Caching WCF javascript proxy on browser

#undef IIS6
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.IO;

namespace WcfService1
{
    public sealed class JavascriptProxyCacheModule : IHttpModule
    {
        private HttpApplication app;
                
        public void Init(HttpApplication context)
        {
            app = context;
            app.EndRequest += new EventHandler(app_EndRequest);
            app.BeginRequest += new EventHandler(app_BeginRequest);
        }

        void app_BeginRequest(object sender, EventArgs e)
        {
            var path = app.Context.Request.Path.ToLower().Replace('\\', '/');
            if (IsWcfJavacsriptProxy(path))
            {
                // versioning is used by using (xxx) in the path of the script
                // reference. for ex, /(v2)/Service.svc/js
                // In this case, remove the (v2)/ 
                int pos = path.IndexOf('(');
                if (pos > 0)
                {
                    int endPos = path.IndexOf(')');
                    path = path.Substring(0, pos) + path.Substring(endPos + 2);
                    app.Context.RewritePath(path);

                    string ifModifiedSince = app.Context.Request.Headers["If-Modified-Since"];
                    if (!string.IsNullOrEmpty(ifModifiedSince))
                    {
                        string filePath = app.Context.Request.PhysicalPath;
                        DateTime fileLastModifyDateTime = File.GetLastWriteTime(filePath);
                        DateTime browserLastModifyDateTime;
                        if (DateTime.TryParse(ifModifiedSince, out browserLastModifyDateTime))
                        {
                            if ((browserLastModifyDateTime - fileLastModifyDateTime).Seconds > 5)
                            {
                                app.Context.Response.StatusCode = 304;
                                app.Context.Response.End();
                            }
                        }
                    }
                }                
            }
        }

        private void app_EndRequest(object sender, EventArgs e)
        {
            var path = app.Context.Request.Path.ToLower().Replace('\\', '/');
            
            if (app.Context.Response.StatusCode == 200
                || app.Context.Response.StatusCode == 202)
            {
                if (IsWcfJavacsriptProxy(path) && IsVersioned())
                {
                    var lastModified = DateTime.UtcNow;
                    // Expire by tomorrow 7 AM always.
                    var expires = lastModified.AddDays(1).Subtract(lastModified.TimeOfDay).AddHours(7);
                    HttpCachePolicy cache = app.Context.Response.Cache;
                    cache.SetLastModified(lastModified);
                    cache.SetExpires(expires);
                    cache.SetCacheability(HttpCacheability.Public);
                }
            }            

        }

        private bool IsWcfJavacsriptProxy(string path)
        {
            // It has to be a .svc extension hit
            // And it must have the version number on the URL. Don't want to accidentally
            // cache non versioned WCF proxies.
            // Then it must have a /js or /jsdebug hit
            return path.Contains(".svc/") 
                && (path.EndsWith("/js") || path.EndsWith("/jsdebug"));
        }

        private bool IsVersioned()
        {
            return app.Context.Request.RawUrl.IndexOf('(') > 0;
        }

        public void Dispose()
        {            
#if IIS6
            app.EndRequest -= app_EndRequest;
            app.BeginRequest -= app_BeginRequest;            
#endif
            app = null;            
        }
    }
}