refactor on deriving and clearing invalid derived values on sales log

app/models/derived_variables/sales_log_variables.rb

@@ -1,5 +1,7 @@
 module DerivedVariables::SalesLogVariables
   def set_derived_fields!
+    reset_invalidated_derived_values!
+
     self.ethnic = 17 if ethnic_refused?
     self.mscharge = nil if no_monthly_leasehold_charges?
     if exdate.present?
@@ -13,9 +15,6 @@ module DerivedVariables::SalesLogVariables
       self.hoyear = hodate.year
     end
     self.deposit = value if outright_sale? && mortgage_not_used?
-    if mortgage_not_used?
-      self.mortgage = 0
-    end
     self.pcode1, self.pcode2 = postcode_full.split(" ") if postcode_full.present?
     self.totchild = total_child
     self.totadult = total_adult + total_elder
@@ -31,20 +30,73 @@ module DerivedVariables::SalesLogVariables
       self.uprn_known = 0
     end
 
-    if buyers_will_not_live_in?
-      self.buy1livein = 2
-      if joint_purchase?
-        self.buy2livein = 2
+    set_encoded_derived_values!
+  end
+
+private
+
+  DEPENDENCIES = [
+    {
+      conditions: {
+        buylivein: 2,
+      },
+      derived_values: {
+        buy1livein: 2,
+      }
+    },
+    {
+      conditions: {
+        buylivein: 2,
+        jointpur: 1,
+      },
+      derived_values: {
+        buy1livein: 2,
+        buy2livein: 2,
+      }
+    },
+    {
+      conditions: {
+        buylivein: 1,
+        jointpur: 2,
+      },
+      derived_values: {
+        buy1livein: 1,
+      },
+    },
+    {
+      conditions: {
+        mortgageused: 2,
+      },
+      derived_values: {
+        mortgage: 0,
+      },
+    },
+  ].freeze
+
+  def reset_invalidated_derived_values!
+    DEPENDENCIES.each do |dependency|
+      any_conditions_changed = dependency[:conditions].any? { |attribute, _value| send("#{attribute}_changed?") }
+      next unless any_conditions_changed
+
+      previously_in_derived_state = dependency[:conditions].all? { |attribute, value| send("#{attribute}_was") == value }
+      next unless previously_in_derived_state
+
+      dependency[:derived_values].each do |derived_attribute, _derived_value|
+        Rails.logger.debug("Cleared derived #{derived_attribute} value")
+        send("#{derived_attribute}=", nil)
       end
     end
+  end
 
-    if buyers_will_live_in? && not_joint_purchase?
-      self.buy1livein = 1
+  def set_encoded_derived_values!
+    DEPENDENCIES.each do |dependency|
+      derivation_applies = dependency[:conditions].all? { |attribute, value| send(attribute) == value }
+      if derivation_applies
+        dependency[:derived_values].each { |attribute, value| send("#{attribute}=", value) }
+      end
     end
   end
 
-private
-
   def number_of_household_members
     return unless hholdcount.present? && jointpur.present?
 

app/models/sales_log.rb

@@ -26,7 +26,6 @@ class SalesLog < Log
 
   validates_with SalesLogValidator
   before_validation :recalculate_start_year!, if: :saledate_changed?
-  before_validation :reset_invalidated_dependent_fields!
   before_validation :process_postcode_changes!, if: :postcode_full_changed?
   before_validation :process_previous_postcode_changes!, if: :ppostcode_full_changed?
   before_validation :reset_location_fields!, unless: :postcode_known?
@@ -373,43 +372,4 @@ class SalesLog < Log
     when 3 then "outright sale"
     end
   end
-
-private
-
-  def reset_invalidated_dependent_fields!
-    super
-
-    reset_derived_questions!
-  end
-
-  def reset_derived_questions!
-    dependencies = [
-      {
-        conditions: {
-          buylivein: 2,
-        },
-        derived_attributes: %i[buy1livein buy2livein],
-      },
-      {
-        conditions: {
-          buylivein: 1,
-          jointpur: 1,
-        },
-        derived_attributes: [:buy1livein],
-      },
-    ]
-
-    dependencies.each do |dependency|
-      any_primary_attributes_changed = dependency[:conditions].any? { |attribute, _value| send("#{attribute}_changed?") }
-      next unless any_primary_attributes_changed
-
-      previously_in_derived_state = dependency[:conditions].all? { |attribute, value| send("#{attribute}_was") == value }
-      next unless previously_in_derived_state
-
-      dependency[:derived_attributes].each do |derived_attribute|
-        Rails.logger.debug("Cleared derived #{derived_attribute} value")
-        send("#{derived_attribute}=", nil)
-      end
-    end
-  end
 end

spec/models/sales_log_spec.rb

@@ -221,6 +221,15 @@ RSpec.describe SalesLog, type: :model do
       expect(record_from_db["mortgage"]).to eq(0.0)
     end
 
+    it "clears mortgage value if mortgage used is changed from no to yes" do
+      # to avoid log failing validations when mortgage value is removed:
+      new_grant_value = sales_log.grant + sales_log.mortgage
+      sales_log.update!(mortgageused: 2, grant: new_grant_value)
+      sales_log.update!(mortgageused: 1)
+      record_from_db = ActiveRecord::Base.connection.execute("select mortgage from sales_logs where id=#{sales_log.id}").to_a[0]
+      expect(record_from_db["mortgage"]).to eq(nil)
+    end
+
     context "when outright sale and buyers will live in the property" do
       let(:sales_log) { create(:sales_log, :outright_sale_setup_complete, buylivein: 1, jointpur:) }