CLDC-2684 Keep fewer logs in memory when running exports (#1859)

* Keep fewer logs in memory

* refactor write_export_archive to only hold MAX_XML_RECORDS in memory at a time

app/services/exports/lettings_log_export_service.rb

@@ -10,14 +10,12 @@ module Exports
 
     def export_xml_lettings_logs(full_update: false)
       start_time = Time.zone.now
-      logs_by_collection = retrieve_lettings_logs(start_time, full_update).group_by(&:collection_start_year)
       daily_run_number = get_daily_run_number
       archives_for_manifest = {}
       base_number = LogsExport.where(empty_export: false).maximum(:base_number) || 1
       available_collection_years.each do |collection|
-        lettings_logs = logs_by_collection.fetch(collection, LettingsLog.none)
         export = build_export_run(collection, start_time, base_number, full_update)
-        archives = write_export_archive(export, lettings_logs)
+        archives = write_export_archive(export, collection, start_time, full_update)
 
         archives_for_manifest.merge!(archives)
 
@@ -65,51 +63,50 @@ module Exports
       @storage_service.write_file(file_path, string_io)
     end
 
-    def get_archive_name(lettings_log, base_number, increment)
-      return unless lettings_log.startdate
+    def get_archive_name(collection, base_number, increment)
+      return unless collection
 
-      collection_start = lettings_log.collection_start_year
-      start_month = collection_start_date(lettings_log.startdate).strftime("%b")
-      end_month = collection_end_date(lettings_log.startdate).strftime("%b")
       base_number_str = "f#{base_number.to_s.rjust(4, '0')}"
       increment_str = "inc#{increment.to_s.rjust(4, '0')}"
-      "core_#{collection_start}_#{collection_start + 1}_#{start_month}_#{end_month}_#{base_number_str}_#{increment_str}".downcase
+      "core_#{collection}_#{collection + 1}_apr_mar_#{base_number_str}_#{increment_str}".downcase
     end
 
-    def write_export_archive(export, lettings_logs)
+    def write_export_archive(export, collection, start_time, full_update)
       @logger.info("Writing export archives")
-      # Order lettings logs per archive
-      lettings_logs_per_archive = {}
-      lettings_logs.each do |lettings_log|
-        archive = get_archive_name(lettings_log, export.base_number, export.increment_number)
-        next unless archive
+      archive = get_archive_name(collection, export.base_number, export.increment_number) # archive name would be the same for all logs because they're already filtered by year (?)
 
-        if lettings_logs_per_archive.key?(archive)
-          lettings_logs_per_archive[archive] << lettings_log
-        else
-          lettings_logs_per_archive[archive] = [lettings_log]
-        end
-      end
+      # Write archive
+      logs_count = retrieve_lettings_logs(start_time, full_update).filter_by_year(collection).count
+      @logger.info("Writing #{archive} - #{logs_count} logs")
+      manifest_xml = build_manifest_xml(logs_count)
+      return {} if logs_count.zero?
 
-      # Write all archives
-      archive_datetimes = {}
-      @logger.info("Following archives to write:")
-      # rubocop:disable Style/CombinableLoops
-      lettings_logs_per_archive.each do |archive, lettings_logs_to_export|
-        @logger.info("#{archive} - #{lettings_logs_to_export.count} logs")
-      end
-      lettings_logs_per_archive.each do |archive, lettings_logs_to_export|
-        manifest_xml = build_manifest_xml(lettings_logs_to_export.count)
       zip_file = Zip::File.open_buffer(StringIO.new)
       zip_file.add("manifest.xml", manifest_xml)
 
       part_number = 1
-        lettings_logs_to_export.each_slice(MAX_XML_RECORDS) do |lettings_logs_slice|
+      last_processed_marker = nil
+
+      loop do
+        lettings_logs_slice = if last_processed_marker.present?
+                                retrieve_lettings_logs(start_time, full_update).filter_by_year(collection)
+                                      .where("created_at > ?", last_processed_marker)
+                                      .order(:created_at)
+                                      .limit(MAX_XML_RECORDS)
+                              else
+                                retrieve_lettings_logs(start_time, full_update).filter_by_year(collection)
+                                .order(:created_at)
+                                .limit(MAX_XML_RECORDS)
+                              end
+
+        break if lettings_logs_slice.empty?
+
         data_xml = build_export_xml(lettings_logs_slice)
         part_number_str = "pt#{part_number.to_s.rjust(3, '0')}"
         @logger.info("Adding #{archive}_#{part_number_str}.xml")
         zip_file.add("#{archive}_#{part_number_str}.xml", data_xml)
         part_number += 1
+        last_processed_marker = lettings_logs_slice.last.created_at
       end
 
       # Required by S3 to avoid Aws::S3::Errors::BadDigest
@@ -117,11 +114,7 @@ module Exports
       zip_io.rewind
       @logger.info("Writting #{archive}.zip")
       @storage_service.write_file("#{archive}.zip", zip_io)
-        archive_datetimes[archive] = Time.zone.now
-      end
-      # rubocop:enable Style/CombinableLoops
-
-      archive_datetimes
+      { archive => Time.zone.now }
     end
 
     def retrieve_lettings_logs(start_time, full_update)