create the SalesLogCsvService

create a necessary method on the log to enable submission method to be included on the csv
derive values for the two halves of previous postcode for export

app/models/derived_variables/sales_log_variables.rb

@@ -18,6 +18,7 @@ module DerivedVariables::SalesLogVariables
     end
     self.deposit = value if outright_sale? && mortgage_not_used?
     self.pcode1, self.pcode2 = postcode_full.split(" ") if postcode_full.present?
+    self.ppostc1, self.ppostc2 = postcode_full.split(" ") if ppostcode_full.present?
     self.totchild = total_child
     self.totadult = total_adult + total_elder
     self.hhmemb = number_of_household_members

app/models/log.rb

@@ -136,6 +136,16 @@ class Log < ApplicationRecord
     format_as_currency(field_value)
   end
 
+  def creation_method
+    if bulk_upload_id.present?
+      "bulk upload"
+    elsif old_id.present?
+      "migrated"
+    else
+      "single log"
+    end
+  end
+
 private
 
   # Handle logs that are older than previous collection start date

app/services/csv/sales_log_csv_service.rb

@@ -0,0 +1,87 @@
+module Csv
+  class SalesLogCsvService
+    def initialize(export_type:)
+      @export_type = export_type
+      @attributes = sales_log_attributes
+    end
+
+    def prepare_csv(logs)
+      CSV.generate(headers: true) do |csv|
+        csv << @attributes
+
+        logs.find_each do |log|
+          csv << @attributes.map { |attribute| value(attribute, log) }
+        end
+      end
+    end
+
+  private
+
+    ATTRIBUTES_OF_RELATED_OBJECTS = {
+      created_by_name: %i[created_by name],
+      is_dpo: %i[created_by is_dpo],
+      owning_organisation_name: %i[owning_organisation name],
+    }
+
+    # can this be made so general it can also be extracted? quite possibly
+    def value(attribute, log)
+      if ATTRIBUTES_OF_RELATED_OBJECTS.key? attribute.to_sym
+        call_chain = ATTRIBUTES_OF_RELATED_OBJECTS[attribute.to_sym]
+        call_chain.reduce(log) { |object, next_call| object&.public_send(next_call) }
+      elsif %w[la prevloc].include? attribute # for all exports we output both the codes and labels for these location attributes
+        log.send(attribute)
+      elsif %w[la_label prevloc_label].include? attribute # as above
+        attribute = attribute.remove("_label")
+        field_value = log.send(attribute)
+        get_label(field_value, attribute, log)
+      else
+        value = log.public_send(attribute)
+        case @export_type
+        when "codes"
+          value
+        when "labels"
+          answer_label = get_label(value, attribute, log)
+          answer_label || label_if_boolean_value(value) || value
+        end
+      end
+    end
+
+    # extract - common to lettings log csv service
+    def get_label(value, attribute, log)
+      log.form
+         .get_question(attribute, log)
+         &.label_from_value(value)
+    end
+
+    # also extract
+    def label_if_boolean_value(value)
+      return "Yes" if value == true
+      return "No" if value == false
+    end
+
+    ATTRIBUTE_MAPPINGS = {
+      "exdate" => %w[exday exmonth exyear],
+      "hodate" => %w[hoday homonth hoyear],
+      "postcode_full" => %w[pcode1 pcode2],
+      "ppostcode_full" => %w[ppostc1 ppostc2],
+      "la" => %w[la la_label],
+      "prevloc" => %w[prevloc prevloc_label],
+    }
+
+    def sales_log_attributes
+      ordered_questions = FormHandler.instance.ordered_sales_questions_for_all_years
+      ordered_questions.reject! { |q| q.id.match?(/((?<!la)_known)|(_value_check)/) }
+      attributes = ordered_questions.flat_map do |question|
+        if question.type == "checkbox"
+          question.answer_options.keys
+        elsif ATTRIBUTE_MAPPINGS.key? question.id
+          ATTRIBUTE_MAPPINGS[question.id]
+        else
+          question.id
+        end
+      end
+      non_question_fields = %w[id status created_at updated_at created_by_name is_dpo owning_organisation_name collection_start_year creation_method]
+      attributes = non_question_fields + attributes
+    end
+  end
+end