Enable taxonomy email signup for document collection

Allow users to sign up to a mapped taxonomy topic email subscription
from some document collection pages if taxonomy_topic_email_override
is present.

app/presenters/document_collection_presenter.rb

@@ -63,6 +63,10 @@ def group_heading(group)
     )
   end
 
+  def taxonomy_topic_email_override_base_path
+    content_item.dig("links", "taxonomy_topic_email_override", 0, "base_path")
+  end
+
 private
 
   def group_documents(group)

app/views/content_items/document_collection.html.erb

@@ -22,7 +22,11 @@
 </div>
 
 <%= render 'shared/publisher_metadata_with_logo' %>
-<%= render 'shared/single_page_notification_button', content_item: @content_item, skip_account: "true" %>
+<% if @content_item.taxonomy_topic_email_override_base_path.present? %>
+  <%= render 'shared/taxon_signup_link', base_path: @content_item.taxonomy_topic_email_override_base_path %>
+<% else %>
+  <%= render 'shared/single_page_notification_button', content_item: @content_item %>
+<% end %>
 
 <div class="govuk-grid-row">
   <div class="govuk-grid-column-two-thirds">

app/views/shared/_taxon_signup_link.html.erb

@@ -0,0 +1,17 @@
+<div
+  data-module="ga4-link-tracker"
+  data-ga4-link='{ "event_name": "navigation", "type": "subscribe", "index": { "index_link": 1 }, "index_total": 1, "section": "Top" }'
+  data-ga4-track-links-only
+>
+  <%= render "govuk_publishing_components/components/signup_link", {
+    link_text: "Get emails about this topic",
+    link_href: "/email-signup/?link=#{base_path}",
+    data: {
+      "module": "gem-track-click",
+      "track-category": "emailAlertLinkClicked",
+      "track-action": base_path,
+      "track-label": ""
+    },
+    margin_bottom: 6
+  } %>
+</div>

test/integration/document_collection_test.rb

@@ -158,4 +158,10 @@ class DocumentCollectionTest < ActionDispatch::IntegrationTest
     setup_and_visit_content_item("document_collection")
     assert page.has_css?(".gem-c-single-page-notification-button")
   end
+
+  test "renders with the taxonomy subscription button" do
+    setup_and_visit_content_item_with_taxonomy_topic_email_override("document_collection")
+    assert page.has_css?(".gem-c-signup-link")
+    assert_not page.has_css?(".gem-c-single-page-notification-button")
+  end
 end

test/test_helper.rb

@@ -195,6 +195,16 @@ def setup_and_visit_content_item_with_taxons(name, taxons)
     end
   end
 
+  def setup_and_visit_content_item_with_taxonomy_topic_email_override(name)
+    @content_item = get_content_example(name).tap do |item|
+      item["links"]["taxonomy_topic_email_override"] = [{
+        "base_path": "test",
+      }]
+      stub_content_store_has_item(item["base_path"], item.to_json)
+      visit_with_cachebust(item["base_path"])
+    end
+  end
+
   def setup_and_visit_notification_exempt_page(name)
     @content_item = get_content_example(name).tap do |item|
       item["content_id"] = ContentItem::SinglePageNotificationButton::EXEMPTION_LIST[0]