using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Reflection;
using System.Web.Mvc;
using System.IO;
using System.Web.UI;
using System.Web.Caching;
using System.Text;

namespace Uploading.Actions
{
    public class ActionOutputCacheAttribute : ActionFilterAttribute
    {
        // This hack is optional; I'll explain it later in the blog post
        private static MethodInfo _switchWriterMethod = typeof(HttpResponse).GetMethod("SwitchWriter", BindingFlags.Instance | BindingFlags.NonPublic);

        public ActionOutputCacheAttribute(int cacheDuration)
        {
            _cacheDuration = cacheDuration;
        }

        private int _cacheDuration;
        private TextWriter _originalWriter;
        private string _cacheKey;

        public override void OnActionExecuting(ActionExecutingContext filterContext)
        {
            _cacheKey = ComputeCacheKey(filterContext);
            CacheContainer cachedOutput = (CacheContainer)filterContext.HttpContext.Cache[_cacheKey];
            if (cachedOutput != null)
            {
                filterContext.HttpContext.Response.ContentType = cachedOutput.ContentType;
                filterContext.Result = new ContentResult { Content = cachedOutput.Output };
            }
            else
            {
                StringWriter stringWriter = new StringWriterWithEncoding(filterContext.HttpContext.Response.ContentEncoding);
                HtmlTextWriter newWriter = new HtmlTextWriter(stringWriter);
                _originalWriter = (TextWriter)_switchWriterMethod.Invoke(HttpContext.Current.Response, new object[] { newWriter });
            }
        }

        public override void OnResultExecuted(ResultExecutedContext filterContext)
        {
            if (_originalWriter != null) // Must complete the caching
            {
                HtmlTextWriter cacheWriter = (HtmlTextWriter)_switchWriterMethod.Invoke(HttpContext.Current.Response, new object[] { _originalWriter });
                string textWritten = ((StringWriter)cacheWriter.InnerWriter).ToString();
                filterContext.HttpContext.Response.Write(textWritten);
                CacheContainer container = new CacheContainer(textWritten, filterContext.HttpContext.Response.ContentType);
                filterContext.HttpContext.Cache.Add(_cacheKey, container, null, DateTime.Now.AddSeconds(_cacheDuration), Cache.NoSlidingExpiration, System.Web.Caching.CacheItemPriority.Normal, null);
            }
        }

        private string ComputeCacheKey(ActionExecutingContext filterContext)
        {
            var keyBuilder = new StringBuilder();
            foreach (var pair in filterContext.RouteData.Values)
                keyBuilder.AppendFormat("rd{0}_{1}_", pair.Key.GetHashCode(), pair.Value.GetHashCode());
            foreach (var pair in filterContext.ActionParameters)
                keyBuilder.AppendFormat("ap{0}_{1}_", pair.Key.GetHashCode(), pair.Value.GetHashCode());
            return keyBuilder.ToString();
        }
    }

    class CacheContainer
    {
        public string Output;
        public string ContentType;

        /// <summary>
        /// Initializes a new instance of the CacheContainer class.
        /// </summary>
        /// <param name="data"></param>
        /// <param name="contentType"></param>
        public CacheContainer(string data, string contentType)
        {
            Output = data;
            ContentType = contentType;
        }
    }
}