Basic srcset generator for ImageProcessor in Umbraco v8

ResponsiveImageHelper.cs

using System.Collections.Specialized;
using System.Globalization;
using System.Linq;
using System.Text;
using System.Web;

namespace MooseCoding.Web.UI
{
    public static class ResponsiveImageHelper
    {
        // TODO: These will need to be optimised for the site's images, ideally based on real-world user/device data.
        public static int[] Widths = { 320, 480, 640, 768, 1024, 1366, 1600, 1920, 2560, 3840 };

        /// <summary>
        /// Turn a crop URL into a srcset of multiple sizes for responsive image loading. 
        /// </summary>
        /// <param name="cropUrl">The image URL, probably generated with <seealso cref="Umbraco.Web.ImageCropperTemplateExtensions.GetCropUrl"/></param>
        /// <param name="maxWidth">Will not return image URLs larger than this, not strictly necessary but will cut down on HTML and cache use, if you set this remember to account for high-DPI!</param>
        /// <returns></returns>
        public static string GetSrcSet(string cropUrl, uint? maxWidth = null)
        {
            maxWidth = maxWidth ?? uint.MaxValue;

            uint? height = null;

            var urlParts = cropUrl.Split('?');

            var queryParams = urlParts.Length == 2 ? HttpUtility.ParseQueryString(urlParts[1]) : new NameValueCollection();

            _ = uint.TryParse(queryParams.Get("width"), out uint width);

            if (uint.TryParse(queryParams.Get("height"), out uint parsedHeight))
            {
                height = parsedHeight;
            }

            if (decimal.TryParse(queryParams.Get("heightratio"), out decimal heightRatio))
            {
                height = (uint)(heightRatio * width);
            }

            // remove any predetermined sizes, we're going to recalculate
            queryParams.Remove("width");
            queryParams.Remove("height");
            queryParams.Remove("heightratio");

            var sb = new StringBuilder();

            foreach (var w in Widths.Where(w => w < maxWidth))
            {
                sb.Append($"{urlParts[0]}?width={w}");

                // If there's a height defined, crop to an aspect ratio.
                // unless there's a crop set, as ImageProcessor will then determine the height as a %age of width
                if (height.HasValue && queryParams.Get("crop") == null)
                {
                    sb.AppendFormat(CultureInfo.InvariantCulture, "&heightratio={0}", height / (decimal)width);
                }

                // re-apply all other params
                if (queryParams.Count > 0)
                {
                    sb.Append($"&{queryParams}");
                }

                sb.Append($" {w}w, ");
            }

            sb.Remove(sb.Length - 2, 2);

            return sb.ToString();
        }
    }
}