Summary

• This feature adds support for fetching customer coupons from Stripe and showing applied
  discounts in the product view (DueToday component).

Related Issues

• https://lindie.app/share/670cc31c69f9ab7d3d1d61e0fb2cc7c3b3ada74b/ENG-570

Type of Change

• Bug fix
• New feature
• Breaking change
• Refactor
• Other (please describe):

Checklist

• I have read the CONTRIBUTING.md
• My code follows the code style of this project
• I have added tests where applicable
• I have tested my changes locally
• I have linked relevant issues
• I have added screenshots for UI changes (if applicable)

Screenshots (if applicable)

Additional Context

■ File Changes
Backend

• cusRouter.ts
• Added /:customer_id/coupon route.
• handleGetCustomerCoupon.ts
• Extracted handler logic for retrieving coupon.
  Frontend
• CusService.ts
• Added getCustomerCoupon method.
• DueToday.tsx
• Added useEffect to fetch coupon on load.
• Added state to store coupon/discount.
• Extended rendering to include discount block and updated final total.

■ Additional Notes

• The discount block only appears when a valid coupon is applied on the customer in Stripe.
• Currently supports:
• Percentage discounts (percent_off).
• Fixed amount discounts (amount_off).
• Handles both recurring discounts (e.g. duration_in_months) and one-time coupons.
• Can be extended later to display coupon metadata (e.g. internal reward program ID).

■ Next Steps

• Add unit tests for the new API endpoint.
• Add UI tests to confirm discount calculations.
• (Optional) Show coupon metadata (e.g. reward program name) in the UI.