using System;
using System.Collections.Generic;
using System.Text;
using System.Web;
using Microsoft.SharePoint;
using System.IO;
using Microsoft.SharePoint.Utilities;

namespace SharePointProducts.ActionRedirect
{
  public class RedirectHandler : IHttpHandler
  {
    public bool IsReusable
    {
      get { return true; }
    }

    public void ProcessRequest(HttpContext context)
    {
      HttpRequest request = context.Request;
      string url = request.QueryString["url"];
      if (!String.IsNullOrEmpty(url))
      {
        Redirect(context, url);
      }
    }

    private void Redirect(HttpContext context, string url)
    {
      SPSite site = null;
      SPWeb web = null;
      SPList list = null;
      SPListItem item = null;

      try
      {
        // Find list item from URL
        Uri uri = new Uri(url);
        site = new SPSite(url);
        site.CatchAccessDeniedException = false;
        web = site.OpenWeb();
        item = web.GetListItem(uri.PathAndQuery);
        list = item.ParentList;

        // Assemble server relative redirect URL
        string defaultViewUrl = list.DefaultViewUrl;
        int filenameIndex = defaultViewUrl.LastIndexOf('/');
        string formUrl = defaultViewUrl.Substring(0, filenameIndex + 1);
        formUrl += "DispForm.aspx?ID=" + item.ID;

        // Add RootFolder parameter to the redirect URL
        string folderUrl = web.ServerRelativeUrl;
        if (!folderUrl.EndsWith("/")) folderUrl += "/";
        folderUrl += item.Url;
        filenameIndex = folderUrl.LastIndexOf('/');
        folderUrl = folderUrl.Substring(0, filenameIndex);
        formUrl += "&RootFolder=" + SPEncode.UrlEncode(folderUrl);

        // Add Source parameter to the redirect URL
        string sourceUrl = uri.GetLeftPart(UriPartial.Authority);
        sourceUrl += folderUrl; 
        formUrl += "&Source=" + SPEncode.UrlEncode(sourceUrl);

        // Convert the server relative redirect URL to an absolute URL
        string newUrl = uri.GetLeftPart(UriPartial.Authority);
        newUrl += formUrl;

        context.Response.Redirect(newUrl, true);
      }

      finally
      {
        if (web != null) web.Dispose();
        if (site != null) site.Dispose();
      }
    }
  }
}