FubuMVC asset pipeline transformer that finds and replaces an InputModel place holder with its route URL. Helpful in avoiding hard-coding an AJAX URL in your JavaScript asset files (though any asset file type will be feed through this transformer).

UrlTransformationException.cs

using System;
using System.Collections.Generic;
using System.Text;
using FubuMVC.Core.Assets.Files;

namespace Some.Namespace.Here
{
    public class UrlTransformationException : Exception
    {
        string _message;

        public UrlTransformationException(string message)
            : base(message)
        {
        }

        public UrlTransformationException(string contents, IEnumerable<AssetFile> files)
        {
            var message = new StringBuilder("A url was not resolved");
            foreach (var assetFile in files)
            {
                message.AppendFormat("File: {0}", assetFile.Name);
                message.AppendLine();
            }

            _message = message.ToString();
        }

        public override string Message
        {
            get { return _message; }
        }
    }
}

UrlTransformer.cs

using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;
using FubuCore;
using FubuMVC.Core.Assets.Content;
using FubuMVC.Core.Assets.Files;

namespace Some.Namespace.Here
{
    public class UrlTransformer : ITransformer
    {
        readonly IModelUrlResolver _urlResolver;

        public UrlTransformer(IModelUrlResolver urlResolver)
        {
            _urlResolver = urlResolver;
        }

        public string Transform(string contents, IEnumerable<AssetFile> files)
        {
            var regex = new Regex(@"url::(?<InputModel>[A-Za-z\.]+)");
            var matches = regex.Matches(contents);
            var replacements = findReplacements(matches).Distinct();
            var replacedContents = contents;
            replacements.Each(r =>
            {
                var url = _urlResolver.GetUrlForInputModelName(r);

                var alteredUrl = @"url::{0}".ToFormat(r);
                replacedContents = replacedContents.Replace(alteredUrl, url);
            });

            if (replacedContents.Contains("url::"))
                throw new UrlTransformationException(contents, files);

            return replacedContents;
        }

        private IEnumerable<string> findReplacements(MatchCollection matchCollection)
        {
            return from Match match in matchCollection select match.Groups["InputModel"].Value;
        }
    }
}

It looks like a better sample is over at Corey Kaylor's gist: https://gist.github.com/1563424