require 'rack'
require 'json'

module Mixpanel
  class Middleware
    class << self
      attr_accessor :skip_request
      def skip_this_request
        @skip_request = true
      end
    end

    @skip_request = false

    def initialize(app, mixpanel_token, options={})
      @app = app
      @token = mixpanel_token
      @options = {
        :insert_mixpanel_scripts=> true,
        :insert_js_last => false,
        :persist => false,
        :config => {}
      }.merge(options)
    end

    def call(env)
      @env = env

      @status, @headers, @response = @app.call(env)

      if is_trackable_response? && !Mixpanel::Middleware.skip_request
        merge_queue! if @options[:persist]
        update_response!
        update_content_length!
        delete_event_queue!
      end

      Mixpanel::Middleware.skip_request = false

      [@status, @headers, @response]
    end

    private

    def update_response!
      @response.each do |part|
        if is_regular_request? && is_html_response?
          insert_at = part.index(@options[:insert_js_last] ? '</body' : '</head')
          unless insert_at.nil?
            part.insert(insert_at, render_event_tracking_scripts) unless queue.empty?
            if @options[:insert_mixpanel_scripts]
              part.insert(insert_at, render_mixpanel_scripts) #This will insert the mixpanel initialization code before the queue of tracking events.
            end
          end
        elsif is_turbolink_request? && is_html_response?
          part.insert(part.index('</body'), render_event_tracking_scripts) unless queue.empty?
        elsif is_ajax_request? && is_html_response?
          part.insert(0, render_event_tracking_scripts) unless queue.empty?
        elsif is_ajax_request? && is_javascript_response?
          part.insert(0, render_event_tracking_scripts(false)) unless queue.empty?
        end
      end
    end

    def update_content_length!
      new_size = 0
      @response.each{|part| new_size += part.bytesize}
      @headers.merge!("Content-Length" => new_size.to_s)
    end

    def is_regular_request?
      !is_ajax_request? && !is_turbolink_request?
    end

    def is_turbolink_request?
      @env.has_key?("HTTP_X_XHR_REFERER")
    end

    def is_ajax_request?
      @env.has_key?("HTTP_X_REQUESTED_WITH") && @env["HTTP_X_REQUESTED_WITH"] == "XMLHttpRequest"
    end

    def is_html_response?
      @headers["Content-Type"].include?("text/html") if @headers.has_key?("Content-Type")
    end

    def is_javascript_response?
      @headers["Content-Type"].include?("text/javascript") if @headers.has_key?("Content-Type")
    end

    def is_trackable_response?
      return false if @status == 302
      return false if @env.has_key?("HTTP_SKIP_MIXPANEL_MIDDLEWARE")
      is_html_response? || is_javascript_response?
    end

    def render_mixpanel_scripts
      <<-EOT
        <!-- start Mixpanel -->
        <script type="text/javascript">
          (function(c,a){window.mixpanel=a;var b,d,h,e;b=c.createElement("script");
          b.type="text/javascript";b.async=!0;b.src=("https:"===c.location.protocol?"https:":"http:")+
          '//cdn.mxpnl.com/libs/mixpanel-2.1.min.js';d=c.getElementsByTagName("script")[0];
          d.parentNode.insertBefore(b,d);a._i=[];a.init=function(b,c,f){function d(a,b){
          var c=b.split(".");2==c.length&&(a=a[c[0]],b=c[1]);a[b]=function(){a.push([b].concat(
          Array.prototype.slice.call(arguments,0)))}}var g=a;"undefined"!==typeof f?g=a[f]=[]:
          f="mixpanel";g.people=g.people||[];h=['disable','track','track_pageview','track_links',
          'track_forms','register','register_once','unregister','identify','name_tag',
          'set_config','people.identify','people.set','people.increment'];for(e=0;e<h.length;e++)d(g,h[e]);
          a._i.push([b,c,f])};a.__SV=1.1;})(document,window.mixpanel||[]);

          mixpanel.init("#{@token}");
          mixpanel.set_config(#{@options[:config].to_json});
        </script>
        <!-- end Mixpanel -->
      EOT
    end

    def delete_event_queue!
      if @options[:persist]
        (@env['rack.session']).delete('mixpanel_events')
      else
        @env.delete('mixpanel_events')
      end
    end

    def queue
      if @options[:persist]
        return [] if !(@env['rack.session']).has_key?('mixpanel_events') || @env['rack.session']['mixpanel_events'].empty?
        @env['rack.session']['mixpanel_events']
      else
        return [] if !@env.has_key?('mixpanel_events') || @env['mixpanel_events'].empty?
        @env['mixpanel_events']
      end
    end

    def merge_queue!
      present_hash = {}
      special_events = ['identify', 'name_tag', 'people.set', 'register']
      queue.uniq!

      queue.reverse_each do |item|
        is_special = special_events.include?(item[0])
        if present_hash[item[0]] and is_special
          queue.delete(item)
        else
          present_hash[item[0]] = true if is_special
        end
      end
    end

    def render_event_tracking_scripts(include_script_tag=true)
      return "" if queue.empty?

      output = queue.map {|type, arguments| %(mixpanel.#{type}(#{arguments.join(', ')});) }.join("\n")
      output = "try {#{output}} catch(err) {};"

      include_script_tag ? "<script type='text/javascript'>#{output}</script>" : output
    end
  end
end