使用两个状态机的Split ActiveRecord模型

我有一个使用两个的模型 state machines

class MyModel < ActiveRecord::Base

  state_machine :call_state, :initial => :pending do
    event :start do
      transition :pending => :started
    end

    event :restart do
      transition :started => :pending
    end

    event :finish do
      transition :started => :finished
    end
  end

  state_machine :payment_state, :initial => :unpaid  do
    event :pay do
      transition :unpaid => :paid
    end

    event :pay_back do
      transition :paid => :paid_back
    end

    event :reject_payment do
      transition :unpaid => :rejected
    end
  end

  #tons of methods related with call_state
  #tons of methods related with payment_state
end

我想把这个分开 ActiveRecord 三个模型:

1. 要封装的模块/类 定义和方法 与相关的 call_state
2. 要封装的模块/类 定义和方法 与相关的 payment_state

3. 模块/类 与两者一起工作 。第三个模块/类可以有如下方法

   def can_call?
     xxx.paid? and yyy.can_start?
   end
   

哪里 xxx / yyy 可能是 MyModel 实例或包装类中的方法。我不知道。。。

问题是: 最好的方法是什么?