Ruby on rails 在rails计费系统中对发票应用付款

我已经为我的业务（无线ISP）编写了一个定制计费系统的大部分功能部件，但有一点让我为难

以下是基本概述： 这是一个为我的客户提供的定期计费系统，每月自动生成发票并发送给每个客户。然而，我需要允许支票/现金付款，因为我与当地客户打交道，而且还需要允许预付款，这样我就不能只使用Stripe的定期账单。基本上，付款与发票不直接关联，以允许此类付款

型号/发票.rb

class Invoice < ActiveRecord::Base
  belongs_to :customer
  has_many :line_items
  has_many :invoice_payments
  has_many :payments, through: :invoice_payments

class Payment < ActiveRecord::Base
  belongs_to :customer

class Customer < ActiveRecord::Base
  has_many :subscriptions, dependent: :destroy
  has_many :services, through: :subscriptions
  has_many :invoices, :order => 'id DESC'
  has_many :payments

def apply_unapplied_payments
  unpaid_invoices = invoices.find_by_status("unpaid")
  unapplied_payments = payments.where("invoice_id is null")
  unpaid_invoices.each do |invoice|
    # find the oldest unapplied payment
    # apply payment to this invoice
    # if payment > invoice, keep whatever amount is left and move to next invoice
    # apply leftover amount to invoice, if invoice is still unpaid, move to next unapplied payment
  end
  customer.update_balance
end

关于如何填写伪代码有什么建议吗？我对任何级别的重构都持开放态度，所以如果你能想出更好的方法来处理这个问题，请告诉我

下面是我要做的（可能需要付款和发票类中的一些助手方法）：

---

明亮的我没有那样想，而是陷入了思考。每一个循环。

def apply_unapplied_payments
  unpaid_invoices = invoices.find_by_status("unpaid")
  unapplied_payments = payments.where("invoice_id is null")
  invoice = unpaid_invoices.shift
  payment = unapplied_payments.shift
  while invoice && invoice.remaining_balance > 0 && payment && payment.remaining_credit > 0
      apply_payment_to_invoice(invoice, payment)
      invoice = unpaid_invoices.shift    if invoice.remaining_balance == 0
      payment = unapplied_payments.shift if payment.remaining_credit  == 0
  end
end