Can only update a competition's currency code if there are no unrefunded payments

app/models/competition.rb

@@ -353,6 +353,12 @@ def advancement_condition_must_be_present_for_all_non_final_rounds
     end
   end
 
+  validate :payments_nil_to_change_currency
+  private def payments_nil_to_change_currency
+    return unless currency_code_changed?
+    errors.add(:currency_code, I18n.t('competitions.errors.currency_cant_change')) if total_payment_amount != 0
+  end
+
   def has_any_round_per_event?
     competition_events.map(&:rounds).none?(&:empty?)
   end
@@ -2688,6 +2694,10 @@ def disconnect_all_payment_integrations
     competition_payment_integrations.destroy_all
   end
 
+  def total_payment_amount
+    registrations.joins(:registration_payments).sum('registration_payments.amount_lowest_denomination')
+  end
+
   # Our React date picker unfortunately behaves weirdly in terms of backend data
   def self.date_json_schema(string_format)
     {

config/locales/en.yml

@@ -1933,6 +1933,7 @@ en:
         -6002: "You need to finish your registration before you can pay"
     #context: and when an error occured
     errors:
+      currency_cant_change: "You cannot change the currency until all outstanding payments have been refunded."
       invalid_name_message: "must end with a year and must contain only alphanumeric characters, dashes(-), ampersands(&), periods(.), colons(:), apostrophes('), and spaces( )"
       cannot_manage: "Cannot manage competition."
       cannot_delete_public: "Cannot delete a competition that is publicly visible."