Minify HTML with inline css/javascript for MVC C# as a ActionFilterAttribute

MinifyHtmlAttribute.cs

using System;
using System.IO;
using System.Linq;
using System.Text;
using System.Web;
using System.Web.Mvc;
using System.Web.Optimization;
using ZetaProducerHtmlCompressor.Internal;

namespace PmdWebsite.Helpers.ActionFilters
{
    public sealed class MinifyHtmlAttribute : ActionFilterAttribute
    {
        public override void OnActionExecuting(
          ActionExecutingContext filterContext)
        {
            var response = filterContext.HttpContext.Response;

            if (response.Filter == null) return;

            HtmlCompressor compressor = new HtmlCompressor();
            ResponseFilterStream filter = new ResponseFilterStream(response.Filter);
            compressor.setRemoveComments(true);
            compressor.setCssCompressor(new CssCompressor(filterContext.HttpContext));
            compressor.setCompressCss(true);
            compressor.setJavaScriptCompressor(new JsCompressor(filterContext.HttpContext));
            compressor.setCompressJavaScript(true);
            filter.TransformString += s =>
            {
                return compressor.compress(s);
            };
            response.Filter = filter;
        }

        private class CssCompressor : ICompressor
        {
            HttpContextBase HttpContext { get; set; }
            public CssCompressor(HttpContextBase httpContext)
            {
                HttpContext = httpContext;
            }
            public string compress(string source)
            {
                var bundleContext = new BundleContext(HttpContext, BundleTable.Bundles, "~/css/inline");
                var bundle = BundleTable.Bundles.Single(b => b.Path == "~/css/inline");
                var bundleResponse = bundle.GenerateBundleResponse(bundleContext);
                bundleResponse.Content = source;
                bundleResponse.ContentType = "text/css";
                new CssMinify().Process(bundleContext, bundleResponse);
                if (bundleResponse.Content.Contains("Minification failed"))
                {
                    return source;
                }
                return bundleResponse.Content;
            }
        }

        private class JsCompressor : ICompressor
        {
            HttpContextBase HttpContext { get; set; }
            public JsCompressor(HttpContextBase httpContext)
            {
                HttpContext = httpContext;
            }
            public string compress(string source)
            {
                var bundleContext = new BundleContext(HttpContext, BundleTable.Bundles, "~/script/inline");
                var bundle = BundleTable.Bundles.Single(b => b.Path == "~/script/inline");
                var bundleResponse = bundle.GenerateBundleResponse(bundleContext);
                bundleResponse.Content = source;
                bundleResponse.ContentType = "text/javascript";
                new JsMinify().Process(bundleContext, bundleResponse);
                if (bundleResponse.Content.Contains("Minification failed"))
                {
                    return source;
                }
                return bundleResponse.Content;
            }
        }
        /// <summary>
        /// A semi-generic Stream implementation for Response.Filter with
        /// an event interface for handling Content transformations via
        /// Stream or String.    
        /// <remarks>
        /// Use with care for large output as this implementation copies
        /// the output into a memory stream and so increases memory usage.
        /// </remarks>
        /// </summary>    
        private class ResponseFilterStream : Stream
        {
            /// <summary>
            /// The original stream
            /// </summary>
            Stream _stream;

            /// <summary>
            /// Current position in the original stream
            /// </summary>
            long _position;

            /// <summary>
            /// Stream that original content is read into
            /// and then passed to TransformStream function
            /// </summary>
            MemoryStream _cacheStream = new MemoryStream(5000);

            /// <summary>
            /// Internal pointer that that keeps track of the size
            /// of the cacheStream
            /// </summary>
            int _cachePointer = 0;


            /// <summary>
            /// 
            /// </summary>
            /// <param name="responseStream"></param>
            public ResponseFilterStream(Stream responseStream)
            {
                _stream = responseStream;
            }


