F8: Pricing, Promotions & Stacking Rules

Technical Overview

The Pricing Engine (pricing/pricing.py, pricing/promotions.py) computes dynamic flash-sale prices while strictly enforcing business guardrails:

1. Original Price Preservation: Baseline catalog price is always preserved.
2. Price Floor Validation: Effective price can never drop below a hard floor (e.g. wholesale cost).
3. Maximum Discount Cap: Total promotional discount is capped at a strict maximum percentage (e.g. 90%).
4. Promotion Stacking Rules: Prevents unapproved coupon and promotional stacking under concurrency.

Trace & Implementation

• Source Files: backend/src/pricing/pricing.py:11-100, backend/src/pricing/promotions.py:34-110
• Key Classes: PricingEngine, CouponManager
• Key Functions: resolve_price(), apply_fixed_discount(), validate_price_floor()

Architecture & Promotion Evaluation Flow

Say It Out Loud

"I built the pricing and promotion engine in src/pricing/pricing.py to ensure that flash-sale discounts never lead to negative margins or revenue leaks.

When a campaign is active, our pricing engine calculates the promotional price in integer cents, avoiding floating-point rounding errors.

It enforces three strict safety checks: first, the final sale price is validated against a minimum price floor so products are never sold below cost; second, maximum discount caps prevent runaway promotional compounding; and third, atomic coupon redemption ensures coupons cannot be double-used under concurrent requests."