1 files changed, 127 insertions, 0 deletions
diff --git a/lib/gitlab/experimentation/controller_concern.rb b/lib/gitlab/experimentation/controller_concern.rb
new file mode 100644
index 00000000000..c6d15d7d82d
--- /dev/null
+++ b/lib/gitlab/experimentation/controller_concern.rb
@@ -0,0 +1,127 @@
+# frozen_string_literal: true
+
+require 'zlib'
+
+# Controller concern that checks if an `experimentation_subject_id cookie` is present and sets it if absent.
+# Used for A/B testing of experimental features. Exposes the `experiment_enabled?(experiment_name)` method
+# to controllers and views. It returns true when the experiment is enabled and the user is selected as part
+# of the experimental group.
+#
+module Gitlab
+  module Experimentation
+    module ControllerConcern
+      include ::Gitlab::Experimentation::GroupTypes
+      extend ActiveSupport::Concern
+
+      included do
+        before_action :set_experimentation_subject_id_cookie, unless: :dnt_enabled?
+        helper_method :experiment_enabled?, :experiment_tracking_category_and_group
+      end
+
+      def set_experimentation_subject_id_cookie
+        return if cookies[:experimentation_subject_id].present?
+
+        cookies.permanent.signed[:experimentation_subject_id] = {
+          value: SecureRandom.uuid,
+          secure: ::Gitlab.config.gitlab.https,
+          httponly: true
+        }
+      end
+
+      def push_frontend_experiment(experiment_key)
+        var_name = experiment_key.to_s.camelize(:lower)
+        enabled = experiment_enabled?(experiment_key)
+
+        gon.push({ experiments: { var_name => enabled } }, true)
+      end
+
+      def experiment_enabled?(experiment_key)
+        return false if dnt_enabled?
+
+        return true if Experimentation.enabled_for_value?(experiment_key, experimentation_subject_index(experiment_key))
+        return true if forced_enabled?(experiment_key)
+
+        false
+      end
+
+      def track_experiment_event(experiment_key, action, value = nil)
+        return if dnt_enabled?
+
+        track_experiment_event_for(experiment_key, action, value) do |tracking_data|
+          ::Gitlab::Tracking.event(tracking_data.delete(:category), tracking_data.delete(:action), **tracking_data)
+        end
+      end
+
+      def frontend_experimentation_tracking_data(experiment_key, action, value = nil)
+        return if dnt_enabled?
+
+        track_experiment_event_for(experiment_key, action, value) do |tracking_data|
+          gon.push(tracking_data: tracking_data)
+        end
+      end
+
+      def record_experiment_user(experiment_key)
+        return if dnt_enabled?
+        return unless Experimentation.enabled?(experiment_key) && current_user
+
+        ::Experiment.add_user(experiment_key, tracking_group(experiment_key), current_user)
+      end
+
+      def experiment_tracking_category_and_group(experiment_key)
+        "#{tracking_category(experiment_key)}:#{tracking_group(experiment_key, '_group')}"
+      end
+
+      private
+
+      def dnt_enabled?
+        Gitlab::Utils.to_boolean(request.headers['DNT'])
+      end
+
+      def experimentation_subject_id
+        cookies.signed[:experimentation_subject_id]
+      end
+
+      def experimentation_subject_index(experiment_key)
+        return if experimentation_subject_id.blank?
+
+        if Experimentation.experiment(experiment_key).use_backwards_compatible_subject_index
+          experimentation_subject_id.delete('-').hex % 100
+        else
+          Zlib.crc32("#{experiment_key}#{experimentation_subject_id}") % 100
+        end
+      end
+
+      def track_experiment_event_for(experiment_key, action, value)
+        return unless Experimentation.enabled?(experiment_key)
+
+        yield experimentation_tracking_data(experiment_key, action, value)
+      end
+
+      def experimentation_tracking_data(experiment_key, action, value)
+        {
+          category: tracking_category(experiment_key),
+          action: action,
+          property: tracking_group(experiment_key, "_group"),
+          label: experimentation_subject_id,
+          value: value
+        }.compact
+      end
+
+      def tracking_category(experiment_key)
+        Experimentation.experiment(experiment_key).tracking_category
+      end
+
+      def tracking_group(experiment_key, suffix = nil)
+        return unless Experimentation.enabled?(experiment_key)
+
+        group = experiment_enabled?(experiment_key) ? GROUP_EXPERIMENTAL : GROUP_CONTROL
+
+        suffix ? "#{group}#{suffix}" : group
+      end
+
+      def forced_enabled?(experiment_key)
+        params.has_key?(:force_experiment) && params[:force_experiment] == experiment_key.to_s
+      end
+    end
+  end
+end