Auto-append a cachebust URL to preview links

On the "preview" links we surface on the document summary screen,
we want to append a `?cachebust={timestamp}` parameter, where
`timestamp` is the current time in seconds (unix epoch time)

I have auto-appended a cachebust URL query parameter to:
- Normal document preview
- Translation preview

We get some confusing support tickets where multiple publishers
coalescee around the same document. A lot of the time, the
underlying reason for the support ticket is caching. For example,
two publishers previewing a document and seeing different things,
because one of them had an older version cached already.

Adding a cachebust string will force a fresh preview everytime
the publisher clicks on the preview link, which should minimise the
number of support tickets coming our way.

Author: kashifatcha

app/components/admin/editions/show/preview_component.html.erb

@@ -9,14 +9,14 @@
 
   <% if versioning_completed %>
     <p class="govuk-body">
-      <%= preview_link(primary_locale_link_text, local_edition.public_url(draft: true)) %>
+      <%= preview_link(primary_locale_link_text, local_edition.public_url({ draft: true }.merge(cachebust_url_options))) %>
     </p>
 
     <% if available_in_multiple_languages %>
       <% translation_preview_links = local_edition.non_primary_translation_locales.map do |locale|
         preview_link(
           "Preview on website - #{locale.native_and_english_language_name} (opens in new tab)",
-          local_edition.public_url(locale: locale.code, draft: true),
+          local_edition.public_url({ locale: locale.code, draft: true }.merge(cachebust_url_options)),
           )
       end %>
       <%= render "govuk_publishing_components/components/details", {

features/step_definitions/edition_update_slug_steps.rb

@@ -1,6 +1,6 @@
 Then(/^I can see the preview URL of the publication "([^"]*)" contains "([^"]*)"$/) do |title, new_slug|
   visit admin_edition_path(Publication.latest_edition.find_by!(title:))
-  expect(page).to have_link "Preview on website (opens in new tab)", href: "https://draft-origin.test.gov.uk/government/publications/#{new_slug}"
+  expect(page).to have_link "Preview on website (opens in new tab)", href: %r{\Ahttps://draft-origin\.test\.gov\.uk/government/publications/#{Regexp.escape(new_slug)}\?cachebust=\d+\z}
 end
 
 Then(/^I cannot see the option to keep the current page URL$/) do

features/step_definitions/policy_steps.rb

@@ -1,7 +1,7 @@
 Then(/^I should see a link to the preview version of the publication "([^"]*)"$/) do |publication_title|
   publication = Publication.find_by!(title: publication_title)
   visit admin_edition_path(publication)
-  expected_preview_url = "https://draft-origin.test.gov.uk/government/publications/#{publication.slug}"
+  expected_preview_url = %r{\Ahttps://draft-origin\.test\.gov\.uk/government/publications/#{Regexp.escape(publication.slug)}\?cachebust=\d+\z}
 
   expect(expected_preview_url).to eq(find("a[target='_blank']")[:href])
 end

test/components/admin/editions/show/preview_component_test.rb

@@ -23,25 +23,28 @@ class Admin::Editions::Show::PreviewComponentTest < ViewComponent::TestCase
 
   test "renders a link with tracking to preview the document when the edition is english only" do
     edition = build_stubbed(:publication, document: @document)
+    Admin::Editions::Show::PreviewComponent.any_instance.stubs(:cachebust_url_options).returns(cachebust: 123)
 
     render_inline(Admin::Editions::Show::PreviewComponent.new(edition:))
-    assert_selector "a[href='#{edition.public_url(draft: true)}']", text: "Preview on website (opens in new tab)"
+    assert_selector "a[href='#{edition.public_url(draft: true, cachebust: 123)}']", text: "Preview on website (opens in new tab)"
   end
 
   test "renders a link with tracking to preview the document when the edition is a foreign language only edition" do
     edition = build_stubbed(:publication, document: @document, primary_locale: :fr)
+    Admin::Editions::Show::PreviewComponent.any_instance.stubs(:cachebust_url_options).returns(cachebust: 123)
 
     render_inline(Admin::Editions::Show::PreviewComponent.new(edition:))
-    assert_selector "a[href='#{edition.public_url(draft: true)}']", text: "Preview on website (opens in new tab)"
+    assert_selector "a[href='#{edition.public_url(draft: true, cachebust: 123)}']", text: "Preview on website (opens in new tab)"
   end
 
   test "renders a link with tracking to preview the document for each translation when there are multiple translations" do
     edition = create(:publication, translated_into: %i[fr es], document: @document)
+    Admin::Editions::Show::PreviewComponent.any_instance.stubs(:cachebust_url_options).returns(cachebust: 123)
 
     render_inline(Admin::Editions::Show::PreviewComponent.new(edition:))
-    assert_selector "a[href='#{edition.public_url(draft: true)}']", text: "Preview on website - English (opens in new tab)"
-    assert_selector "a[href='#{edition.public_url(locale: 'fr', draft: true)}']", visible: false, text: "Preview on website - French (Français) (opens in new tab)"
-    assert_selector "a[href='#{edition.public_url(locale: 'es', draft: true)}']", visible: false, text: "Preview on website - Spanish (Español) (opens in new tab)"
+    assert_selector "a[href='#{edition.public_url(draft: true, cachebust: 123)}']", text: "Preview on website - English (opens in new tab)"
+    assert_selector "a[href='#{edition.public_url(locale: 'fr', draft: true, cachebust: 123)}']", visible: false, text: "Preview on website - French (Français) (opens in new tab)"
+    assert_selector "a[href='#{edition.public_url(locale: 'es', draft: true, cachebust: 123)}']", visible: false, text: "Preview on website - Spanish (Español) (opens in new tab)"
   end
 
   test "renders sharable preview functionality when edition is a pre-publication state" do