Use the ContentBlockDetector in the presenter

This allows us to send the content IDs of any content blocks that are
used in a smart answer as links, so Content Block Manager knows that
the blocks are used in a particular Smart Answer.

Author: pezholio

app/presenters/content_item_presenter.rb

@@ -25,7 +25,8 @@ def payload
       routes: [
         { type: "prefix", path: base_path },
       ],
-    }
+      links:,
+    }.compact
   end
 
 private
@@ -37,4 +38,12 @@ def start_node_presenter
   def base_path
     "/#{flow.name}"
   end
+
+  def links
+    embed_content_ids.any? ? { embed: embed_content_ids } : nil
+  end
+
+  def embed_content_ids
+    @embed_content_ids ||= ContentBlockDetector.new(flow).content_blocks.map(&:content_id).uniq
+  end
 end

test/unit/content_item_presenter_test.rb

@@ -28,5 +28,35 @@ class ContentItemPresenterPresenterTest < ActiveSupport::TestCase
       assert_equal "The Gorge of Eternal Peril!!!", payload[:description]
       assert_match %r{He who would cross the Bridge of Death}, payload.dig(:details, :hidden_search_terms, 0)
     end
+
+    context "when the ContentBlockDetector finds associated content blocks" do
+      setup do
+        @content_id = SecureRandom.uuid
+        content_block_1 = stub("content_block", content_id: @content_id)
+        content_block_2 = stub("content_block", content_id: @content_id)
+
+        detector = stub("detector", content_blocks: [content_block_1, content_block_2])
+        ContentBlockDetector.expects(:new).with(@flow).returns(detector)
+      end
+
+      should "include an array of unique content IDs in the payload" do
+        payload = ContentItemPresenter.new(@flow).payload
+
+        assert_equal [@content_id], payload[:links][:embed]
+      end
+    end
+
+    context "when the ContentBlockDetector does not find associated content blocks" do
+      setup do
+        detector = stub("detector", content_blocks: [])
+        ContentBlockDetector.expects(:new).with(@flow).returns(detector)
+      end
+
+      should "not include any links" do
+        payload = ContentItemPresenter.new(@flow).payload
+
+        assert_nil payload[:links]
+      end
+    end
   end
 end