# 模組

## 何謂模組：
1. 任何希望表現得像鴨子類型並且有做角色扮演的物件都可以使用它
2. 可以定義一組被命名的方法，這些方法獨立於類別，並且可以混入到任何物件

## 一個物件可回應的所有訊息包括有:
* 自身實作的訊息
* 所有上游物件所實作的訊息
* 被包含的模組所實作的訊息
* 所有上游物件包含的模組所實作的訊息


class Schedule
  attr_accessor :lead_days
  def initialize; end

  def scheduled?(target, _starting, _ending)
    if target.class == Bicycle
      lead_days = 1
    elsif target.class == Mechanic
      lead_days = 4
    elsif target.class == Vehicle
      lead_days = 3
    end
  end

  def add(target, starting, ending); end

  def remove(target, starting, ending); end
end


class Bicycle
  attr_accessor :lead_days
  def initialize
      @lead_days = 1
  end
end

class Schedule
  def initialize; end

  def scheduled?(target, _starting, _ending)
    target.lead_days
    # 可以實作lead_days則為Schedulable
  end

  def add(target, starting, ending); end

  def remove(target, starting, ending); end
end

### 以訊息角度思考

bicycle = Bicycle.new
Schedule.new.scheduled?(bicycle, starting, ending)

如果你對B物件(bicycle)感興趣，那麼你不應該被迫知道A(Schedule)物件。即使你只是使用它來尋找關於B物件的事情，也不應該這樣做。

**應為**

bicycle.scheduled?(starting, ending)

**重構**

class Schedule
  def schedule?
      false
  end
end

class Bicycle
  attr_reader :schedule, ...
  def initialize(args = {})
      @schedule = args[:schedule] || Schedule.new
  end
    
  def schedulable?(start_date, end_date)
      !scheduled?(start_date-lead_days, end_date)
  end
    
  def scheduled?(start_date, end_date)
      schedule.scheduled?(self, start_date, end_date)
  end
    
  def lead_days
      1
  end
end

### Mechanic和Vehicle也都會扮演這個角色 -> DRY

module Scheulable
    attr_writer :schedule
    
  def schedule
    @schedule || = ::Schedule.new
  end
    
  def schdeuled?(start_date, end_date)
    schedule.scheduled?(self, start_date, end_date)
  end
    
  def schedulable?(start_date, end_date)
    !scheduled?(start_date-lead_days, end_date)
  end
    
  def lead_days
    0 #默認值
  end
end



## 結論：
1. 里氏代替原則(Liskov Substitution Principle，LSP )
2. 範本方法模式(Template method pattern)