Bloom.Book.BookStorage.CleanupUnusedImageFiles C# (CSharp) Method

        public void CleanupUnusedImageFiles()
        {
            //Collect up all the image files in our book's directory
            var imageFiles = new List<string>();
            var imageExtentions = new HashSet<string>(new []{ ".jpg", ".png", ".svg" });
            var ignoredFilenameStarts = new HashSet<string>(new [] { "thumbnail", "placeholder", "license" });
            foreach (var path in Directory.EnumerateFiles(this._folderPath).Where(
                s => imageExtentions.Contains(Path.GetExtension(s).ToLowerInvariant())))
            {
                var filename = Path.GetFileName(path);
                if (ignoredFilenameStarts.Any(s=>filename.StartsWith(s, StringComparison.InvariantCultureIgnoreCase)))
                    continue;
                imageFiles.Add(Path.GetFileName(GetNormalizedPathForOS(path)));
            }
            //Remove from that list each image actually in use
            var element = Dom.RawDom.DocumentElement;
            var toRemove = GetImagePathsRelativeToBook(element);

            //also, remove from the doomed list anything referenced in the datadiv that looks like an image
            //This saves us from deleting, for example, cover page images if this is called before the front-matter
            //has been applied to the document.
            toRemove.AddRange(from XmlElement dataDivImage in Dom.RawDom.SelectNodes("//div[@id='bloomDataDiv']//div[contains(text(),'.png') or contains(text(),'.jpg') or contains(text(),'.svg')]")
                              select UrlPathString.CreateFromUrlEncodedString(dataDivImage.InnerText.Trim()).PathOnly.NotEncoded);
            foreach (var fileName in toRemove)
            {
                imageFiles.Remove(GetNormalizedPathForOS(fileName));   //Remove just returns false if it's not in there, which is fine
            }

            //Delete any files still in the list
            foreach (var fileName in imageFiles)
            {
                var path = Path.Combine(_folderPath, fileName);
                try
                {
                    Debug.WriteLine("Removed unused image: "+path);
                    Logger.WriteEvent("Removed unused image: " + path);
                    RobustFile.Delete(path);
                }
                catch (Exception)
                {
                    Debug.WriteLine("Could not remove unused image: " + path);
                    Logger.WriteEvent("Could not remove unused  image: " + path);
                    //It's not worth bothering the user about, we'll get it someday.
                    //We're not even doing a Debug.Fail because that makes it harder to unit test this condition.
                }
            }
        }