如何使用开放/封闭原则或策略模式重构此ruby代码

# 原始代码
class PaymentProcessor
  def initialize(payment_method)
    @payment_method = payment_method
  end

  def process_payment(amount)
    if @payment_method == "credit_card"
      process_credit_card(amount)
    elsif @payment_method == "paypal"
      process_paypal(amount)
    elsif @payment_method == "bank_transfer"
      process_bank_transfer(amount)
    else
      raise "Invalid payment method"
    end
  end

  private

  def process_credit_card(amount)
    # 处理信用卡支付逻辑
  end

  def process_paypal(amount)
    # 处理PayPal支付逻辑
  end

  def process_bank_transfer(amount)
    # 处理银行转账支付逻辑
  end
end

# 重构后的代码
class PaymentProcessor
  def initialize(payment_method)
    @payment_method = payment_method
  end

  def process_payment(amount)
    payment_strategy.process_payment(amount)
  end

  private

  def payment_strategy
    case @payment_method
    when "credit_card"
      CreditCardPaymentStrategy.new
    when "paypal"
      PaypalPaymentStrategy.new
    when "bank_transfer"
      BankTransferPaymentStrategy.new
    else
      raise "Invalid payment method"
    end
  end
end

class PaymentStrategy
  def process_payment(amount)
    raise NotImplementedError, "Subclasses must implement this method"
  end
end

class CreditCardPaymentStrategy < PaymentStrategy
  def process_payment(amount)
    # 处理信用卡支付逻辑
  end
end

class PaypalPaymentStrategy < PaymentStrategy
  def process_payment(amount)
    # 处理PayPal支付逻辑
  end
end

class BankTransferPaymentStrategy < PaymentStrategy
  def process_payment(amount)
    # 处理银行转账支付逻辑
  end
end