#task1
from struct import pack
import sys


def calc_check_sum(s, polyn):
    s += '0' * (len(polyn) - 1)
    i = 0
    res = ""
    while True:
        if res == "0":
            while i < len(s) and s[i] == '0':
                i += 1
            if i == len(s):
                return res
            res = s[i]
            i += 1

        while i < len(s) and len(res) < len(polyn):
            res += s[i]
            i += 1
        if len(res) < len(polyn):
            return res

        res = '{0:b}'.format(int(res, 2) ^ int(polyn, 2))


def error():
    print("The arguments are expected...\n--check [file]    to check is the checksum correct according to the CRC-8\n--build [file]    to calculate checksum and add it to the end of the file")


def append_bytes(file, addition):
    for c in addition:
        file.write(pack('1B', int(c)))


def main():
    if len(sys.argv) != 3 or sys.argv[1] not in ['--check', '--build']:
        error()
        return
    file = open(sys.argv[2], 'r+b')
    s = ""

    while True:
        cur_byte = file.read(1)
        if not cur_byte:
            break
        s += '{0:b}'.format(ord(cur_byte))
    print("Bytes = ", s, sep="")

    polyn = input("Enter the polynom for the CRC\n")
    check_sum = calc_check_sum(s, polyn)

    if sys.argv[1] == '--build':
        addition = '0' * (len(polyn) - len(check_sum) - 1) + check_sum
        print("Addition = ", addition, sep="")

        append_bytes(file, addition)
        file.close()

        print("The Check Sum is succesfully added to the end of the file.")
    else:
        if check_sum == '0':
            print("The file is correct.")
        else:
            print("The file is damaged.\nDelta = ", check_sum)


if __name__ == "__main__":
main()




#task5
import sys

def encode(key, cycle):
    for line in sys.stdin:
        for c in line:
            idx = cycle.index(ord(c))
            print(chr(cycle[(idx + key) % len(cycle)]), end="")
        print()


if __name__ == "__main__":
    cycle = list(range(48, 58)) + list(range(1040, 1104)) + \
        list(range(32, 47)) + list(range(58, 64))

    key = int(input("Enter encoding key\n"))
    cipher_type = input("Enter coding type (encode/decode)\n")
    print("Enter message")

    for line in sys.stdin:
        for c in line:
            if (ord(c) == 10):
                continue;
            idx = cycle.index(ord(c))

            if (cipher_type[0] == 'e'):
                idx = (idx + key) % len(cycle)
            else:
                idx = (idx - key + len(cycle)) % len(cycle)

            print(chr(cycle[idx]), end="")
print()