1 files changed, 93 insertions, 0 deletions
diff --git a/lib/gitlab/experimentation.rb b/lib/gitlab/experimentation.rb
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+++ b/lib/gitlab/experimentation.rb
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+# frozen_string_literal: true
+
+# == Experimentation
+#
+# Utility module used for A/B testing experimental features. Define your experiments in the `EXPERIMENTS` constant.
+# The feature_toggle and environment keys are optional. If the feature_toggle is not set, a feature with the name of
+# the experiment will be checked, with a default value of true. The enabled_ratio is required and should be
+# the ratio for the number of users for which this experiment is enabled. For example: a ratio of 0.1 will
+# enable the experiment for 10% of the users (determined by the `experimentation_subject_index`).
+#
+module Gitlab
+  module Experimentation
+    EXPERIMENTS = {
+      signup_flow: {
+        feature_toggle: :experimental_separate_sign_up_flow,
+        environment: ::Gitlab.dev_env_or_com?,
+        enabled_ratio: 0.1
+      }
+    }.freeze
+
+    # 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.
+    #
+    module ControllerConcern
+      extend ActiveSupport::Concern
+
+      included do
+        before_action :set_experimentation_subject_id_cookie
+        helper_method :experiment_enabled?
+      end
+
+      def set_experimentation_subject_id_cookie
+        return if cookies[:experimentation_subject_id].present?
+
+        cookies.permanent.signed[:experimentation_subject_id] = {
+          value: SecureRandom.uuid,
+          domain: :all,
+          secure: ::Gitlab.config.gitlab.https
+        }
+      end
+
+      def experiment_enabled?(experiment_key)
+        Experimentation.enabled?(experiment_key, experimentation_subject_index)
+      end
+
+      private
+
+      def experimentation_subject_index
+        experimentation_subject_id = cookies.signed[:experimentation_subject_id]
+        return if experimentation_subject_id.blank?
+
+        experimentation_subject_id.delete('-').hex % 100
+      end
+    end
+
+    class << self
+      def experiment(key)
+        Experiment.new(EXPERIMENTS[key].merge(key: key))
+      end
+
+      def enabled?(experiment_key, experimentation_subject_index)
+        return false unless EXPERIMENTS.key?(experiment_key)
+
+        experiment = experiment(experiment_key)
+
+        experiment.feature_toggle_enabled? &&
+          experiment.enabled_for_environment? &&
+          experiment.enabled_for_experimentation_subject?(experimentation_subject_index)
+      end
+    end
+
+    Experiment = Struct.new(:key, :feature_toggle, :environment, :enabled_ratio, keyword_init: true) do
+      def feature_toggle_enabled?
+        return Feature.enabled?(key, default_enabled: true) if feature_toggle.nil?
+
+        Feature.enabled?(feature_toggle)
+      end
+
+      def enabled_for_environment?
+        return true if environment.nil?
+
+        environment
+      end
+
+      def enabled_for_experimentation_subject?(experimentation_subject_index)
+        return false if enabled_ratio.nil? || experimentation_subject_index.blank?
+
+        experimentation_subject_index <= enabled_ratio * 100
+      end
+    end
+  end
+end