action.rb

module Scans
  class Action
    def self.call(scan)
      factory(scan).call
    end

    def self.factory(scan)
      const_get(scan.type.camelcase).new(scan)
    end

    Departure = Struct.new(:scan) do
      def call
        shipment.ship
      end

      private

      def shipment
        find_shipment_with_tracking or raise_shipment_not_found!
      end

      def find_shipment_with_tracking
        Shipment.by_tracking(scan.tracking)
      end

      def raise_shipment_not_found!
        raise NotFound.new("Departure scan for unknown tracking number")
      end
    end
  end

  class NotFound < StandardError
  end
end