Add timeline helpers to the HostContentUpdateEvent

Working out what event “belongs” to an edition is tricky, as Publishing
API doesn’t have the concept of editions. With this in mind we have a
bunch of logic:

- If an edition is superseded and the event happened after the edition
was superseded, it’s for a newer edition
- If an edition is published, and the event happened after the edition
was published AND the event is not for a newer edition, it’s for the
current edition
- If neither of the above is true, it’s for an older edition

app/models/host_content_update_event.rb

@@ -16,7 +16,17 @@ def self.all_for_date_window(document:, from:, to:)
     end
   end
 
-  private
+  def is_for_newer_edition?(edition)
+    edition.superseded? && created_at.after?(edition.superseded_at)
+  end
+
+  def is_for_current_edition?(edition)
+    edition.published_at && created_at.after?(edition.published_at) && !is_for_newer_edition?(edition)
+  end
+
+  def is_for_older_edition?(edition)
+    !is_for_newer_edition?(edition) && !is_for_current_edition?(edition)
+  end
 
   def self.get_user_for_uuid(uuid)
     User.find_by(uid: uuid)

test/unit/app/models/host_content_update_event_test.rb

@@ -74,4 +74,89 @@ class HostContentUpdateEventTest < ActiveSupport::TestCase
       assert_equal result.second.content_title, "Another exciting piece of content"
     end
   end
+
+  describe "Timeline helpers" do
+    let(:created_at) { Time.zone.now - 1.month }
+    let(:host_content_update_event) { build(:host_content_update_event, created_at:) }
+
+    describe "when the edition is published" do
+      let(:edition) { build(:edition) }
+
+      before do
+        edition.stubs(:published_at).returns(created_at - 12.months)
+      end
+
+      describe "when the event occurred after the edition was superseded" do
+        before do
+          edition.stubs(:superseded?).returns(true)
+          edition.stubs(:superseded_at).returns(created_at - 2.days)
+        end
+
+        describe "#is_for_newer_edition?" do
+          it "returns true" do
+            assert host_content_update_event.is_for_newer_edition?(edition)
+          end
+        end
+
+        describe "#is_for_current_edition?" do
+          it "returns false" do
+            assert_not host_content_update_event.is_for_current_edition?(edition)
+          end
+        end
+
+        describe "#is_for_older_edition?" do
+          it "returns false" do
+            assert_not host_content_update_event.is_for_older_edition?(edition)
+          end
+        end
+      end
+
+      describe "when the event occurred before the edition was superseded" do
+        before do
+          edition.stubs(:superseded?).returns(true)
+          edition.stubs(:superseded_at).returns(created_at + 2.days)
+        end
+
+        describe "#is_for_newer_edition?" do
+          it "returns false" do
+            assert_not host_content_update_event.is_for_newer_edition?(edition)
+          end
+        end
+
+        describe "#is_for_current_edition?" do
+          it "returns true" do
+            assert host_content_update_event.is_for_current_edition?(edition)
+          end
+        end
+
+        describe "#is_for_older_edition?" do
+          it "returns false" do
+            assert_not host_content_update_event.is_for_older_edition?(edition)
+          end
+        end
+      end
+    end
+
+    describe "when the edition is draft" do
+      let(:edition) { build(:edition, :draft) }
+
+      describe "#is_for_newer_edition?" do
+        it "returns false" do
+          assert_not host_content_update_event.is_for_newer_edition?(edition)
+        end
+      end
+
+      describe "#is_for_current_edition?" do
+        it "returns false" do
+          assert_not host_content_update_event.is_for_current_edition?(edition)
+        end
+      end
+
+      describe "#is_for_older_edition?" do
+        it "returns true" do
+          assert host_content_update_event.is_for_older_edition?(edition)
+        end
+      end
+    end
+  end
 end