Custom Renderer to Extend SmartTarget indexing metadata to include Keyword Key

Example.SmartTarget.Renderer.cs

using System;
using System.Xml;
using Tridion.ContentManager.CommunicationManagement;
using Tridion.ContentManager.ContentManagement;
using Tridion.ContentManager.Publishing;
using Tridion.ContentManager.Publishing.Rendering;
using Tridion.ContentManager.Publishing.Resolving;

namespace Example.SmartTarget
{
    /// <summary>
    /// Custom Renderer to extend SmartTarget publishing metadata to add a new index field for each keyword field
    /// which contains the keyword Key.
    /// </summary>
    public class Renderer : IRenderer
    {
        private const String KEY_SUFFIX = "_key";
        public void Render(ResolvedItem resolvedItem, PublishInstruction instruction, PublicationTarget target, RenderedItem renderedItem, RenderContext renderContext)
        {
            if (resolvedItem.IsDynamicComponentPresentation && renderedItem.Metadata!=null)
            {
                var metas = renderedItem.Metadata;
                for (int i=0; i< metas.Count;i++)
                {
                    if (metas[i].Name == "SmartTarget")
                    {
                        //Find all keywords on all the DCPs
                        foreach (XmlElement node in metas[i].SelectNodes("Component/Keyword"))
                        {
                            Keyword keyword = (Keyword)target.Session.GetObject(node.GetAttribute("id"));
                            if (keyword!=null && !String.IsNullOrEmpty(keyword.Key))
                            {
                                var componentRoot = node.ParentNode.SelectSingleNode("Source/*");
                                foreach (XmlElement field in GetKeywordFields(componentRoot, keyword))
                                {
                                    var keyNode = field.OwnerDocument.CreateElement(field.Name + KEY_SUFFIX, field.NamespaceURI);
                                    keyNode.InnerText = keyword.Key;
                                    field.ParentNode.InsertAfter(keyNode, field);
                                }
                            }
                        }
                    }
                }                
            }
        }

        /// <summary>
        /// Gets the fields in component XML that have a certain keyword value.
        /// Note that this is a rather simple method that does matching based on
        /// The keyword Title. If you happen to have non-keyword text fields with
        /// the same value, or keywords in different categories with the same value
        /// you might get unexpected results
        /// </summary>
        /// <param name="componentRoot">component XML</param>
        /// <param name="keyword">keyword to look for</param>
        /// <returns>list of field elements</returns>
        protected XmlNodeList GetKeywordFields(XmlNode componentRoot, Keyword keyword)
        {
            var title = keyword.Title;
            var delimiter = "'";
            if (title.Contains("'"))
            {
                if (title.Contains("\""))
                {
                    //If title contains both double and single quotes we skip it, as its tricky to select these elements using XPath
                    return null;
                }
                delimiter = "\"";
            }
            var xpath= String.Format("//*[text()={1}{0}{1}]",keyword.Title, delimiter);
            return componentRoot.SelectNodes(xpath);
        }
    }
}