class package_part:
    def __init__(self, content: bytes) -> None:
        self.__content = content
        self.__current_count = None
        self.__packages_count = None

    def set_counter(self, current: int, packages_count: int) -> object:
        self.__current_count = current
        self.__packages_count = packages_count

        return self

    @staticmethod
    def get_header_size() -> None:
        return self.__number_size() * 3 + self.__crc_size()

    @classmethod
    def __number_to_bytes(cls, target: int) -> bytes:
        return target.to_bytes(cls.__number_size(), "big")

    @staticmethod
    def __number_size() -> int:
        return 5

    @staticmethod
    def __crc_size() -> int:
        return 20

    @staticmethod 
    def __calc_crt(target: bytes) -> bytes:
        return hashlib.sha1(target, usedforsecurity = False).digest()