Fix draft locale deletion bug in Publishing API

When changing the primary locale of a draft (e.g. from English to
French), the draft for the previous locale was not being discarded in
Publishing API, leaving orphaned drafts.

This commit:
- Captures dirty attributes in `EditionService` before reload.
- Passes the previous primary locale to `PublishingApiPusher`.
- Upates `PublishingApiPusher` to discard the previous locale draft
  during `update_draft` event if the primary locale has changed.
- Adds regression tests in `DraftLocaleSwitchTest`.

Jira: https://gov-uk.atlassian.net/browse/WHIT-2842

Author: MuriloDalRi

app/services/edition_service.rb

@@ -51,9 +51,14 @@ def notify!
   end
 
   def update_publishing_api!
+    options_for_publishing_api_pusher = options
+    if edition.saved_change_to_primary_locale?
+      options_for_publishing_api_pusher[:primary_locale_before_last_save] = edition.primary_locale_before_last_save
+    end
+
     ServiceListeners::PublishingApiPusher
       .new(edition.reload)
-      .push(event: verb, options:)
+      .push(event: verb, options: options_for_publishing_api_pusher)
   end
 
   def prepare_edition

app/services/service_listeners/publishing_api_pusher.rb

@@ -37,10 +37,15 @@ def push(event:, options: {})
       end
 
       handle_associated_documents(event)
+      handle_locale_change(options[:primary_locale_before_last_save]) if options.key?(:primary_locale_before_last_save)
     end
 
   private
 
+    def handle_locale_change(previous_locale)
+      api.discard_translation_async(edition, locale: previous_locale)
+    end
+
     def handle_associated_documents(event)
       if edition.respond_to?(:associated_documents) || edition.respond_to?(:deleted_associated_documents)
         PublishingApiAssociatedDocuments.process(edition, event)

test/unit/app/services/draft_locale_switch_test.rb

@@ -0,0 +1,44 @@
+require "test_helper"
+
+class DraftLocaleSwitchTest < ActiveSupport::TestCase
+  test "updates Publishing API when changing primary locale of a draft" do
+    edition = create(:draft_document_collection, title: "English Title", primary_locale: "en")
+    edition.primary_locale = "fr"
+    edition.save!
+
+    Whitehall::PublishingApi.expects(:patch_links).at_least_once
+
+    Whitehall::PublishingApi.expects(:save_draft_translation).with(
+      anything,
+      :fr,
+      nil,
+      bulk_publishing: false,
+    )
+
+    Whitehall::PublishingApi.expects(:discard_translation_async).with(
+      anything,
+      locale: "en",
+    )
+
+    DraftEditionUpdater.new(edition, current_user: create(:user)).perform!
+  end
+
+  test "does not discard translation when primary locale is unchanged" do
+    edition = create(:draft_document_collection, title: "English Title", primary_locale: "en")
+    edition.title = "New Title"
+    edition.primary_locale = "en"
+    edition.save!
+
+    Whitehall::PublishingApi.expects(:patch_links).at_least_once
+    Whitehall::PublishingApi.expects(:save_draft_translation).with(
+      anything,
+      :en,
+      nil,
+      bulk_publishing: false,
+    )
+
+    Whitehall::PublishingApi.expects(:discard_translation_async).never
+
+    DraftEditionUpdater.new(edition, current_user: create(:user)).perform!
+  end
+end