Embeds javascript into the head to track page view with app insights

lib/application_insights.rb

@@ -5,5 +5,6 @@ require_relative 'application_insights/version'
 module ApplicationInsights
   module Rack
     autoload :TrackRequest, "application_insights/rack/track_request"
+    autoload :TrackPageView, "application_insights/rack/track_page_view"
   end
 end

lib/application_insights/rack/track_page_view.rb

@@ -0,0 +1,44 @@
+require 'rack'
+
+module ApplicationInsights
+  module Rack
+    class TrackPageView
+      def initialize(app, instrumentation_key)
+        @app = app
+        @instrumentation_key = instrumentation_key
+      end
+
+      def call(env)
+        status, headers, response = @app.call(env)
+
+        content_type = headers['Content-Type']
+        return [status, headers, response] unless content_type && content_type.include?('text/html')
+
+        unless response.is_a?(::Rack::Response)
+          response = ::Rack::Response.new(response, status, headers)
+        end
+        new_response = ::Rack::Response.new([], response.status, response.headers)
+        response.body.each do |b|
+          new_response.write(b.sub(/<\/head>/, "\n#{embedded_script_code}\n</head>"))
+        end
+
+        [new_response.status, new_response.headers, new_response]
+      end
+
+      private
+      def embedded_script_code
+        <<~"SCRIPT"
+          <script type="text/javascript">
+          var appInsights=window.appInsights||function(a){
+            function b(a){c[a]=function(){var b=arguments;c.queue.push(function(){c[a].apply(c,b)})}}var c={config:a},d=document,e=window;setTimeout(function(){var b=d.createElement("script");b.src=a.url||"https://az416426.vo.msecnd.net/scripts/a/ai.0.js",d.getElementsByTagName("script")[0].parentNode.appendChild(b)});try{c.cookie=d.cookie}catch(a){}c.queue=[];for(var f=["Event","Exception","Metric","PageView","Trace","Dependency"];f.length;)b("track"+f.pop());if(b("setAuthenticatedUserContext"),b("clearAuthenticatedUserContext"),b("startTrackEvent"),b("stopTrackEvent"),b("startTrackPage"),b("stopTrackPage"),b("flush"),!a.disableExceptionTracking){f="onerror",b("_"+f);var g=e[f];e[f]=function(a,b,d,e,h){var i=g&&g(a,b,d,e,h);return!0!==i&&c["_"+f](a,b,d,e,h),i}}return c
+            }({
+                instrumentationKey:"#{@instrumentation_key}"
+            });
+
+          window.appInsights=appInsights,appInsights.queue&&0===appInsights.queue.length&&appInsights.trackPageView();
+          </script>
+        SCRIPT
+      end
+    end
+  end
+end