Implement a hybrid system that allows external services to apply discounts to carts through callbacks, while persisting those discounts for cart abandonment scenarios and performance optimization.

• Current discount system is tightly coupled to Commerce::Discount → Commerce::CartDiscount → Commerce::CartAdjustment chain
• External systems need to apply discounts that don't fit this rigid structure
• Discounts must persist for abandoned cart scenarios
• System should be performant and reliable even when external services are unavailable

Code is clean if it can be understood easily – by everyone on the team. Clean code can be read and enhanced by a developer other than its original author. With understandability comes readability, changeability, extensibility and maintainability.

1. Follow standard conventions.
2. Keep it simple stupid. Simpler is always better. Reduce complexity as much as possible.
3. Boy scout rule. Leave the campground cleaner than you found it.
4. Always find root cause. Always look for the root cause of a problem.

1. Open a browser

   # start an instance of firefox with selenium-webdriver
   driver = Selenium::WebDriver.for :firefox
   # :chrome -> chrome
   # :ie     -> iexplore