreach (var item in Regex.Match(newDescription, @"<h2> (. ?)</h2>").Groups)
            {
                string header_link = "<div class=\"blog_header__backlink_item\"><a href=\"#"   item   "\"><i class=\"fas fa-link\"></i></a></div>";
                newDescription = newDescription.Replace("<h2>", header_link   "<h2>");
            }

CodePudding user response：

You should not try to parse or replace HTML with string methods, even with regex this task is too complicated if the HTML get's complex. Use HtmlAgilityPack (Demo):

string html = @"<h1> Title 1 </h1>
<p>Lorem ipsum dolor...</p>
<h2> Title 2 </h2>
<h2> Title 2 Different </h2>";

string resultHtml = ReplaceHeaderHtml(html);

private static string ReplaceHeaderHtml(string html)
{
    var doc = new HtmlDocument();
    doc.LoadHtml(html);
    var xpath = "//*[self::h1 or self::h2 or self::h3 or self::h4]";
    HtmlNodeCollection headers = doc.DocumentNode.SelectNodes(xpath);
    if (headers == null || headers.Count == 0)
        return html;

    var headerList = headers
        .Where(node => !"a".Equals(node.PreviousSibling?.OriginalName, StringComparison.InvariantCultureIgnoreCase))
        .ToList();

    if (!headerList.Any())
        return html;

    for(int i = 0; i < headerList.Count; i  )
    {
        var header = headerList[i];
        var parentNode = header.ParentNode;
        int headerIndex = parentNode.ChildNodes.IndexOf(header);
        HtmlNode div = doc.CreateElement("div");
        HtmlNode anchor = doc.CreateElement("a");

        string href;
        switch(header.OriginalName)
        {
            case "h1": href = "#my_slugged__link_by_title"; break;
            case "h2": href = "#my_slugged__link_by_title_2"; break;
            case "h3": href = "#my_slugged__link_by_title_3"; break;
            default: href = "#my_slugged__link_by_title"; break;
        }

        anchor.Attributes.Add("class", "header_link");
        anchor.Attributes.Add("href", href);

        div.ChildNodes.Add(anchor);
        div.ChildNodes.Add(header);
        parentNode.ChildNodes.Remove(header);
        parentNode.ChildNodes.Insert(headerIndex, div);
    }

    return doc.DocumentNode.OuterHtml;
}