            /// <summary>
            /// Determines whether the stream is captured
            /// </summary>
            private bool IsCaptured
            {
                get
                {

                    if (CaptureStream != null || CaptureString != null ||
                        TransformStream != null || TransformString != null)
                        return true;

                    return false;
                }
            }

            /// <summary>
            /// Determines whether the Write method is outputting data immediately
            /// or delaying output until Flush() is fired.
            /// </summary>
            private bool IsOutputDelayed
            {
                get
                {
                    if (TransformStream != null || TransformString != null)
                        return true;

                    return false;
                }
            }


            /// <summary>
            /// Event that captures Response output and makes it available
            /// as a MemoryStream instance. Output is captured but won't 
            /// affect Response output.
            /// </summary>
            public event Action<MemoryStream> CaptureStream;

            /// <summary>
            /// Event that captures Response output and makes it available
            /// as a string. Output is captured but won't affect Response output.
            /// </summary>
            public event Action<string> CaptureString;



            /// <summary>
            /// Event that allows you transform the stream as each chunk of
            /// the output is written in the Write() operation of the stream.
            /// This means that that it's possible/likely that the input 
            /// buffer will not contain the full response output but only
            /// one of potentially many chunks.
            /// 
            /// This event is called as part of the filter stream's Write() 
            /// operation.
            /// </summary>
            public event Func<byte[], byte[]> TransformWrite;


            /// <summary>
            /// Event that allows you to transform the response stream as
            /// each chunk of bytep[] output is written during the stream's write
            /// operation. This means it's possibly/likely that the string
            /// passed to the handler only contains a portion of the full
            /// output. Typical buffer chunks are around 16k a piece.
            /// 
            /// This event is called as part of the stream's Write operation.
            /// </summary>
            public event Func<string, string> TransformWriteString;

            /// <summary>
            /// This event allows capturing and transformation of the entire 
            /// output stream by caching all write operations and delaying final
            /// response output until Flush() is called on the stream.
            /// </summary>
            public event Func<MemoryStream, MemoryStream> TransformStream;

            /// <summary>
            /// Event that can be hooked up to handle Response.Filter
            /// Transformation. Passed a string that you can modify and
            /// return back as a return value. The modified content
            /// will become the final output.
            /// </summary>
            public event Func<string, string> TransformString;


            protected virtual void OnCaptureStream(MemoryStream ms)
            {
                if (CaptureStream != null)
                    CaptureStream(ms);
            }


            private void OnCaptureStringInternal(MemoryStream ms)
            {
                if (CaptureString != null)
                {
                    string content = HttpContext.Current.Response.ContentEncoding.GetString(ms.ToArray());
                    OnCaptureString(content);
                }
            }

            protected virtual void OnCaptureString(string output)
            {
                if (CaptureString != null)
                    CaptureString(output);
            }

            protected virtual byte[] OnTransformWrite(byte[] buffer)
            {
                if (TransformWrite != null)
                    return TransformWrite(buffer);
                return buffer;
            }

            private byte[] OnTransformWriteStringInternal(byte[] buffer)
            {
                Encoding encoding = HttpContext.Current.Response.ContentEncoding;
                string output = OnTransformWriteString(encoding.GetString(buffer));
                return encoding.GetBytes(output);
            }

            private string OnTransformWriteString(string value)
            {
                if (TransformWriteString != null)
                    return TransformWriteString(value);
                return value;
            }


            protected virtual MemoryStream OnTransformCompleteStream(MemoryStream ms)
            {
                if (TransformStream != null)
                    return TransformStream(ms);

                return ms;
            }




            /// <summary>
            /// Allows transforming of strings
            /// 
            /// Note this handler is internal and not meant to be overridden
            /// as the TransformString Event has to be hooked up in order
            /// for this handler to even fire to avoid the overhead of string
            /// conversion on every pass through.
            /// </summary>
            /// <param name="responseText"></param>
            /// <returns></returns>
            private string OnTransformCompleteString(string responseText)
            {
                if (TransformString != null)
                    TransformString(responseText);

                return responseText;
            }

            /// <summary>
            /// Wrapper method form OnTransformString that handles
            /// stream to string and vice versa conversions
            /// </summary>
            /// <param name="ms"></param>
            /// <returns></returns>
            internal MemoryStream OnTransformCompleteStringInternal(MemoryStream ms)
            {
                if (TransformString == null)
                    return ms;

