Asset.cs

using System;
using System.IO;
using System.Linq;
using System.Security.Cryptography;
using System.Web.Hosting;
using Path = Fluent.IO.Path;

namespace WebCache
{
	public class Asset
	{
		internal static readonly string CacheFolderName = "webcache";

		public string OriginalVirtualPath { get; private set; }
		public string CachedVirtualPath { get; private set; }
		public Path File { get; private set; }

		public Asset(string virtualPath)
		{
			OriginalVirtualPath = virtualPath;
			var originalFilePath = HostingEnvironment.MapPath(virtualPath);
			var originalFile = GetFile(originalFilePath);
			var hash = GetHash(originalFile);
			File = CreateFile(originalFile, hash);
			CachedVirtualPath = string.Format("{0}/{1}", virtualPath.Substring(0, virtualPath.LastIndexOf("/", StringComparison.Ordinal)), File.FileName);
		}
		
		private Path CreateFile(Path file, string hash)
		{
			var applicationRoot = HostingEnvironment.ApplicationPhysicalPath;
			var relativePath = file
				.DirectoryName
				.Split(new [] { applicationRoot }, 2, StringSplitOptions.None)
				.Last();
			var newFileName = string.Format("{0}.{1}.webcache{2}", file.FileNameWithoutExtension, hash, file.Extension);
			var newFilePath = Path.Get(applicationRoot, CacheFolderName, relativePath, newFileName);

			Path newFile;
			try
			{
				newFile = file.Copy(newFilePath);
			}
			catch (Exception exception)
			{
				throw new IOException("Could not copy file to: " + newFilePath.FullPath, exception);
			}

			return newFile;
		}

		private Path GetFile(string path)
		{
			var file = Path.Get(path);

			if (!file.Exists)
				throw new FileNotFoundException("Could not find file to cache: " + path);

			return file;
		}

		private string GetHash(Path file)
		{
			byte[] bytes;

			using (var md5 = MD5.Create())
			using (var stream = System.IO.File.OpenRead(file.FullPath))
				bytes = md5.ComputeHash(stream);

			return BitConverter
				.ToString(bytes)
				.Replace("-", string.Empty)
				.ToLower();
		}
	}
}