ASP.NET and jQuery to the Max

//--------------------------------------------------------------------------------------------------------------
// Created by		: Gianluca Negrelli
// Copyright		: 2010.05.15  
//--------------------------------------------------------------------------------------------------------------

using System;
using System.Collections.Generic;
using System.IO;
using System.Security.Cryptography;
using System.Web;
using System.Web.Caching;
using System.Web.UI;

namespace EcommerceWebSite.Controls
{
	/// <summary>
	/// Base class for web site pages.
	/// </summary>
	public abstract class BasePage : Page
	{
		#region ClientVariables

		/// <summary>
		/// Label collection that is rendered to the client.
		/// </summary>
		private Dictionary<string, object> ScriptVariables = new Dictionary<string, object>();

		/// <summary>
		/// Prerender event.
		/// </summary>
		protected override void OnPreRender(System.EventArgs e)
		{
			if (ScriptVariables.Count > 0)
			{
				ClientVariableRenderer cv = new ClientVariableRenderer();
				foreach (KeyValuePair<string, object> currKey in ScriptVariables)
				{
					cv.Add(currKey.Key, currKey.Value);
				}
			}
			base.OnPreRender(e);
		}

		/// <summary>
		/// Method to add object to script variable collection.
		/// </summary>
		public void AddClientVariable(string name, object value)
		{
			ScriptVariables.Add(name, value);
		}

		#endregion Client Variables

		#region Version javascript

		private static readonly string cacheFile;
		private static object lockerExternalFile = new object();

		/// <summary>
		/// Resolves url and adds a query string with the file hash.
		/// The hash is stored into a cache depending on a file.
		/// </summary>
		public string ResolveAndVersionUrl(string url)
		{
			url = this.ResolveUrl(url);
			string fileName = this.Server.MapPath(url);
			lock (lockerExternalFile)
			{
				// Verifies if the file hash is already in cache
				object o = HttpContext.Current.Cache["BaseMasterPage::" + fileName];
				if (o == null)
				{
					// Check if file exists or not
					if (!File.Exists(fileName))
					{
						throw new Exception("The file " + url + " doesn't exist");
					}

					// Calculates the hash
					o = GetMD5HashFromFile(fileName);

					// Verifies if cache tracking file exists
					CheckFileCache();

					CacheDependency d = new CacheDependency(cacheFile);
					HttpContext.Current.Cache.Insert("BasePage::" + fileName, o, d, DateTime.Now.AddDays(1), Cache.NoSlidingExpiration);
				}
				return string.Format("{0}?{1}", url, o);
			}
		}

		/// <summary>
		/// Gets the hash of the file.
		/// </summary>
		private string GetMD5HashFromFile(string fileName)
		{
			byte[] retVal = null;
			using (FileStream file = new FileStream(fileName, FileMode.Open))
			{
				using (MD5 md5 = MD5CryptoServiceProvider.Create())
				{
					retVal = md5.ComputeHash(file);
				}
				file.Close();
			}
			return Convert.ToBase64String(retVal);
		}

		/// <summary>
		/// Checks if cache tracking file exists otherwise it creates it.
		/// </summary>
		private void CheckFileCache()
		{
			if (!File.Exists(cacheFile))
			{
				using (FileStream fs = new FileStream(cacheFile, FileMode.Create, FileAccess.Write))
				{
					fs.Close();
				}
			}
		}

		#endregion Version javascript

		#region Constructor 

		static BasePage()
		{
			cacheFile = HttpContext.Current.Server.MapPath(@"~/cache\CacheFile_JsFileVersioner");
			FileInfo cacheFolder = new FileInfo(cacheFile);
			if (!cacheFolder.Directory.Exists) 
			{
				throw new Exception("Cache folder doesn't exist.");
			}
		}

		#endregion
	}
}