Remove duplicate global_bar_seen cookies

We had a bug which meant that the global_bar_seen cookie was sometimes set more than once.
This bug has now been fixed (#2026), but some users will be left with these duplicate cookies and therefore will continue to see the issue.

This commit introduces a function that checks for these duplicate cookies and deletes them if they're present.

app/assets/javascripts/global-bar-init.js

@@ -35,6 +35,32 @@ var globalBarInit = {
     return new RegExp(paths.join("|")).test(window.location.pathname)
   },
 
+  checkDuplicateCookie: function() {
+    var cookies = document.cookie.split(';')
+    var matches = 0
+
+    for (var i = 0; i < cookies.length; i++) {
+      if (cookies[i] && cookies[i].indexOf('global_bar_seen') !== -1) {
+        matches++
+      }
+    }
+
+    if (matches > 1) {
+      var possiblePaths = window.location.pathname.split("/")
+      var pathString= ""
+
+      // The duplicate cookie will have a path set to something other than "/".
+      // The cookie will only surface on that path or it's sub-paths
+      // As there isn't a way of directly finding out the path, we need to try cookie deletion with all path combinations possible on the current URL.
+      for (var i = 0; i < possiblePaths.length; i++) {
+        if (possiblePaths[i] !== "") {
+          pathString = pathString + "/" + possiblePaths[i]
+          document.cookie = 'global_bar_seen=; expires=Thu, 01 Jan 1970 00:00:01 GMT;path=' + pathString
+        }
+      }
+    }
+  },
+
   setBannerCookie: function() {
     var cookieCategory = window.GOVUK.getCookieCategory(GLOBAL_BAR_SEEN_COOKIE)
     var cookieConsent = GOVUK.getConsentCookie()
@@ -52,6 +78,11 @@ var globalBarInit = {
 
   init: function() {
     if (!globalBarInit.blacklistedUrl()) {
+      // We had a bug which meant that the global_bar_seen cookie was sometimes set more than once.
+      // This bug has now been fixed, but some users will be left with these duplicate cookies and therefore will continue to see the issue.
+      // We need to check for duplicate cookies so we can delete them
+      globalBarInit.checkDuplicateCookie()
+
       if (globalBarInit.getLatestCookie() === null) {
         globalBarInit.setBannerCookie()
         globalBarInit.makeBannerVisible()