                //string content = ms.GetAsString();
                string content = HttpContext.Current.Response.ContentEncoding.GetString(ms.ToArray());

                content = TransformString(content);
                byte[] buffer = HttpContext.Current.Response.ContentEncoding.GetBytes(content);
                ms = new MemoryStream();
                ms.Write(buffer, 0, buffer.Length);
                //ms.WriteString(content);

                return ms;
            }

            /// <summary>
            /// 
            /// </summary>
            public override bool CanRead
            {
                get { return true; }
            }

            public override bool CanSeek
            {
                get { return true; }
            }
            /// <summary>
            /// 
            /// </summary>
            public override bool CanWrite
            {
                get { return true; }
            }

            /// <summary>
            /// 
            /// </summary>
            public override long Length
            {
                get { return 0; }
            }

            /// <summary>
            /// 
            /// </summary>
            public override long Position
            {
                get { return _position; }
                set { _position = value; }
            }

            /// <summary>
            /// 
            /// </summary>
            /// <param name="offset"></param>
            /// <param name="direction"></param>
            /// <returns></returns>
            public override long Seek(long offset, System.IO.SeekOrigin direction)
            {
                return _stream.Seek(offset, direction);
            }

            /// <summary>
            /// 
            /// </summary>
            /// <param name="length"></param>
            public override void SetLength(long length)
            {
                _stream.SetLength(length);
            }

            /// <summary>
            /// 
            /// </summary>
            public override void Close()
            {
                _stream.Close();
            }

            /// <summary>
            /// Override flush by writing out the cached stream data
            /// </summary>
            public override void Flush()
            {

                if (IsCaptured && _cacheStream.Length > 0)
                {
                    // Check for transform implementations
                    _cacheStream = OnTransformCompleteStream(_cacheStream);
                    _cacheStream = OnTransformCompleteStringInternal(_cacheStream);

                    OnCaptureStream(_cacheStream);
                    OnCaptureStringInternal(_cacheStream);

                    // write the stream back out if output was delayed
                    if (IsOutputDelayed)
                        _stream.Write(_cacheStream.ToArray(), 0, (int)_cacheStream.Length);

                    // Clear the cache once we've written it out
                    _cacheStream.SetLength(0);
                }

                // default flush behavior
                _stream.Flush();
            }

            /// <summary>
            /// 
            /// </summary>
            /// <param name="buffer"></param>
            /// <param name="offset"></param>
            /// <param name="count"></param>
            /// <returns></returns>
            public override int Read(byte[] buffer, int offset, int count)
            {
                return _stream.Read(buffer, offset, count);
            }


            /// <summary>
            /// Overriden to capture output written by ASP.NET and captured
            /// into a cached stream that is written out later when Flush()
            /// is called.
            /// </summary>
            /// <param name="buffer"></param>
            /// <param name="offset"></param>
            /// <param name="count"></param>
            public override void Write(byte[] buffer, int offset, int count)
            {
                if (IsCaptured)
                {
                    // copy to holding buffer only - we'll write out later
                    _cacheStream.Write(buffer, 0, count);
                    _cachePointer += count;
                }

                // just transform this buffer
                if (TransformWrite != null)
                    buffer = OnTransformWrite(buffer);
                if (TransformWriteString != null)
                    buffer = OnTransformWriteStringInternal(buffer);

                if (!IsOutputDelayed)
                    _stream.Write(buffer, offset, buffer.Length);

            }

        }
    }
}

Using ZetaProducerHtmlCompressor
Ispired by Marius Schulz - Inlining CSS and JavaScript Bundles with ASP.NET MVC
Cause Minify Resources (HTML, CSS, and JavaScript)
ResponseFilterStream from Rick Strahl's - Capturing and Transforming ASP.NET Output with Response.Filter

In your BundleConfig.cs:
/*These "inline" bundles are required for HTML minification*/ bundles.Add(new StyleBundle("~/css/inline").Include( "~/Content/css/Styles/critical/inline.css")); bundles.Add(new ScriptBundle("~/script/inline").Include( "~/Scripts/minify/inline.js")); these files can be empty.

Use as a [Attribute] on a Action, Controller or in you FilterConfig.cs as:
filters.Add(new MinifyHtmlAttribute());