1 files changed, 60 insertions, 0 deletions
diff --git a/lib/gitlab/cycle_analytics/metrics_fetcher.rb b/lib/gitlab/cycle_analytics/metrics_fetcher.rb
new file mode 100644
index 00000000000..b71e8735e27
--- /dev/null
+++ b/lib/gitlab/cycle_analytics/metrics_fetcher.rb
@@ -0,0 +1,60 @@
+module Gitlab
+  module CycleAnalytics
+    class MetricsFetcher
+      include Gitlab::Database::Median
+      include Gitlab::Database::DateTime
+      include MetricsTables
+
+      DEPLOYMENT_METRIC_STAGES = %i[production staging]
+
+      def initialize(project:, from:, branch:)
+        @project = project
+        @project = project
+        @from = from
+        @branch = branch
+      end
+
+      def calculate_metric(name, start_time_attrs, end_time_attrs)
+        cte_table = Arel::Table.new("cte_table_for_#{name}")
+
+        # Build a `SELECT` query. We find the first of the `end_time_attrs` that isn't `NULL` (call this end_time).
+        # Next, we find the first of the start_time_attrs that isn't `NULL` (call this start_time).
+        # We compute the (end_time - start_time) interval, and give it an alias based on the current
+        # cycle analytics stage.
+        interval_query = Arel::Nodes::As.new(
+          cte_table,
+          subtract_datetimes(base_query_for(name), start_time_attrs, end_time_attrs, name.to_s))
+
+        median_datetime(cte_table, interval_query, name)
+      end
+
+      # Join table with a row for every <issue,merge_request> pair (where the merge request
+      # closes the given issue) with issue and merge request metrics included. The metrics
+      # are loaded with an inner join, so issues / merge requests without metrics are
+      # automatically excluded.
+      def base_query_for(name)
+        # Load issues
+        query = mr_closing_issues_table.join(issue_table).on(issue_table[:id].eq(mr_closing_issues_table[:issue_id])).
+          join(issue_metrics_table).on(issue_table[:id].eq(issue_metrics_table[:issue_id])).
+          where(issue_table[:project_id].eq(@project.id)).
+          where(issue_table[:deleted_at].eq(nil)).
+          where(issue_table[:created_at].gteq(@from))
+
+        query = query.where(build_table[:ref].eq(@branch)) if name == :test && @branch
+
+        # Load merge_requests
+        query = query.join(mr_table, Arel::Nodes::OuterJoin).
+          on(mr_table[:id].eq(mr_closing_issues_table[:merge_request_id])).
+          join(mr_metrics_table).
+          on(mr_table[:id].eq(mr_metrics_table[:merge_request_id]))
+
+        if DEPLOYMENT_METRIC_STAGES.include?(name)
+          # Limit to merge requests that have been deployed to production after `@from`
+          query.where(mr_metrics_table[:first_deployed_to_production_at].gteq(@from))
+        end
+
+        query
+      end
+    end
+  end
+end