Replace html image urls with the cid of the attachments

ConvertHtmlSrcToAttachmentCid.cs

        
var templateDecoded = Encoding.UTF8.GetString(Convert.FromBase64String(campaign.Template));
templateDecoded = ReplaceHtmlImagesWithCIds(templateDecoded);
        
private string[] GetImageNamesFromHtml(string html)
{
    string[] htmlImgSrcNames = Regex.Matches(html, @"<img.+?src=[\""'](.*?[\\/])?(.+?)[\""'].*?>", RegexOptions.IgnoreCase).Select(x => x.Groups[2].Value).ToArray();
    string[] htmlImgUrlNames = Regex.Matches(html, @"url\([\""']?(.*?[\\/])(.+?)[\""']?\)", RegexOptions.IgnoreCase).Select(x => x.Groups[1].Value).ToArray();
    string[] htmlImageNames = htmlImgSrcNames.Concat(htmlImgUrlNames).Where(x => !string.IsNullOrEmpty(x)).Distinct().ToArray();

    return htmlImageNames;
}

private string ReplaceHtmlImagesWithCIds(string html)
{
    string[] htmlImageNames = GetImageNamesFromHtml(html);

    string result = html;

    foreach (var imageName in htmlImageNames)
    {
        result = result.Replace(imageName, $"cid:{imageName}");
    }

    return result;
}