CLDC-1618 Add cookie banner (#973)

* CLDC-1618 Add cookie banner

* CLDC-1618 Add analytics script inclusion tests

* CLDC-1618 Include cookie banner JS

* CLDC-1618 Appease JS Standard

app/controllers/cookies_controller.rb

@@ -18,6 +18,12 @@ class CookiesController < ApplicationController
 
         redirect_to cookies_path
       end
+      format.json do
+        render json: {
+          status: "ok",
+          message: %(You’ve #{analytics_consent == 'on' ? 'accepted' : 'rejected'} analytics cookies.),
+        }
+      end
     end
   end
 

app/frontend/application.js

@@ -4,18 +4,19 @@
 // files to reference that code so it'll be compiled.
 
 // Polyfills for IE
+import '@stimulus/polyfills'
 import '@webcomponents/webcomponentsjs'
 import 'core-js/stable'
-import 'regenerator-runtime/runtime'
-import '@stimulus/polyfills'
 import 'custom-event-polyfill'
 import 'intersection-observer'
+import 'regenerator-runtime/runtime'
 
 //
 import { initAll as GOVUKFrontend } from 'govuk-frontend'
 import { initAll as GOVUKPrototypeComponents } from 'govuk-prototype-components'
-import './styles/application.scss'
 import './controllers'
+import './cookie-banner'
+import './styles/application.scss'
 
 require.context('govuk-frontend/govuk/assets')
 

app/frontend/cookie-banner.js

@@ -0,0 +1,57 @@
+const cookieBannerEl = document.querySelector('.js-cookie-banner')
+
+if (cookieBannerEl) {
+  const cookieFormEl = document.querySelector('.js-cookie-form')
+
+  cookieFormEl.addEventListener('click', (e) => {
+    if (e.target.tagName !== 'BUTTON') {
+      return
+    }
+
+    const body = new window.FormData(cookieFormEl)
+    body.append('cookies_form[accept_analytics_cookies]', e.target.value)
+
+    fetch(cookieFormEl.action, {
+      method: 'PUT',
+      headers: {
+        Accept: 'application/json'
+      },
+      body
+    })
+      .then((res) => {
+        if (res.status >= 200 && res.status < 300) {
+          return res
+        }
+
+        throw new Error(res)
+      })
+      .then((res) => res.json())
+      .then(({ message }) => {
+        const messageEl = cookieBannerEl.querySelector('.js-cookie-message')
+        messageEl.textContent = message
+
+        cookieBannerEl
+          .querySelector('.js-cookie-banner__form')
+          .setAttribute('hidden', '')
+        cookieBannerEl
+          .querySelector('.js-cookie-banner__success')
+          .removeAttribute('hidden')
+      })
+
+    const gaSrc = window.analyticsScript
+    if (e.target.value === 'on' && gaSrc) {
+      const scriptEl = document.createElement('script')
+      scriptEl.src = gaSrc
+      document.body.appendChild(scriptEl)
+    }
+
+    e.preventDefault()
+  })
+
+  const hideBannerEl = document.querySelector('.js-hide-cookie-banner')
+  hideBannerEl.addEventListener('click', (e) => {
+    e.preventDefault()
+
+    cookieBannerEl.setAttribute('hidden', '')
+  })
+}

app/views/cookies/_banner.html.erb

@@ -0,0 +1,48 @@
+<div class="govuk-cookie-banner js-cookie-banner" role="region" aria-label="Cookies on CORE">
+  <div class="govuk-cookie-banner__message govuk-width-container js-cookie-banner__form">
+    <div class="govuk-grid-row">
+      <div class="govuk-grid-column-two-thirds">
+        <h2 class="govuk-cookie-banner__heading govuk-heading-m">Cookies on CORE</h2>
+
+        <div class="govuk-cookie-banner__content">
+          <p class="govuk-body">We use some essential cookies to make this service work.</p>
+          <p class="govuk-body">We’d like to use analytics cookies so we can understand how you use the service and make improvements.</p>
+        </div>
+      </div>
+    </div>
+
+    <%= form_with url: cookies_path, class: "js-cookie-form", method: :put do |f| %>
+      <div class="govuk-button-group">
+        <button type="submit" class="govuk-button" name="cookies_form[analytics_consent]" value="on">
+          Accept analytics cookies
+        </button>
+        <button type="submit" class="govuk-button" name="cookies_form[analytics_consent]" value="off">
+          Reject analytics cookies
+        </button>
+        <%= govuk_link_to "View cookies", cookies_path %>
+      </div>
+    <% end %>
+  </div>
+
+  <div class="govuk-cookie-banner__message govuk-width-container js-cookie-banner__success" role="alert" hidden>
+    <div class="govuk-grid-row">
+      <div class="govuk-grid-column-two-thirds">
+
+        <div class="govuk-cookie-banner__content">
+          <p class="govuk-body">
+            <span class="js-cookie-message">
+              You’ve set your cookie preferences.
+            </span>
+            You can <%= govuk_link_to "change your cookie settings", cookies_path %> at any time.
+          </p>
+        </div>
+      </div>
+    </div>
+
+    <div class="govuk-button-group">
+      <button class="govuk-button js-hide-cookie-banner">
+        Hide this message
+      </button>
+    </div>
+  </div>
+</div>

