module ActionCable
  module Channel
    module PeriodicTimers
      extend ActiveSupport::Concern

      included do
        class_attribute :periodic_timers, instance_reader: false
        self.periodic_timers = []

        after_subscribe   :start_periodic_timers
        after_unsubscribe :stop_periodic_timers
      end

      module ClassMethods
        # Allow you to call a private method <tt>every</tt> so often seconds. This periodic timer can be useful
        # for sending a steady flow of updates to a client based off an object that was configured on subscription.
        # It's an alternative to using streams if the channel is able to do the work internally.
        def periodically(callback, every:)
          self.periodic_timers += [ [ callback, every: every ] ]
        end
      end

      private
        def active_periodic_timers
          @active_periodic_timers ||= []
        end

        def start_periodic_timers
          self.class.periodic_timers.each do |callback, options|
            active_periodic_timers << EventMachine::PeriodicTimer.new(options[:every]) do
              connection.worker_pool.async_run_periodic_timer(self, callback)
            end
          end
        end

        def stop_periodic_timers
          active_periodic_timers.each { |timer| timer.cancel }
        end
    end
  end
end