canvas-lms/lib/feature.rb

#
# Copyright (C) 2013 - present Instructure, Inc.
#
# This file is part of Canvas.
#
# Canvas is free software: you can redistribute it and/or modify it under
# the terms of the GNU Affero General Public License as published by the Free
# Software Foundation, version 3 of the License.
#
# Canvas is distributed in the hope that it will be useful, but WITHOUT ANY
# WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
# A PARTICULAR PURPOSE. See the GNU Affero General Public License for more
# details.
#
# You should have received a copy of the GNU Affero General Public License along
# with this program. If not, see <http://www.gnu.org/licenses/>.
#

class Feature
  ATTRS = [:feature, :display_name, :description, :applies_to, :state,
           :root_opt_in, :enable_at, :beta,
           :release_notes_url, :custom_transition_proc, :visible_on,
           :after_state_change_proc, :autoexpand, :touch_context].freeze
  attr_reader *ATTRS

  def initialize(opts = {})
    @state = 'allowed'
    opts.each do |key, val|
      next unless ATTRS.include?(key)
      next if key == :state && !%w(hidden off allowed on).include?(val)
      instance_variable_set "@#{key}", val
    end
    # for RootAccount features, "allowed" state is redundant; show "off" instead
    @root_opt_in = true if @applies_to == 'RootAccount'
  end

  def clone_for_cache
    Feature.new(feature: @feature, state: @state)
  end

  def default?
    true
  end

  def locked?(query_context)
    query_context.blank? || !allowed? && !hidden?
  end

  def enabled?
    @state == 'on'
  end

  def allowed?
    @state == 'allowed'
  end

  def hidden?
    @state == 'hidden'
  end

  def self.environment
    if Rails.env.development?
      :development
    elsif Rails.env.test?
      :ci
    elsif ApplicationController.test_cluster_name == 'beta'
      :beta
    elsif ApplicationController.test_cluster_name == 'test'
      :test
    else
      :production
    end
  end

  def self.production_environment?
    self.environment == :production
  end

  # Register one or more features.  Must be done during application initialization.
  # NOTE: there is refactoring going on for feature flags: ADMIN-2538
  #       if you need to add/modify/delete a FF, they have been moved to ./lib/feature_flags/*yml
  # The feature_hash is as follows:
  #   automatic_essay_grading: {
  #     display_name: -> { I18n.t('features.automatic_essay_grading', 'Automatic Essay Grading') },
  #     description: -> { I18n.t('features.automatic_essay_grading_description, 'Popup text describing the feature goes here') },
  #     applies_to: 'Course', # or 'RootAccount' or 'Account' or 'User'
  #     state: 'allowed',     # or 'on', 'hidden', or 'disabled'
  #                           # - 'hidden' means the feature must be set by a site admin before it will be visible
  #                           #   (in that context and below) to other users
  #                           # - 'disabled' means the feature will not appear in the feature list and
  #                           #   cannot be turned on. It is intended for use in environment state overrides.
  #     root_opt_in: false,   # if true, 'allowed' features in source or site admin
  #                           # will be inherited in "off" state by root accounts
  #     enable_at: Date.new(2014, 1, 1),  # estimated release date shown in UI
  #     beta: false,          # 'beta' tag shown in UI
  #     release_notes_url: 'http://example.com/',
  #
  #     # allow overriding feature definitions on a per-environment basis
  #     # valid environments are development, production, beta, test, ci
  #     environments: {
  #       production: {
  #         state: 'disabled'
  #       }
  #     }
  #
  #     # optional: you can supply a Proc to attach warning messages to and/or forbid certain transitions
  #     # see lib/feature/draft_state.rb for example usage
  #     custom_transition_proc: ->(user, context, from_state, transitions) do
  #       if from_state == 'off' && context.is_a?(Course) && context.has_submitted_essays?
  #         transitions['on']['warning'] = I18n.t('features.automatic_essay_grading.enable_warning',
  #           'Enabling this feature after some students have submitted essays may yield inconsistent grades.')
  #       end
  #     end,
  #
  #     # optional hook to be called before after a feature flag change
  #     # queue a delayed_job to perform any nontrivial processing
  #     after_state_change_proc:  ->(user, context, old_state, new_state) { ... }
  #   }
  VALID_STATES = %w(on allowed hidden disabled).freeze
  VALID_APPLIES_TO = %w(Course Account RootAccount User SiteAdmin).freeze
  VALID_ENVS = %i(development ci beta test production).freeze

