Add analytics code trigger

- note that this change depends upon analytics code being in the components gem, which at time of writing is not complete
- analytics code is initialised on every page, if a previously set consent cookie is found, pageviews are sent
- the registration flow includes a yes/no radio for cookie consent, choosing 'yes' sets the cookie and immediately reinitialises the analytics code, firing a pageview
- if the user chooses 'no' that cookie is deleted
- this preference is not currently tied to the record in the user profile although this may change

app/assets/javascripts/analytics.js

@@ -0,0 +1,23 @@
+//= require govuk_publishing_components/analytics
+
+var linkedDomains = ['www.gov.uk']
+
+$(document).ready(function() {
+  if (typeof window.GOVUK.analyticsInit !== 'undefined') {
+    window.GOVUK.analyticsInit(linkedDomains)
+
+    $('.js-cookie-consent .govuk-radios__input').on('click', function() {
+      var response = $(this).val()
+
+      if (response === 'yes') {
+        window.GOVUK.approveAllCookieTypes()
+        window.GOVUK.cookie('cookies_preferences_set', 'true', { days: 365 })
+        window.GOVUK.analyticsInit(linkedDomains)
+      }
+
+      else {
+        window.GOVUK.deleteCookie('cookies_policy')
+      }
+    })
+  }
+})

app/assets/javascripts/application.js

@@ -4,3 +4,5 @@
 //= require govuk_publishing_components/components/checkboxes
 //= require govuk_publishing_components/components/error-summary
 //= require govuk_publishing_components/components/radio
+
+//= require ./analytics

app/views/devise/registrations/your_information.html.erb

@@ -19,24 +19,26 @@
 
     <%= form_with(url: new_user_registration_your_information_path(registration_state_id: @registration_state_id), method: :post) do %>
 
-      <%= render "govuk_publishing_components/components/radio", {
-        name: "cookie_consent",
-        heading: t("devise.registrations.your_information.fields.cookie_consent.heading"),
-        heading_size: "s",
-        error_message: devise_error_items(:cookie_consent, @resource_error_messages),
-        items: [
-          {
-            value: "yes",
-            text: t("devise.registrations.your_information.fields.cookie_consent.yes"),
-            checked: @consents.fetch(:cookie_consent_decision, nil) == "yes"
-          },
-          {
-            value: "no",
-            text: t("devise.registrations.your_information.fields.cookie_consent.no"),
-            checked: @consents.fetch(:cookie_consent_decision, nil) == "no"
-          }
-        ]
-      } %>
+      <div class="js-cookie-consent">
+        <%= render "govuk_publishing_components/components/radio", {
+          name: "cookie_consent",
+          heading: t("devise.registrations.your_information.fields.cookie_consent.heading"),
+          heading_size: "s",
+          error_message: devise_error_items(:cookie_consent, @resource_error_messages),
+          items: [
+            {
+              value: "yes",
+              text: t("devise.registrations.your_information.fields.cookie_consent.yes"),
+              checked: @consents.fetch(:cookie_consent_decision, nil) == "yes"
+            },
+            {
+              value: "no",
+              text: t("devise.registrations.your_information.fields.cookie_consent.no"),
+              checked: @consents.fetch(:cookie_consent_decision, nil) == "no"
+            }
+          ]
+        } %>
+      </div>
 
       <%= render "govuk_publishing_components/components/radio", {
         name: "feedback_consent",