import math
import hashlib

from package import package

class package_spliter:
    def __init__(self, target: package, mtu: int = 256) -> None:
        self.__target = target
        self.__mtu = mtu

    @property
    def mtu(self) -> int:
        return self.__mtu
    
    def __get_number_size(self) -> int:
        return 4

    def __get_header_size(self) -> int:
        return self.__get_number_size() * 3 + self.__get_crc_size()

    def __get_crc_size(self) -> int:
        return 20

    def __convert_number(self, number: int) -> bytes:
        return number.to_bytes(self.__get_number_size(), "big")

    def __calc_crc(self, part: bytes) -> bytes:
        return hashlib.sha1(part, usedforsecurity = False).digest()

    def __count_parts(self) -> int:
        single_package = self.mtu - self.__count_header_size()

        if single_package <= 0:
            raise RuntimeError("Package size is lower than zero.")

        return math.ceil(len(self.__content) / single_package)