Vacation.cs

public enum VacationRequestStatus
{
    Pending,
    Approved,
    Rejected
}

public class Employee
{
    public Guid Id { get; private set; }
    public bool IsManager { get; private set; }

    public Employee(Guid id, bool isManager)
    {
        Id = id;
        IsManager = isManager;
    }
}

public class VacationRequest
{
    public Guid EmployeeId { get; private set; }
    public VacationRequestStatus Status { get; private set; }

    public VacationRequest(Guid employeeId)
    {
        EmployeeId = employeeId;
        Status = VacationRequestStatus.Pending;
    }

    public void Approve(Employee approver)
    {
        if (approver.IsManager == false)
        {
            throw new UnauthorizedAccessException("Only managers can approve vacation requests.");
        }

        if (Status != VacationRequestStatus.Pending)
        {
            throw new InvalidOperationException("Only pending requests can be approved.");
        }

        Status = VacationRequestStatus.Approved;
    }
}