Allow MMR triage delay for any future date before first dose

Previously, the validation for delayed MMR triage incorrectly checked
the minimum delay period even when the patient hadn't received their
first dose yet. This prevented nurses from scheduling triage delays
more than 28 days in the future for unvaccinated patients.

Now, the 28-day minimum delay validation only applies when the patient
has already received their first MMR dose and is awaiting their second.
For patients without any doses, any future date within the academic
year is accepted.

Author: jhenderson

app/forms/triage_form.rb

@@ -239,7 +239,8 @@ def validate_delay_vaccination_until_date
       )
     end
 
-    if programme.mmr? && (delay_vaccination_until < next_mmr_dose_date)
+    if programme.mmr? && patient_eligible_for_additional_dose? &&
+         (delay_vaccination_until < next_mmr_dose_date)
       errors.add(
         :delay_vaccination_until,
         "The vaccination cannot take place before #{next_mmr_dose_date.to_fs(:long)}"
@@ -255,4 +256,14 @@ def associate_triage_with_vaccination_record(next_dose_delay_triage)
       vaccination_record.update!(next_dose_delay_triage:)
     end
   end
+
+  def patient_eligible_for_additional_dose?
+    next_dose =
+      patient.vaccination_status(
+        programme: programme,
+        academic_year: session.academic_year
+      ).dose_sequence
+
+    next_dose == programme.maximum_dose_sequence
+  end
 end

spec/forms/triage_form_spec.rb

@@ -94,4 +94,52 @@
       expect(vaccination_record.reload.next_dose_delay_triage).to eq(triage)
     end
   end
+
+  context "programme is MMR" do
+    let(:programme) { create(:programme, :mmr) }
+
+    describe "validation for delay_vaccination_until" do
+      subject(:validation_errors) do
+        form.save # rubocop:disable Rails/SaveBang
+        form.errors.full_messages
+      end
+
+      let(:delay_vaccination_until) { nil }
+
+      let(:form) do
+        described_class.new(
+          patient:,
+          session:,
+          programme:,
+          delay_vaccination_until:,
+          current_user: create(:user),
+          status_option: "delay_vaccination"
+        )
+      end
+
+      context "patient hasn't received any doses" do
+        let(:delay_vaccination_until) { Date.tomorrow }
+
+        it "doesn't produce any validation errors" do
+          expect(validation_errors).to be_empty
+        end
+      end
+
+      context "patient has had their first dose" do
+        let(:delay_vaccination_until) { Date.tomorrow }
+
+        before do
+          create(:vaccination_record, patient:, programme:, session:)
+
+          StatusUpdater.call(patient:)
+        end
+
+        it "doesn't produce any validation errors" do
+          expect(validation_errors.join).to include(
+            "The vaccination cannot take place before"
+          )
+        end
+      end
+    end
+  end
 end