如果在Ruby / Rails代码块之间的其他地方重构这个

Question

Here's the code. Basically, the user selects a billing day (the 1st of each month, or the 15th of each month). The start_date is when the "contract" begins, the expire_date is when it expires.

So, if today is the 3rd, and they want to be billed on the 15th, then simply go to the 15th day of the current month. However, if today is the 3rd and they want to be billed on the first, then get the 1st day of next month... etc.

if params[:billing_day] == 1 && start_date.day > 1
  expire_date = start_date.at_beginning_of_month.next_month
elsif params[:billing_day] == 15 && start_date.day < 15
  expire_date = start_date.change(:day => 15)
elsif params[:billing_day] == 15 && start_date.day > 15
  expire_date = start_date.at_beginning_of_month.next_month.change(:day => 15)
else
  expire_date = start_date.change(:day => params[:billing_day])
end

It just seems crazy, surely it can be simplified in Rails. Thanks!

Answer 1

I would write something along the lines of

expire_date = start_date.change(:day => params[:billing_day])
if expire_date <= start_date
  expire_date += 1.month
end

You'd need to validate that a valid billing day was picked before this

Answer 2

Came up with this. But not sure if it's good idea

expire_date = if params[:billing_day] == 1 && start_date.day > 1
  start_date.at_beginning_of_month.next_month
elsif params[:billing_day] == 15 && start_date.day < 15
  start_date.change(:day => 15)
elsif params[:billing_day] == 15 && start_date.day > 15
  start_date.at_beginning_of_month.next_month.change(:day => 15)
else
  start_date.change(:day => params[:billing_day])
end

And what if params[:billing_day] == 15 && start_date.day == 15 ? What should happen?

Came up with this also, but it behaves a little different in the case of start_date.day == 15

expire_date = if params[:billing_day] == 1 && start_date.day > 1
  start_date.at_beginning_of_month.next_month
elsif params[:billing_day] == 15
    if start_date.day < 15
        start_date.change(:day => 15)
    else
        start_date.at_beginning_of_month.next_month.change(:day => 15)
    end
else
   start_date.change(:day => params[:billing_day])
end

Also notice that in Rails it's good practice to put logic in models, and since you are using params[] you are doing it in the controller.

Answer 3

class ExpireDate

  def initialize(billing_day, start_date)
    @billing_day = billing_day
    @start_date = start_date
  end 

  def expires_on
    if billing_day == 1
      return billing_on_1st
    elsif billing_day == 15
      return billing_on_15th
    else
      raise "Unknown billing_day"
    end
  end

  def billing_on_1st
    if @start_date.day > 1
      return @start_date.at_beginning_of_month.next_month
    else
      return @start_date.change(:day => @billing_day)
    end
  end

  def billing_on_15th
    if @start_date.day < 15
      return @start_date.change(:day => 15)
    else
      return @start_date.at_beginning_of_month.next_month.change(:day => 15)
    end
  end
end


expire_date = ExpireDate.new(params[:billing_day], start_date).expires_on