  DISABLED_FEATURE = Feature.new.freeze

  def self.register(feature_hash)
    @features ||= {}
    feature_hash.each do |feature_name, attrs|
      apply_environment_overrides!(feature_name, attrs)
      feature = feature_name.to_s
      validate_attrs(attrs, feature)
      if attrs[:state] == 'disabled'
        @features[feature] = DISABLED_FEATURE
      else
        @features[feature] = Feature.new({ feature: feature }.merge(attrs))
      end
    end
  end

  def self.validate_attrs(attrs, feature)
    raise "state is required for feature #{feature}" unless attrs[:state]
    raise "applies_to is required for feature #{feature}" unless attrs[:applies_to]
    raise "invalid 'state' for feature #{feature}: must be one of #{VALID_STATES}, is #{attrs[:state]}" unless VALID_STATES.include? attrs[:state]
    raise "invalid 'applies_to' for feature #{feature}: must  be one of #{VALID_APPLIES_TO}, is #{attrs[:applies_to]}" unless VALID_APPLIES_TO.include? attrs[:applies_to]
  end

  def self.definitions
    @features ||= {}
    @features.freeze unless @features.frozen?
    @features
  end

  def self.apply_environment_overrides!(feature_name, feature_hash)
    environments = feature_hash.delete(:environments)
    if environments
      raise "invalid environment tag for feature #{feature_name}: must be one of #{VALID_ENVS}" unless (environments.keys - VALID_ENVS).empty?
      env = self.environment
      if environments.key?(env)
        feature_hash.merge!(environments[env])
      end
    end
  end

  def applies_to_object(object)
    case @applies_to
    when 'SiteAdmin'
      object.is_a?(Account) && object.site_admin?
    when 'RootAccount'
      object.is_a?(Account) && object.root_account?
    when 'Account'
      object.is_a?(Account)
    when 'Course'
      object.is_a?(Course) || object.is_a?(Account)
    when 'User'
      object.is_a?(User) || object.is_a?(Account) && object.site_admin?
    else
      false
    end
  end

  def self.exists?(feature)
    definitions.key?(feature.to_s)
  end

  def self.feature_applies_to_object(feature, object)
    feature_def = definitions[feature.to_s]
    return false unless feature_def
    feature_def.applies_to_object(object)
  end

  def self.applicable_features(object)
    applicable_types = []
    if object.is_a?(Account)
      applicable_types << 'Account'
      applicable_types << 'Course'
      applicable_types << 'RootAccount' if object.root_account?
      applicable_types << 'User' if object.site_admin?
      applicable_types << 'SiteAdmin' if object.site_admin?
    elsif object.is_a?(Course)
      applicable_types << 'Course'
    elsif object.is_a?(User)
      applicable_types << 'User'
    end
    definitions.values.select { |fd| applicable_types.include?(fd.applies_to) }
  end

  def default_transitions(context, orig_state)
    valid_states = %w(off on)
    valid_states << 'allowed' if context.is_a?(Account)
    (valid_states - [orig_state]).inject({}) do |transitions, state|
      transitions[state] = { 'locked' => (state == 'allowed' && (@applies_to == 'RootAccount' &&
        context.is_a?(Account) && context.root_account? && !context.site_admin? || @applies_to == "SiteAdmin")) }
      transitions
    end
  end

  def transitions(user, context, orig_state)
    h = default_transitions(context, orig_state)
    if @custom_transition_proc.is_a?(Proc)
      @custom_transition_proc.call(user, context, orig_state, h)
    end
    h
  end

  def self.transitions(feature_name, user, context, orig_state)
    fd = definitions[feature_name.to_s]
    return nil unless fd
    fd.transitions(user, context, orig_state)
  end

  def self.remove_obsolete_flags
    valid_features = self.definitions.keys
    cutoff = Setting.get('obsolete_feature_flag_cutoff_days', 60).to_i.days.ago
    delete_scope = FeatureFlag.where('updated_at<?', cutoff).where.not(feature: valid_features)
    while delete_scope.limit(1000).delete_all > 0; end
  end
end

FeatureFlags::Loader.load_feature_flags