Umbraco-CMS/src/Umbraco.Web/Templates/HtmlImageSourceParser.cs

using System.Collections.Generic;
using System.Text.RegularExpressions;
using Umbraco.Core;

namespace Umbraco.Web.Templates
{

    public sealed class HtmlImageSourceParser
    {
        public HtmlImageSourceParser(IUmbracoContextAccessor umbracoContextAccessor)
        {
            _umbracoContextAccessor = umbracoContextAccessor;
        }

        private static readonly Regex ResolveImgPattern = new Regex(@"(<img[^>]*src="")([^""\?]*)([^""]*""[^>]*data-udi="")([^""]*)(""[^>]*>)",
            RegexOptions.Compiled | RegexOptions.IgnoreCase | RegexOptions.IgnorePatternWhitespace);
        private readonly IUmbracoContextAccessor _umbracoContextAccessor;        

        private static readonly Regex DataUdiAttributeRegex = new Regex(@"data-udi=\\?(?:""|')(?<udi>umb://[A-z0-9\-]+/[A-z0-9]+)\\?(?:""|')",
            RegexOptions.Compiled | RegexOptions.CultureInvariant | RegexOptions.IgnoreCase);

        /// <summary>
        /// Parses out UDIs from an html string based on 'data-udi' html attributes
        /// </summary>
        /// <param name="text"></param>
        /// <returns></returns>
        public IEnumerable<Udi> FindUdisFromDataAttributes(string text)
        {
            var matches = DataUdiAttributeRegex.Matches(text);
            if (matches.Count == 0)
                yield break;

            foreach (Match match in matches)
            {
                if (match.Groups.Count == 2 && Udi.TryParse(match.Groups[1].Value, out var udi))
                    yield return udi;
            }
        }

        /// <summary>
        /// Parses the string looking for Umbraco image tags and updates them to their up-to-date image sources.
        /// </summary>
        /// <param name="text"></param>
        /// <returns></returns>
        /// <remarks>Umbraco image tags are identified by their data-udi attributes</remarks>
        public string EnsureImageSources(string text)
        {
            // don't attempt to proceed without a context
            if (_umbracoContextAccessor?.UmbracoContext?.UrlProvider == null)
            {
                return text;
            }

            var urlProvider = _umbracoContextAccessor.UmbracoContext.UrlProvider;

            return ResolveImgPattern.Replace(text, match =>
            {
                // match groups:
                // - 1 = from the beginning of the image tag until src attribute value begins
                // - 2 = the src attribute value excluding the querystring (if present)
                // - 3 = anything after group 2 and before the data-udi attribute value begins
                // - 4 = the data-udi attribute value
                // - 5 = anything after group 4 until the image tag is closed
                var udi = match.Groups[4].Value;
                if (udi.IsNullOrWhiteSpace() || GuidUdi.TryParse(udi, out var guidUdi) == false)
                {
                    return match.Value;
                }
                var mediaUrl = urlProvider.GetMediaUrl(guidUdi.Guid);
                if (mediaUrl == null)
                {
                    // image does not exist - we could choose to remove the image entirely here (return empty string),
                    // but that would leave the editors completely in the dark as to why the image doesn't show
                    return match.Value;
                }

                return $"{match.Groups[1].Value}{mediaUrl}{match.Groups[3].Value}{udi}{match.Groups[5].Value}";
            });
        }

        /// <summary>
        /// Removes media urls from &lt;img&gt; tags where a data-udi attribute is present
        /// </summary>
        /// <param name="text"></param>
        /// <returns></returns>
        public string RemoveImageSources(string text)
            // see comment in ResolveMediaFromTextString for group reference
            => ResolveImgPattern.Replace(text, "$1$3$4$5");

        
    }
}