Constraint atMostThreeConsecutiveShifts(ConstraintFactory constraintFactory) {
    return constraintFactory.from(Employee.class)
                     .join(Shift.class, Joiners.equal(Function.identity(), Shift::getEmployee)
                     .collect((employee, shift) -> employee, consecutiveIntervals((employee,shift) -> shift, Shift::getStartDateTime, Shift::getEndDateTime))
                     .flattenLast(IntervalCluster::getSequences)
                     .filter((employee,sequence) -> sequence.size() > 3)
                     .penalize("At most 3 consecutive shifts", HardSoftScore.ONE_HARD);
}