1 files changed, 116 insertions, 0 deletions
diff --git a/lib/gitlab/analytics/cycle_analytics/aggregated/records_fetcher.rb b/lib/gitlab/analytics/cycle_analytics/aggregated/records_fetcher.rb
new file mode 100644
index 00000000000..7dce757cdc8
--- /dev/null
+++ b/lib/gitlab/analytics/cycle_analytics/aggregated/records_fetcher.rb
@@ -0,0 +1,116 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module Analytics
+    module CycleAnalytics
+      module Aggregated
+        class RecordsFetcher
+          include Gitlab::Utils::StrongMemoize
+          include StageQueryHelpers
+
+          MAX_RECORDS = 20
+
+          MAPPINGS = {
+            Issue => {
+              serializer_class: AnalyticsIssueSerializer,
+              includes_for_query: { project: { namespace: [:route] }, author: [] },
+              columns_for_select: %I[title iid id created_at author_id project_id]
+            },
+            MergeRequest => {
+              serializer_class: AnalyticsMergeRequestSerializer,
+              includes_for_query: { target_project: [:namespace], author: [] },
+              columns_for_select: %I[title iid id created_at author_id state_id target_project_id]
+            }
+          }.freeze
+
+          def initialize(stage:, query:, params: {})
+            @stage = stage
+            @query = query
+            @params = params
+            @sort = params[:sort] || :end_event
+            @direction = params[:direction] || :desc
+            @page = params[:page] || 1
+            @per_page = MAX_RECORDS
+            @stage_event_model = query.model
+          end
+
+          def serialized_records
+            strong_memoize(:serialized_records) do
+              records = ordered_and_limited_query.select(stage_event_model.arel_table[Arel.star], duration.as('total_time'))
+
+              yield records if block_given?
+              issuables_and_records = load_issuables(records)
+
+              preload_associations(issuables_and_records.map(&:first))
+
+              issuables_and_records.map do |issuable, record|
+                project = issuable.project
+                attributes = issuable.attributes.merge({
+                  project_path: project.path,
+                  namespace_path: project.namespace.route.path,
+                  author: issuable.author,
+                  total_time: record.total_time
+                })
+                serializer.represent(attributes)
+              end
+            end
+          end
+
+          # rubocop: disable CodeReuse/ActiveRecord
+          def ordered_and_limited_query
+            sorting_options = {
+              end_event: {
+                asc: -> { query.order(end_event_timestamp: :asc) },
+                desc: -> { query.order(end_event_timestamp: :desc) }
+              },
+              duration: {
+                asc: -> { query.order(duration.asc) },
+                desc: -> { query.order(duration.desc) }
+              }
+            }
+
+            sort_lambda = sorting_options.dig(sort, direction) || sorting_options.dig(:end_event, :desc)
+
+            sort_lambda.call
+              .page(page)
+              .per(per_page)
+              .without_count
+          end
+          # rubocop: enable CodeReuse/ActiveRecord
+
+          private
+
+          attr_reader :stage, :query, :sort, :direction, :params, :page, :per_page, :stage_event_model
+
+          delegate :subject_class, to: :stage
+
+          def load_issuables(stage_event_records)
+            stage_event_records_by_issuable_id = stage_event_records.index_by(&:issuable_id)
+
+            issuable_model = stage_event_model.issuable_model
+            issuables_by_id = issuable_model.id_in(stage_event_records_by_issuable_id.keys).index_by(&:id)
+
+            stage_event_records_by_issuable_id.map do |issuable_id, record|
+              [issuables_by_id[issuable_id], record] if issuables_by_id[issuable_id]
+            end.compact
+          end
+
+          def serializer
+            MAPPINGS.fetch(subject_class).fetch(:serializer_class).new
+          end
+
+          # rubocop: disable CodeReuse/ActiveRecord
+          def preload_associations(records)
+            ActiveRecord::Associations::Preloader.new.preload(
+              records,
+              MAPPINGS.fetch(subject_class).fetch(:includes_for_query)
+            )
+
+            records
+          end
+          # rubocop: enable CodeReuse/ActiveRecord
+        end
+      end
+    end
+  end
+end