from typing import Optional
from typing import List


def get_class_selector(config_name: str) -> Optional[List[str]]:
    """Determines the class selector, based on the config name. This enables support for configs,
    which train a model only on a subset of classes.

    :param config_name: Name of the config used for the training of the model.
    :return: List that can be used as class selector for a data set or None.
    """
    if "light" in config_name.lower():
        class_selector = ["light"]
    elif "dark" in config_name.lower():
        class_selector = ["dark"]
    else:
        class_selector = None
    return class_selector