2 files changed, 96 insertions, 0 deletions
diff --git a/app/services/export_csv/base_service.rb b/app/services/export_csv/base_service.rb
new file mode 100644
index 00000000000..84d44fd75fc
--- /dev/null
+++ b/app/services/export_csv/base_service.rb
@@ -0,0 +1,56 @@
+# frozen_string_literal: true
+
+module ExportCsv
+  class BaseService
+    # Target attachment size before base64 encoding
+    TARGET_FILESIZE = 15.megabytes
+
+    def initialize(relation, resource_parent, fields = [])
+      @objects = relation
+      @resource_parent = resource_parent
+      @fields = fields
+    end
+
+    def csv_data
+      csv_builder.render(TARGET_FILESIZE)
+    end
+
+    def email(user)
+      raise NotImplementedError
+    end
+
+    def invalid_fields
+      ::ExportCsv::MapExportFieldsService.new(fields, header_to_value_hash).invalid_fields
+    end
+
+    private
+
+    attr_reader :resource_parent, :objects, :fields
+
+    # rubocop: disable CodeReuse/ActiveRecord
+    def csv_builder
+      @csv_builder ||= begin
+        data_hash = MapExportFieldsService.new(fields, header_to_value_hash).execute
+
+        if preload_associations_in_batches?
+          CsvBuilder.new(objects, data_hash, associations_to_preload)
+        else
+          CsvBuilder.new(objects.preload(associations_to_preload), data_hash, [])
+        end
+      end
+    end
+    # rubocop: enable CodeReuse/ActiveRecord
+
+    def associations_to_preload
+      []
+    end
+
+    def header_to_value_hash
+      raise NotImplementedError
+    end
+
+    def preload_associations_in_batches?
+      false
+    end
+  end
+end
diff --git a/app/services/export_csv/map_export_fields_service.rb b/app/services/export_csv/map_export_fields_service.rb
new file mode 100644
index 00000000000..d4f46c65328
--- /dev/null
+++ b/app/services/export_csv/map_export_fields_service.rb
@@ -0,0 +1,40 @@
+# frozen_string_literal: true
+
+module ExportCsv
+  class MapExportFieldsService < BaseService
+    attr_reader :fields, :data
+
+    def initialize(fields, data)
+      @fields = fields
+      @data = data
+    end
+
+    def execute
+      return data if fields.empty?
+
+      selected_fields_to_hash
+    end
+
+    def invalid_fields
+      fields.reject { |field| permitted_field?(field) }
+    end
+
+    private
+
+    def selected_fields_to_hash
+      data.select { |key| requested_field?(key) }
+    end
+
+    def requested_field?(field)
+      field.downcase.in?(fields.map(&:downcase))
+    end
+
+    def permitted_field?(field)
+      field.downcase.in?(keys.map(&:downcase))
+    end
+
+    def keys
+      data.keys
+    end
+  end
+end