Add interactor to advance all teams stuck in single team matches

After playoffs are created, before saving the stage this interactor
goes to the intermediate stage, looks for all the matches that are
:single_team matches and populates the match below with their respective
"winner".

app/interactors/add_playoffs_to_tournament.rb

@@ -12,7 +12,8 @@ class AddPlayoffsToTournament
       else
         tournament.stages.concat playoff_stages
       end
-      context.object_to_save = tournament
+      context.intermediate_stage = tournament.stages.find(&:intermediate_stage?)
+      context.object_to_save = [tournament]
     else
       context.fail!
     end

app/interactors/advance_teams_in_intermediate_stage.rb

@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+class AdvanceTeamsInIntermediateStage
+  include Interactor
+
+  def call
+    intermediate_stage = context.intermediate_stage
+    return if intermediate_stage.nil?
+
+    intermediate_stage.matches.select { |m| m.state == 'single_team' }
+                      .each { |match| PopulateMatchBelowAndSave.call(match: match) }
+    context.object_to_save << intermediate_stage
+  end
+end

app/organizers/add_playoffs_to_tournament_and_save.rb

@@ -3,5 +3,5 @@
 class AddPlayoffsToTournamentAndSave
   include Interactor::Organizer
 
-  organize AddPlayoffsToTournament, SaveApplicationRecordObject
+  organize AddPlayoffsToTournament, AdvanceTeamsInIntermediateStage, SaveApplicationRecordObject
 end

spec/interactors/advance_teams_in_intermediate_stage_interactor_spec.rb

@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+RSpec.describe AdvanceTeamsInIntermediateStage do
+  context 'intermediate_stage is nil' do
+    let(:context) do
+      AdvanceTeamsInIntermediateStage.call(intermediate_stage: nil)
+    end
+
+    it 'succeeds' do
+      expect(context).to be_a_success
+    end
+
+    it 'doesn\'t call PopulateMatchBelow' do
+      expect(PopulateMatchBelowAndSave).not_to receive(:call)
+      context
+    end
+  end
+end