module Gitlab
  module CurrentSettings
    extend self

    def current_application_settings
      if RequestStore.active?
        RequestStore.fetch(:current_application_settings) { ensure_application_settings! }
      else
        ensure_application_settings!
      end
    end

    delegate :sidekiq_throttling_enabled?, to: :current_application_settings

    def fake_application_settings(defaults = ::ApplicationSetting.defaults)
      FakeApplicationSettings.new(defaults)
    end

    private

    def ensure_application_settings!
      return in_memory_application_settings if ENV['IN_MEMORY_APPLICATION_SETTINGS'] == 'true'

      cached_application_settings || uncached_application_settings
    end

    def cached_application_settings
      begin
        ::ApplicationSetting.cached
      rescue ::Redis::BaseError, ::Errno::ENOENT, ::Errno::EADDRNOTAVAIL
        # In case Redis isn't running or the Redis UNIX socket file is not available
      end
    end

    def uncached_application_settings
      return fake_application_settings unless connect_to_db?

      db_settings = ::ApplicationSetting.current

      # If there are pending migrations, it's possible there are columns that
      # need to be added to the application settings. To prevent Rake tasks
      # and other callers from failing, use any loaded settings and return
      # defaults for missing columns.
      if ActiveRecord::Migrator.needs_migration?
        defaults = ::ApplicationSetting.defaults
        defaults.merge!(db_settings.attributes.symbolize_keys) if db_settings.present?
        return fake_application_settings(defaults)
      end

      return db_settings if db_settings.present?

      ::ApplicationSetting.create_from_defaults || in_memory_application_settings
    end

    def in_memory_application_settings
      @in_memory_application_settings ||= ::ApplicationSetting.new(::ApplicationSetting.defaults) # rubocop:disable Gitlab/ModuleWithInstanceVariables
    rescue ActiveRecord::StatementInvalid, ActiveRecord::UnknownAttributeError
      # In case migrations the application_settings table is not created yet,
      # we fallback to a simple OpenStruct
      fake_application_settings
    end

    def connect_to_db?
      # When the DBMS is not available, an exception (e.g. PG::ConnectionBad) is raised
      active_db_connection = ActiveRecord::Base.connection.active? rescue false

      active_db_connection &&
        ActiveRecord::Base.connection.table_exists?('application_settings')
    rescue ActiveRecord::NoDatabaseError
      false
    end
  end
end