Expose multi cohort in admin dashboard

We want it to be clear in the admin dashboard participants view when a
participant has migrated from a cohort due to the payments being frozen.

app/helpers/admin_helper.rb

@@ -54,7 +54,6 @@ def admin_participant_header_and_title(presenter:, section:)
     full_name = profile.full_name
     role = admin_participant_role_name(profile.class.name)
     trn = profile.teacher_profile.trn
-    start_year = presenter.start_year
 
     visually_hidden = tag.span(" - #{section}", class: "govuk-visually-hidden")
 
@@ -75,7 +74,7 @@ def admin_participant_header_and_title(presenter:, section:)
         safe_join(
           [
             tag.span("Cohort: ", class: "govuk-body govuk-!-font-weight-bold"),
-            start_year,
+            presenter.detailed_cohort_information,
           ],
         )
       end,

app/presenters/admin/participant_presenter.rb

@@ -21,6 +21,19 @@ def cohort
     relevant_cohort_location.cohort
   end
 
+  def detailed_cohort_information
+    current_cohort = cohort.start_year
+
+    return current_cohort unless participant_profile.cohort_changed_after_payments_frozen
+
+    original_cohort = participant_profile.participant_declarations
+      .includes(:cohort)
+      .where.not(cohort: { start_year: current_cohort })
+      .pick("cohort.start_year")
+
+    "#{current_cohort} (migrated after #{original_cohort || 'unknown cohort'} payments were frozen)"
+  end
+
   def declarations
     @declarations ||= @participant_profile
                         .participant_declarations

spec/presenters/admin/participant_presenter_spec.rb

@@ -136,6 +136,38 @@
         end
       end
 
+      describe "#detailed_cohort_information" do
+        let(:participant_profile) { create(:ect) }
+        let(:cohort) { participant_profile.schedule.cohort }
+        let(:detailed_cohort_information) { subject.detailed_cohort_information }
+
+        context "when the participant has not had cohort_changed_after_payments_frozen" do
+          before { participant_profile.update!(cohort_changed_after_payments_frozen: false) }
+
+          it { expect(detailed_cohort_information).to eq(cohort.start_year) }
+        end
+
+        context "when the participant has had cohort_changed_after_payments_frozen" do
+          before { participant_profile.update!(cohort_changed_after_payments_frozen: true) }
+
+          context "when the previous cohort cannot be determined" do
+            it { expect(detailed_cohort_information).to eq("#{cohort.start_year} (migrated after unknown cohort payments were frozen)") }
+          end
+
+          context "when the previous cohort can be determined" do
+            let(:previous_cohort) { Cohort.previous }
+            let(:cpd_lead_provider) { participant_profile.lead_provider.cpd_lead_provider }
+            let(:course_identifier) { "ecf-induction" }
+
+            before do
+              create(:participant_declaration, participant_profile:, cohort: previous_cohort, state: :paid, cpd_lead_provider:, course_identifier:)
+            end
+
+            it { expect(detailed_cohort_information).to eq("#{cohort.start_year} (migrated after #{previous_cohort.start_year} payments were frozen)") }
+          end
+        end
+      end
+
       describe "#start_year" do
         it "returns the start_year via induction record, school cohort and cohort" do
           expect(subject.start_year).to eql(subject.relevant_induction_record.school_cohort.cohort.start_year)