package meta

const classField = "$id"

func ReadGeneric(r Reader, createFunc StructFactory, field string) (Readable, error) {
	if err := r.BeginContainer(field); err != nil {
		return nil, err
	}
	size, err := r.ContainerSize()
	if err != nil {
		return nil, err
	}
	if size == 0 {
		if err := r.EndContainer(); err != nil {
			return nil, err
		}

		return nil, nil
	}

	var classId uint32
	if err := r.ReadUint32(&classId, classField); err != nil {
		return nil, err
	}

	s, err := createFunc(classId)
	if err != nil {
		return nil, err
	}

	if err := s.ReadFields(r); err != nil {
		return nil, err
	}

	if err := r.EndContainer(); err != nil {
		return nil, err
	}

	return s, nil
}

func WriteGeneric(w Writer, s WritableClass, field string) error {
	if err := w.BeginContainer(s.FieldsCount()+1, field); err != nil {
		return err
	}
	if err := w.WriteUint32(s.ClassId(), classField); err != nil {
		return err
	}
	if err := s.WriteFields(w); err != nil {
		return err
	}
	return w.EndContainer()
}