public class FixedWindowRecord extends AbstractTokenRecord {

    private Instant windowEnd;

    ...

    @Override
    public RateLimitRecord updateWith(RefillPolicy policy, Instant requestTs) {
        if (requestTs.isAfter(windowEnd)) {
            return new FixedWindowRecord(policy.getCapacity(), windowEnd.plus(policy.getSamplingPeriod()));
        }
        return this;
    }

    ...
}