move collection year method

app/models/lettings_log.rb

@@ -77,14 +77,6 @@ class LettingsLog < Log
     FormHandler.instance.get_form(form_name) || FormHandler.instance.forms.first.second
   end
 
-  def collection_start_year
-    return @start_year if @start_year
-    return unless startdate
-
-    window_end_date = Time.zone.local(startdate.year, 4, 1)
-    @start_year = startdate < window_end_date ? startdate.year - 1 : startdate.year
-  end
-
   def recalculate_start_year!
     @start_year = nil
     collection_start_year

app/models/log.rb

@@ -5,6 +5,14 @@ class Log < ApplicationRecord
   belongs_to :managing_organisation, class_name: "Organisation", optional: true
   belongs_to :created_by, class_name: "User", optional: true
 
+  def collection_start_year
+    return @start_year if @start_year
+    return unless startdate
+
+    window_end_date = Time.zone.local(startdate.year, 4, 1)
+    @start_year = startdate < window_end_date ? startdate.year - 1 : startdate.year
+  end
+
 private
 
   def update_status!

app/models/sales_log.rb

@@ -13,6 +13,10 @@ class SalesLog < Log
   STATUS = { "not_started" => 0, "in_progress" => 1, "completed" => 2 }.freeze
   enum status: STATUS
 
+  def startdate
+    saledate
+  end
+
   def self.editable_fields
     attribute_names
   end
@@ -23,14 +27,6 @@ class SalesLog < Log
     "#{collection_start_year}_#{collection_start_year + 1}_sales"
   end
 
-  def collection_start_year
-    return @sale_year if @sale_year
-    return unless saledate
-
-    window_end_date = Time.zone.local(saledate.year, 4, 1)
-    @sale_year = saledate < window_end_date ? saledate.year - 1 : saledate.year
-  end
-
   def form
     FormHandler.instance.get_form(form_name) || FormHandler.instance.get_form("2022_2023_sales")
   end