CacheDecorator.cs

namespace dotless.Core
{
    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Security.Cryptography;
    using System.Text;
    using Cache;
    using Loggers;

    public class CacheDecorator : ILessEngine
    {
        public readonly ILessEngine Underlying;
        public readonly ICache Cache;
        public ILogger Logger { get; set; }

        public CacheDecorator(ILessEngine underlying, ICache cache) : this(underlying, cache, NullLogger.Instance)
        {}

        public CacheDecorator(ILessEngine underlying, ICache cache, ILogger logger)
        {
            Underlying = underlying;
            Cache = cache;
            Logger = logger;
        }

        public string TransformToCss(string source, string fileName)
        {
            //Compute Cache Key
            var hash = ComputeContentHash(source);
            var cacheKey = fileName + hash;
            if (!Cache.Exists(cacheKey))
            {
                Logger.Debug(String.Format("Inserting cache entry for {0}", cacheKey));

                var css = Underlying.TransformToCss(source, fileName);
                var dependancies = new[] { fileName }.Concat(GetImports());
                
                Cache.Insert(cacheKey, dependancies, css);
                
                return css;
            }
            Logger.Debug(String.Format("Retrieving cache entry {0}", cacheKey));
            return Cache.Retrieve(cacheKey);
        }

        private string ComputeContentHash(string source)
        {
            SHA1 sha1 = SHA1.Create();
            byte[] computeHash = sha1.ComputeHash(Encoding.Default.GetBytes(source));
            return Convert.ToBase64String(computeHash);
        }

        public IEnumerable<string> GetImports()
        {
            return Underlying.GetImports();
        }

        public void ResetImports()
        {
            Underlying.ResetImports();
        }

        public bool LastTransformationSuccessful
        {
            get
            {
                return Underlying.LastTransformationSuccessful;
            }
        }
    }
}