C# How to inject missing TR & TD in html data

Question

I am jostling for few day to inject missing TR & TD tags in my html programmatically. from this link https://stackoverflow.com/a/18397864/14171304 i found that HtmlAgility pack does this job but i saw HtmlAgility pack adding missing closing tag but it can not add missing opening tag.

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I have a html where high chance that any number of TR & TD could be missing into html data. i am looking for a routine which would inject Table, TR & TD tag if any missing.

my objective is to add/inject missing any opening & closing Table, TR & TD tag in html.

after sanitize html each row (TR) must have same number of TD tag. so want to could max number of TD and if any row(TR) has lesser number of TD tag then add empty tag in the beginning of that TR tag.

This way i tried to inject missing TR & TD tag but no luck. any can help me.

private void button1_Click(object sender, EventArgs e)
        {
            string htmldata = @"<table>
              <tr>
                <th>Company</th>
                <th>Contact</th>
                <th>Country</th>
              </tr>
              
                Alfreds Futterkiste</td>
                <td>Maria Anders</td>
                <td>Germany
              </tr>
              <tr>
                <td>Centro comercial Moctezuma</td>
                <td>Francisco Chang</td>
                <td>Mexico
              </tr>
            </table>";

            string abc = AddMissingHtmlTags(htmldata);
        }

public static string AddMissingHtmlTags(string htmlData)
{
    // Define regular expressions for table, tr, and td tags
    Regex tableRegex = new Regex(@"<table[^>]*>.*?</table>", RegexOptions.IgnoreCase | RegexOptions.Singleline);
    Regex trRegex = new Regex(@"<tr[^>]*>.*?</tr>", RegexOptions.IgnoreCase | RegexOptions.Singleline);
    Regex tdRegex = new Regex(@"<td[^>]*>.*?</td>", RegexOptions.IgnoreCase | RegexOptions.Singleline);

    // Match all table elements in the HTML
    MatchCollection tableMatches = tableRegex.Matches(htmlData);

    foreach (Match tableMatch in tableMatches)
    {
        string tableHtml = tableMatch.Value;

        // Match all tr elements within the table
        MatchCollection trMatches = trRegex.Matches(tableHtml);

        foreach (Match trMatch in trMatches)
        {
            string trHtml = trMatch.Value;

            // If there are no td elements within the tr, add one
            if (!tdRegex.IsMatch(trHtml))
            {
                string newTd = "<td></td>";
                string modifiedTr = trHtml.Insert(trHtml.Length - 5, newTd); // Insert new td before the closing </tr> tag
                htmlData = htmlData.Replace(trHtml, modifiedTr);
            }
        }

        // If there are no tr elements within the table, add one
        if (!trRegex.IsMatch(tableHtml))
        {
            string newTr = "<tr><td></td></tr>";
            string modifiedTable = tableHtml.Insert(tableHtml.Length - 8, newTr); // Insert new tr before the closing </table> tag
            htmlData = htmlData.Replace(tableHtml, modifiedTable);
        }
    }

    return htmlData;
}

Thanks

Answer 1

unfortunately regex is not up to parsing malformed html. if you are not up to writing a parser and need to use c#, the HTML Agility Pack is your best bet.

https://html-agility-pack.net

you would parse the html, then walk the tree. you can detect text nodes as a children of a <TR> and convert to a <td>. if you find text node as child or <table> then you know to convert to <tr><td><text node>. same for <td> as table child.