Tell subscribers before a price rise

How to do it

A price rise changes the contract the customer agreed to. California's automatic renewal law requires clear notice of a material change before it applies, and EU contract terms usually need advance notice too. Create the new price in the versioned catalogue. Store one notice row per subscription with the time it was sent. Move a subscription to the new price only when its notice is at least 30 days old. Anyone who cancels before that date keeps the old price until the end.

Example

const NOTICE_DAYS = 30
const DAY_MS = 24 * 60 * 60 * 1000

function mayMoveToNewPrice(notice, now = new Date()) {
  return Boolean(notice) && now.getTime() - notice.sentAt.getTime() >= NOTICE_DAYS * DAY_MS
}

from datetime import datetime, timedelta, timezone

NOTICE = timedelta(days=30)

def may_move_to_new_price(notice, now: datetime | None = None) -> bool:
    now = now or datetime.now(timezone.utc)
    return notice is not None and now - notice.sent_at >= NOTICE

How to check

A test runs the price move with one subscriber notified 31 days ago and one notified 5 days ago. Only the first moves. The job refuses any subscription without a notice row.