app/views/layouts/application.html.erb

@@ -25,6 +25,7 @@
     <% gtm_container = get_gtm_container %>
     <% gtm_id = get_gtm_id %>
 
+    <% if cookies[:accept_analytics_cookies] == "on" %>
       <!-- Google Tag Manager (doesn't store personal info until permission given) -->
       <script>(function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':
       new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],
@@ -33,7 +34,6 @@
       })(window,document,'script','dataLayer','<%= gtm_container %>');</script>
       <!-- End Google Tag Manager -->
 
-    <% if cookies[:accept_analytics_cookies] == "on" %>
       <script async src="https://www.googletagmanager.com/gtag/js?id=<%= gtm_id %>"></script>
     <% else %>
       <script>
@@ -72,13 +72,17 @@
       document.body.className = ((document.body.className) ? document.body.className + " js-enabled" : "js-enabled");
     </script>
 
+    <% if cookies[:accept_analytics_cookies] == "on" %>
       <!-- Google Tag Manager (noscript) -->
-    <% if cookies[:accept_analytics_cookies] %>
       <noscript>
         <iframe src="https://www.googletagmanager.com/ns.html?id=<% gtm_container %>" height="0" width="0" style="display:none;visibility:hidden"></iframe>
       </noscript>
     <% end %>
 
+    <% unless cookies[:accept_analytics_cookies] || current_page?(cookies_path) %>
+      <%= render "cookies/banner" %>
+    <% end %>
+
     <%= govuk_skip_link %>
 
     <%= govuk_header(

spec/views/layouts/application_layout_spec.rb

@@ -0,0 +1,57 @@
+require "rails_helper"
+
+RSpec.describe "layouts/application" do
+  shared_examples "analytics cookie elements" do |banner:, scripts:|
+    define_negated_matcher :not_match, :match
+
+    it "#{banner ? 'includes' : 'omits'} the cookie banner" do
+      banner_text = "We’d like to use analytics cookies so we can understand how you use the service and make improvements."
+      if banner
+        expect(rendered).to match(banner_text)
+      else
+        expect(rendered).not_to match(banner_text)
+      end
+    end
+
+    it "#{scripts ? 'includes' : 'omits'} the analytics scripts" do
+      gtm_script_tag = /<script.*googletagmanager/
+      gtm_iframe_tag = /<iframe.*googletagmanager/
+      if scripts
+        expect(rendered).to match(gtm_script_tag).and match(gtm_iframe_tag)
+      else
+        expect(rendered).to not_match(gtm_script_tag).and not_match(gtm_iframe_tag)
+      end
+    end
+  end
+
+  context "with no cookie set" do
+    before do
+      cookies[:accept_analytics_cookies] = nil
+      render
+    end
+
+    include_examples "analytics cookie elements", banner: true, scripts: false
+
+    it "sets window.analyticsScript for the JS to refer to if the user accepts" do
+      expect(rendered).to match(/window\.analyticsScript = "https:\/\/www\.googletagmanager\.com\/gtag\/js\?id=G-[\w\d]+"/)
+    end
+  end
+
+  context "with analytics accepted" do
+    before do
+      cookies[:accept_analytics_cookies] = "on"
+      render
+    end
+
+    include_examples "analytics cookie elements", banner: false, scripts: true
+  end
+
+  context "with analytics rejected" do
+    before do
+      cookies[:accept_analytics_cookies] = "off"
+      render
+    end
+
+    include_examples "analytics cookie elements", banner: false, scripts: false
+  end
+end