Function getWeekStart

packages/billing/src/subscription.ts:124–132

(
  billingPeriodStart: Date,
  now: Date = new Date(),
)

 * Weeks start on the same day-of-week as the billing period started.
 */
export function getWeekStart(
  billingPeriodStart: Date,
  now: Date = new Date(),
): Date {
  const billingDayOfWeek = billingPeriodStart.getUTCDay()
  const currentDayOfWeek = now.getUTCDay()
  const daysBack = (currentDayOfWeek - billingDayOfWeek + 7) % 7
  return startOfDay(addDays(now, -daysBack))
}

/**
 * Get the end of the current billing-aligned week (start of next week).