/**
 * One world seed per UTC-aligned period: floor(utcUnixSeconds / rotationSeconds).
 * Changing the slot triggers a full grid wipe on the server.
 */
export function computeWorldSeedState(rotationSeconds) {
  const rot = Math.max(60, Math.floor(rotationSeconds));
  const nowSec = Math.floor(Date.now() / 1000);
  const slot = Math.floor(nowSec / rot);
  const periodStart = slot * rot;
  const periodEnd = periodStart + rot;
  return {
    worldSeed: `swg-${slot}`,
    seedSlot: slot,
    seedPeriodEndsAtUtc: new Date(periodEnd * 1000).toISOString(),
    seedPeriodStartsAtUtc: new Date(periodStart * 1000).toISOString(),
  };
}