Add new cookie banner code.

Copies HTML and Sass from GOV.UK Pubishing
components cookie-banner with changes to content
and functionality to better suit Notify.

Changes are:
- adds a 'reject' button which the GOV.UK
  code doesn't have
- adds Sass from the GOV.UK Frontend button
  component which the GOV.UK version used so
  is included here
- removed click tracking from cookie banner

app/assets/javascripts/cookieMessage.js

@@ -1,16 +1,90 @@
-(function () {
-  "use strict";
+window.GOVUK = window.GOVUK || {};
+window.GOVUK.Modules = window.GOVUK.Modules || {};
 
-  var root = this;
-  if(typeof root.GOVUK === 'undefined') { root.GOVUK = {}; }
+(function (Modules) {
+  function CookieBanner () { }
 
-  GOVUK.addCookieMessage = function () {
-    var message = document.getElementById('global-cookie-message'),
-        hasCookieMessage = (message && GOVUK.cookie('seen_cookie_message') === null);
+  CookieBanner.prototype.start = function ($module) {
+    this.$module = $module[0];
+    this.$module.hideCookieMessage = this.hideCookieMessage.bind(this);
+    this.$module.showConfirmationMessage = this.showConfirmationMessage.bind(this);
+    this.$module.setCookieConsent = this.setCookieConsent.bind(this);
 
-    if (hasCookieMessage) {
-      message.style.display = 'block';
-      GOVUK.cookie('seen_cookie_message', 'yes', { days: 28 });
+    this.$module.cookieBanner = document.querySelector('.notify-cookie-banner');
+    this.$module.cookieBannerConfirmationMessage = this.$module.querySelector('.notify-cookie-banner__confirmation');
+
+    this.setupCookieMessage();
+  };
+
+  CookieBanner.prototype.setupCookieMessage = function () {
+    this.$hideLink = this.$module.querySelector('button[data-hide-cookie-banner]');
+    if (this.$hideLink) {
+      this.$hideLink.addEventListener('click', this.$module.hideCookieMessage);
+    }
+
+    this.$acceptCookiesLink = this.$module.querySelector('button[data-accept-cookies=true]');
+    if (this.$acceptCookiesLink) {
+      this.$acceptCookiesLink.addEventListener('click', () => this.$module.setCookieConsent(true));
+    }
+
+    this.$rejectCookiesLink = this.$module.querySelector('button[data-accept-cookies=false]');
+    if (this.$rejectCookiesLink) {
+      this.$rejectCookiesLink.addEventListener('click', () => this.$module.setCookieConsent(false));
+    }
+
+    this.showCookieMessage();
+  };
+
+  CookieBanner.prototype.showCookieMessage = function () {
+    // Show the cookie banner if not in the cookie settings page
+    if (!this.isInCookiesPage()) {
+      var hasCookiesPolicy = window.GOVUK.cookie('cookies_policy');
+      var shouldHaveCookieMessage = (this.$module && !hasCookiesPolicy);
+
+      if (shouldHaveCookieMessage) {
+        this.$module.style.display = 'block';
+      } else {
+        this.$module.style.display = 'none';
+      }
+    } else {
+      this.$module.style.display = 'none';
     }
   };
-}).call(this);
+
+  CookieBanner.prototype.hideCookieMessage = function (event) {
+    if (this.$module) {
+      this.$module.style.display = 'none';
+    }
+
+    if (event.target) {
+      event.preventDefault();
+    }
+  };
+
+  CookieBanner.prototype.setCookieConsent = function (analyticsConsent) {
+    window.GOVUK.setConsentCookie({ 'analytics': analyticsConsent });
+
+    this.$module.showConfirmationMessage(analyticsConsent);
+    this.$module.cookieBannerConfirmationMessage.focus();
+
+    if (analyticsConsent) { window.GOVUK.initAnalytics(); }
+  };
+
+  CookieBanner.prototype.showConfirmationMessage = function (analyticsConsent) {
+    var messagePrefix = analyticsConsent ? 'You’ve accepted analytics cookies.' : 'You told us not to use analytics cookies.';
+
+    this.$cookieBannerMainContent = document.querySelector('.notify-cookie-banner__wrapper');
+    this.$cookieBannerConfirmationMessage = document.querySelector('.notify-cookie-banner__confirmation-message');
+
+    this.$cookieBannerConfirmationMessage.insertAdjacentText('afterbegin', messagePrefix);
+    this.$cookieBannerMainContent.style.display = 'none';
+    this.$module.cookieBannerConfirmationMessage.style.display = 'block';
+  };
+
+  CookieBanner.prototype.isInCookiesPage = function () {
+    return window.location.pathname === '/cookies';
+  };
+
+  Modules.CookieBanner = CookieBanner;
+})(window.GOVUK.Modules);
+