Started refactoring stuff to add events to cycle analytics

- Refactored cycle analytics class to extract DB logic
- Reuse logic in new events fetcher
- Started adding cycle analytics events class and spec (still not functional)

app/models/cycle_analytics.rb

 class CycleAnalytics
-  include Gitlab::Database::Median
-  include Gitlab::Database::DateTime
-
-  DEPLOYMENT_METRIC_STAGES = %i[production staging]
+  include Gitlab::CycleAnalytics::MetricsFetcher
 
   def initialize(project, from:)
     @project = project
@@ -56,48 +53,4 @@ class CycleAnalytics
                      Issue.arel_table[:created_at],
                      MergeRequest::Metrics.arel_table[:first_deployed_to_production_at])
   end
-
-  private
-
-  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), end_time_attrs, start_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)
-    arel_table = MergeRequestsClosingIssues.arel_table
-
-    # Load issues
-    query = arel_table.join(Issue.arel_table).on(Issue.arel_table[:id].eq(arel_table[:issue_id])).
-            join(Issue::Metrics.arel_table).on(Issue.arel_table[:id].eq(Issue::Metrics.arel_table[:issue_id])).
-            where(Issue.arel_table[:project_id].eq(@project.id)).
-            where(Issue.arel_table[:deleted_at].eq(nil)).
-            where(Issue.arel_table[:created_at].gteq(@from))
-
-    # Load merge_requests
-    query = query.join(MergeRequest.arel_table, Arel::Nodes::OuterJoin).
-            on(MergeRequest.arel_table[:id].eq(arel_table[:merge_request_id])).
-            join(MergeRequest::Metrics.arel_table).
-            on(MergeRequest.arel_table[:id].eq(MergeRequest::Metrics.arel_table[:merge_request_id]))
-
-    if DEPLOYMENT_METRIC_STAGES.include?(name)
-      # Limit to merge requests that have been deployed to production after `@from`
-      query.where(MergeRequest::Metrics.arel_table[:first_deployed_to_production_at].gteq(@from))
-    end
-
-    query
-  end
 end

lib/gitlab/cycle_analytics/events.rb

+module Gitlab
+  module CycleAnalytics
+    class Events
+      def initialize(project:, from:)
+        @project = project
+        @from = from
+        @fetcher = EventsFetcher.new(project: project, from: from)
+      end
+
+      def issue_events
+        @fetcher.fetch_issues
+      end
+    end
+  end
+end

lib/gitlab/cycle_analytics/events_fetcher.rb

+module Gitlab
+  module CycleAnalytics
+    class EventsFetcher
+      include MetricsFetcher
+
+      def initialize(project:, from:)
+        @project = project
+        @from = from
+      end
+
+      def fetch_issues
+        cte_table = Arel::Table.new("cte_table_for_issue")
+
+        interval_query = Arel::Nodes::As.new(
+          cte_table,
+          subtract_datetimes(base_query_for(:issue), *attributes, 'issue'))
+
+        #TODO ActiveRecord::Base.connection.execute(interval_query)
+      end
+
+      def attributes
+        [issue_metrics_table[:first_associated_with_milestone_at],
+         issue_metrics_table[:first_added_to_board_at]]
+      end
+    end
+  end
+end

lib/gitlab/cycle_analytics/metrics_fetcher.rb

+module Gitlab
+  module CycleAnalytics
+    module MetricsFetcher
+      include Gitlab::Database::Median
+      include Gitlab::Database::DateTime
+
+      DEPLOYMENT_METRIC_STAGES = %i[production staging]
+
+      private
+
+      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), end_time_attrs, start_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 = issue_metrics_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))
+
+        # Load merge_requests
+        query = query.join(merge_request_table, Arel::Nodes::OuterJoin).
+          on(merge_request_table[:id].eq(mr_closing_issues_table[:merge_request_id])).
+          join(merge_request_metrics_table).
+          on(merge_request_table[:id].eq(merge_request_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(merge_request_metrics_table[:first_deployed_to_production_at].gteq(@from))
+        end
+
+        query
+      end
+
+      def merge_request_metrics_table
+        MergeRequest::Metrics.arel_table
+      end
+
+      def merge_request_table
+        MergeRequest.arel_table
+      end
+
+      def mr_closing_issues_table
+        MergeRequestsClosingIssues.arel_table
+      end
+
+      def issue_table
+        Issue.arel_table
+      end
+
+      def issue_metrics_table
+        Issue::Metrics.arel_table
+      end
+    end
+  end
+end

spec/lib/gitlab/cycle_analytics/events_spec.rb

+require 'spec_helper'
+
+describe Gitlab::CycleAnalytics::Events do
+  let(:project) { create(:project) }
+  let(:from_date) { 10.days.ago }
+  let(:user) { create(:user, :admin) }
+
+  subject { described_class.new(project: project, from: from_date) }
+
+  before do
+    setup(context)
+  end
+
+  describe '#issue' do
+    let!(:context) { create(:issue, project: project) }
+
+    xit 'does something' do
+      expect(subject.issue_events).to eq([])
+    end
+  end
+
+  def setup(context)
+    create(:milestone, project: project)
+    create_merge_request_closing_issue(context)
+  end
+end