Remove AP specifc logic from page sequence

Previously the page sequence contained specific logic for handling an
additional payments sub journey (traniee teacher), and rather than
modifying the slug sequence just overwrote what is returned.
Additionally there was a condition in the slug sequence that caused the
whole thing to be swapped out if we were dealing with a trainee teacher.
This commit removes the additional payments specific handling from the
page sequence, leaving it journey agnostic, and updates the additional
payments slug sequence to move the trainee teacher sub journey branching
to the top level.

app/models/journeys/additional_payments_for_teaching/slug_sequence.rb

@@ -73,6 +73,15 @@ class SlugSequence
         RESULTS_SLUGS
       ).freeze
 
+      TRAINEE_TEACHER_SLUGS = %w[
+        current-school
+        nqt-in-academic-year-after-itt
+        eligible-itt-subject
+        eligible-degree-subject
+        future-eligibility
+        ineligible
+      ]
+
       attr_reader :journey_session
 
       delegate :answers, to: :journey_session
@@ -81,9 +90,15 @@ def initialize(journey_session)
         @journey_session = journey_session
       end
 
-      # Even though we are inside the ECP namespace, this method can modify the
-      # slug sequence of both LUP and ECP claims
       def slugs
+        if answers.trainee_teacher? && Policies::LevellingUpPremiumPayments::SchoolEligibility.new(answers.current_school).eligible?
+          lup_trainee_journey_slugs
+        else
+          non_trainee_journey_slugs
+        end
+      end
+
+      def non_trainee_journey_slugs
         SLUGS.dup.tap do |sequence|
           if !Journeys::AdditionalPaymentsForTeaching.configuration.teacher_id_enabled?
             sequence.delete("sign-in-or-continue")
@@ -132,14 +147,9 @@ def slugs
             sequence.delete("mobile-verification")
           end
 
-          if answers.trainee_teacher?
-            trainee_teacher_slugs!(sequence)
-            sequence.delete("eligible-degree-subject") unless lup_eligibility_checker.indicated_ineligible_itt_subject?
-          else
-            sequence.delete("ineligible") unless [:ineligible, :eligible_later].include?(overall_eligibility_status)
-            sequence.delete("future-eligibility")
-            sequence.delete("eligible-degree-subject") unless ecp_eligibility_checker.status == :ineligible && lup_eligibility_checker.indicated_ineligible_itt_subject?
-          end
+          sequence.delete("ineligible") unless [:ineligible, :eligible_later].include?(overall_eligibility_status)
+          sequence.delete("future-eligibility")
+          sequence.delete("eligible-degree-subject") unless ecp_eligibility_checker.status == :ineligible && lup_eligibility_checker.indicated_ineligible_itt_subject?
 
           sequence.delete("induction-completed") unless induction_question_required?
 
@@ -164,6 +174,14 @@ def slugs
         end
       end
 
+      def lup_trainee_journey_slugs
+        TRAINEE_TEACHER_SLUGS.dup.tap do |sequence|
+          if lup_eligibility_checker.status == :eligible_later && answers.eligible_degree_subject.nil?
+            sequence.delete("eligible-degree-subject")
+          end
+        end
+      end
+
       def self.start_page_url
         Rails.application.routes.url_helpers.landing_page_path("additional-payments")
       end
@@ -190,21 +208,6 @@ def replace_ecp_only_induction_not_completed_slugs(sequence)
         sequence.replace(slugs)
       end
 
-      # This method swaps out the entire slug sequence and replaces it with this tiny
-      # journey.
-      def trainee_teacher_slugs!(sequence)
-        trainee_slugs = %w[
-          current-school
-          nqt-in-academic-year-after-itt
-          eligible-itt-subject
-          eligible-degree-subject
-          future-eligibility
-          ineligible
-        ]
-
-        [sequence.dup - trainee_slugs].flatten.each { |slug| sequence.delete(slug) }
-      end
-
       def induction_question_required?
         # Induction question is not required if an ECP-eligible school is not selected.
         return false unless ecp_school_selected?

app/models/journeys/page_sequence.rb

@@ -22,10 +22,6 @@ def slugs
     def next_slug
       return "ineligible" if journey_ineligible?
 
-      if lup_policy_and_trainee_teacher_at_lup_school?
-        return handle_trainee_teacher
-      end
-
       if claim_submittable?
         return "student-loan-amount" if updating_personal_details? && in_sequence?("student-loan-amount")
         return "check-your-answers"
@@ -87,29 +83,6 @@ def can_skip_next_slug?
       true if current_slug == "select-home-address" && answers.postcode.present?
     end
 
-    def lup_policy_and_trainee_teacher_at_lup_school?
-      journey == Journeys::AdditionalPaymentsForTeaching && lup_trainee_at_lup_school
-    end
-
-    def lup_trainee_at_lup_school
-      answers.nqt_in_academic_year_after_itt == false && Policies::LevellingUpPremiumPayments::SchoolEligibility.new(answers.current_school).eligible?
-    end
-
-    def handle_trainee_teacher
-      case current_slug
-      when "nqt-in-academic-year-after-itt"
-        "eligible-itt-subject"
-      when "eligible-itt-subject"
-        if answers.eligible_itt_subject.to_sym.in? Policies::LevellingUpPremiumPayments.fixed_subject_symbols
-          "future-eligibility"
-        else
-          "eligible-degree-subject"
-        end
-      when "eligible-degree-subject"
-        "future-eligibility"
-      end
-    end
-
     def current_slug_index
       slugs.index(current_slug) || 0
     end