Option Strict Off
Option Explicit On

#Region " Imports "
Imports Nancy
Imports Nancy.Bootstrapper
Imports Nancy.TinyIoc
Imports System.IO
#End Region

''' <summary>
''' Override application start and add a method to minify HTML responses from Nancy, at the end of the pipeline.
''' Written by Thomas Williams at https://thomasswilliams.github.io, shared with CC BY 4 license. This bootstrapper
''' will be picked up by default by Nancy as per docs:
'''   "When the application starts up, Nancy looks for a custom bootstrapper. By default, it scans all assemblies
'''    with a reference to Nancy. If it doesn't find one, it'll fall back to the DefaultNancyBootstrapper."
''' </summary>
Public Class NancyBootstrapperEx
  Inherits DefaultNancyBootstrapper

  ''' <summary>
  ''' On application startup, add a handler after requests, to minify HTML content. Adapted from
  ''' http://simoncropp.com/httpcompressionwithnancyfx,
  ''' https://yobriefca.se/blog/2011/11/01/nancy-jsonp-hook/.
  ''' </summary>
  Protected Overrides Sub ApplicationStartup(container As TinyIoCContainer, pipelines As IPipelines)
    MyBase.ApplicationStartup(container, pipelines)

    ' from Nancy docs at https://github.com/NancyFx/Nancy/wiki/The-Application-Before,-After-and-OnError-pipelines:
    '   The After pipeline is defined using the same syntax as the Before pipeline, and the passed in parameter is
    '   also the current NancyContext. The difference is that the hook does not return a value...
    '   ...The After hooks does not have any return value because one has already been produced by the appropriate
    '   route. Instead you get the option to modify (Or completely replace) the existing response by accessing the
    '   Response property of the NancyContext that Is passed in.
    pipelines.AfterRequest.AddItemToEndOfPipeline(AddressOf CheckHtmlMinify)
  End Sub

  ''' <summary>
  ''' Check if the response content type is HTML, and if so, minify using WebMarkupMin.
  ''' </summary>
  Private Shared Sub CheckHtmlMinify(context As NancyContext)

    ' get the current response contents
    Dim contents = context.Response.Contents

    ' is the current response content type HTML?
    If context.Response.ContentType = "text/html" Then
      ' HTML minifier
      ' will use default config from web.config
      Dim htmlMinifier = New WebMarkupMin.Core.Minifiers.HtmlMinifier
      ' current HTML, initially empty
      Dim currentHtml As String = String.Empty

      ' read current response contents (HTML) from stream, get as string
      ' adapted from https://gist.github.com/chrisnicola/1147568,
      ' https://stackoverflow.com/questions/11718310/nancy-accessing-rewriting-response
      Using ms = New MemoryStream()
        contents.Invoke(ms)
        ' go to start of stream
        ms.Position = 0
        ' read stream to end
        Using reader = New StreamReader(ms)
          currentHtml = reader.ReadToEnd
        End Using
      End Using

      Try
        ' minify HTML string using WebMarkupMin
        ' see docs at https://webmarkupmin.codeplex.com/wikipage?title=WebMarkupMin%201.X#HtmlMinifier_Chapter
        ' will return object containing minified string (and errors, statistics)
        ' uses settings from web.config file webMarkupMin/webExtensions
        Dim minifiedHtml = htmlMinifier.Minify(currentHtml)

        ' set response contents to minified HTML
        ' this will overwrite current contents
        context.Response.Contents =
          Function(strm)
            ' create a new stream from the minified HTML string
            Using writer = New MemoryStream(System.Text.Encoding.UTF8.GetBytes(minifiedHtml.MinifiedContent))
              ' write the stream to the response
              writer.CopyTo(strm)
            End Using
          End Function

      Catch ex As Exception
        ' do something with error here
        ' left out for brevity
      End Try
    End If

  End Sub

End Class