18-Flash-Sale-Inventory

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F9: Timezone-Aware Scheduled Activation ​

Technical Overview ​

The Scheduled Activation Engine (sales/activation.py) manages the lifecycle transition of flash-sale campaigns from SCHEDULED to ACTIVE. It guarantees:

  1. Documented Tolerance: Activation occurs within $\le 1.0$ second of the target timestamp.
  2. Timezone & DST Robustness: Converts IANA wall-clock times to UTC and correctly handles Daylight Saving Time boundary transitions.

Trace & Implementation ​

  • Source Files: backend/src/sales/activation.py:22-120
  • Key Classes: TimezoneConversionService, ScheduledActivationEngine
  • Key Constant: ACTIVATION_TOLERANCE_SECONDS = 1.0

Scheduled Activation Sequence Diagram ​

Say It Out Loud ​

"I built the scheduled activation engine in src/sales/activation.py to ensure flash sales launch at the exact millisecond planned, regardless of timezone or Daylight Saving Time shifts.

All campaign start and end times are stored internally in UTC. The service uses Python's zoneinfo to convert localized wall-clock inputs into UTC, explicitly verifying whether intervals cross DST shift boundaries.

A background evaluation worker queries scheduled campaigns and activates those due within a tight 1.0-second tolerance window, updating campaign status to ACTIVE so product listings instantly reflect flash-sale pricing."