e-jambon/gist:4dc7817e3b3d12e022c59a9f78798188

• Design patterns are just tools that help us constructing a software.

** Template Method pattern In the Template Method pattern, we create a skeletal class and it is basis for various subclasses or concrete classes. Within in the skeletal class, there are abstract methods, which in turn, will be overridden by the methods of subclasses.

Let's take an example of simple payment system,

Usually, the payment process has the same flow regardless of the provider we use.

The flow of our example payment system is,

1. Authenticate the merchant (our application) with the provider
2. Send the User's card data with the amount of order
3. Receive confirmation or error from the provider

class StripePayment
  def initialize card, amount
    @api_key = ENV['STRIPE_API_KEY']
    @card = card
    @amount = amount
  end
  
  def process_payment!
    authenticate_merchant && make_payment
  end
  
  def authenticate_merchant
    begin
      return true if Stripe::Merchant.authenticate @api_key
    rescue Stripe::MerchantError => e
      Rails.logger.error "Cannot establish connection between Merchant and Provider."
      return false
    rescue Stripe::ProviderUnreachable => e
      Rails.logger.error "Provider unreachable."
      return false
    end
  end
  
  def make_payment
    begin
      return true if Stripe::Payment.process! @api_key, @card, @amount
    rescue Stripe::PaymentUnprocessable => e
      Rails.logger.error "Payment unprocessable, try again."
      return false
    end
  end
end