Rename user cohorts -> cohorts

1 files changed, 87 insertions, 0 deletions

diff --git a/app/services/cohorts_service.rb b/app/services/cohorts_service.rb
new file mode 100644
index 00000000000..e7f8a50605f
--- /dev/null
+++ b/app/services/cohorts_service.rb
@@ -0,0 +1,87 @@
+class CohortsService
+  MONTHS_INCLUDED = 12
+
+  # Get a hash that looks like:
+  #
+  #     {
+  #       month => {
+  #         months: [3, 2, 1],
+  #         total: 3
+  #         inactive: 0
+  #      },
+  #      etc.
+  #
+  # The `months` array is always from oldest to newest, so it's always
+  # non-strictly decreasing from left to right.
+  #
+  def execute
+    cohorts = {}
+    months = Array.new(MONTHS_INCLUDED) { |i| i.months.ago.beginning_of_month.to_date }
+
+    MONTHS_INCLUDED.times do
+      created_at_month = months.last
+      activity_months = running_totals(months, created_at_month)
+
+      # Even if no users registered in this month, we always want to have a
+      # value to fill in the table.
+      inactive = counts_by_month[[created_at_month, nil]].to_i
+
+      cohorts[created_at_month] = {
+        months: activity_months,
+        total: activity_months.first,
+        inactive: inactive
+      }
+
+      months.pop
+    end
+
+    cohorts
+  end
+
+  private
+
+  # Calculate a running sum of active users, so users active in later months
+  # count as active in this month, too. Start with the most recent month first,
+  # for calculating the running totals, and then reverse for displaying in the
+  # table.
+  def running_totals(all_months, created_at_month)
+    all_months
+      .map { |activity_month| counts_by_month[[created_at_month, activity_month]] }
+      .reduce([]) { |result, total| result << result.last.to_i + total.to_i }
+      .reverse
+  end
+
+  # Get a hash that looks like:
+  #
+  #     {
+  #       [created_at_month, current_sign_in_at_month] => count,
+  #       [created_at_month, current_sign_in_at_month_2] => count_2,
+  #       # etc.
+  #     }
+  #
+  # created_at_month can never be nil, but current_sign_in_at_month can (when a
+  # user has never logged in, just been created). This covers the last twelve
+  # months.
+  #
+  def counts_by_month
+    @counts_by_month ||=
+      begin
+        created_at_month = column_to_date('created_at')
+        current_sign_in_at_month = column_to_date('current_sign_in_at')
+
+        User
+          .where('created_at > ?', MONTHS_INCLUDED.months.ago.end_of_month)
+          .group(created_at_month, current_sign_in_at_month)
+          .reorder("#{created_at_month} ASC", "#{current_sign_in_at_month} ASC")
+          .count
+      end
+  end
+
+  def column_to_date(column)
+    if Gitlab::Database.postgresql?
+      "CAST(DATE_TRUNC('month', #{column}) AS date)"
+    elsif Gitlab::Database.mysql?
+      "STR_TO_DATE(DATE_FORMAT(#{column}, '%Y-%m-01'), '%Y-%m-%d')"
+    end
+  end
+end