The ClinicFlow Domain Model: Entities and Value Objects

// Appointment.cs — internal factory method
internal static Appointment Schedule(
    Guid patientId,
    Guid doctorId,
    Guid appointmentTypeId,
    DateOnly scheduledDate,
    TimeRange timeRange,
    string? patientNotes = null
)
{
    if (patientId == Guid.Empty)
        throw new DomainValidationException(DomainErrors.Validation.ValueRequired);
    if (doctorId == Guid.Empty)
        throw new DomainValidationException(DomainErrors.Validation.ValueRequired);
    if (appointmentTypeId == Guid.Empty)
        throw new DomainValidationException(DomainErrors.Validation.ValueRequired);
    if (timeRange is null)
        throw new DomainValidationException(DomainErrors.General.RequiredFieldNull);

    var appointment = new Appointment(
        patientId, doctorId, appointmentTypeId, scheduledDate, timeRange, patientNotes
    );

    appointment.AddDomainEvent(new AppointmentScheduledEvent(appointment));

    return appointment;
}

// Scheduled → CheckedIn
public void CheckIn(DateOnly checkedInAt, string? receptionistNotes = null)
{
    if (Status is not AppointmentStatus.Scheduled)
        throw new DomainValidationException(DomainErrors.Appointment.CannotCheckIn);
    Status = AppointmentStatus.CheckedIn;
    // ...
}

// CheckedIn → InProgress  (only by the owning doctor)
public void Start(Guid initiatorDoctorId, DateTime startedAt)
{
    if (initiatorDoctorId != DoctorId)
        throw new DomainValidationException(DomainErrors.Appointment.UnauthorizedDoctor);
    if (Status is not AppointmentStatus.CheckedIn)
        throw new DomainValidationException(DomainErrors.Appointment.CannotStart);
    Status = AppointmentStatus.InProgress;
    // ...
}

// InProgress → Completed
public void Complete(DateTime completedAt)
{
    if (Status is not AppointmentStatus.InProgress)
        throw new DomainValidationException(DomainErrors.Appointment.CannotComplete);
    Status = AppointmentStatus.Completed;
    // ...
}

// Scheduled → RequiresReassignment (when the doctor is suspended)
internal void MarkAsRequiresReassignment()
{
    if (Status is not AppointmentStatus.Scheduled)
        throw new DomainValidationException(DomainErrors.Appointment.CannotReassign);
    Status = AppointmentStatus.RequiresReassignment;
}