module EventSourcing

  module EventPublisher

    @@subscribers=[]

    def self.add_subscriber(subscriber)
      @@subscribers << subscriber
    end

    def self.delete_subscriber(subscripber)
      @@subscribers.delete(subscriber)
    end

    def self.get_subscribers
      @@subscribers
    end

    def self.publish(event)
      @@subscribers.each do |subscriber|
        subscriber.handle(event) if subscriber.is_subscribet_to? event
      end
    end

  end

  module AggregateRoot

    def initialize
      @events = []
      super()
    end

    def save
      # Persist the entity
      publish_events
      clear_events
    end

    def publish_events()
      @events.each do |event|
        EventSourcing::EventPublisher.publish(event)
      end
    end

    private
      def record_event(event)
        @events << event
      end

      def clear_events
        @events = []
      end

  end

end

class Employee

  include EventSourcing::AggregateRoot

  attr_reader :name, :title
  attr_reader :salary

  def initialize( name, title, salary)
    super()
    @name = name
    @title = title
    @salary = salary
  end

  def salary=(new_salary)
    @salary = new_salary
    record_event( SalaryHasChangedEvent.new(self) )
  end
end


class SalaryHasChangedEvent

  attr_reader :employee

  def initialize(employee)
    @employee = employee
  end
end

class CongratulateEmployeeSubscriber

  def is_subscribet_to?(event)
    event.class == SalaryHasChangedEvent
  end

  def handle(event)
    puts "Cogratulations #{event.employee.name}!!!!"
  end

end

EventSourcing::EventPublisher.add_subscriber(CongratulateEmployeeSubscriber.new)

fred = Employee.new("Fred Flintstone", "Crane Operator", 30000.0)
fred.salary=35000.0
fred.save

barney = Employee.new("Barney Rubble", "Crane Operator", 10000.0)
barney.save