import os
import sys
from Crypto.Cipher import AES
from Crypto.Hash import SHA256


def main(args=None):
    if len(args) < 2:
        print("Usage: python aes_decipher.py <file> <key>")
        return

    fname = args[0]
    if not os.path.exists(fname) or os.path.isdir(fname) or not os.path.isfile(fname):
        print("File does not exist or is not a file")
        return

    key_arg: str = args[1]
    if len(key_arg) < 16:
        h = SHA256.new()
        h.update(key_arg.encode('utf-8'))
        key = h.digest()[0:16]
        cipher = AES.new(key, AES.MODE_ECB)
    else:
        key = key_arg[0:16]
        cipher = AES.new(bytes(key.encode('utf-u')), AES.MODE_ECB)

    fsize = os.path.getsize(fname)

    with open(fname, 'rb') as file:
        run = True
        while run:
            block = file.read(AES.block_size)
            text = cipher.decrypt(block)

            if file.tell() == fsize:
                has_padding = True
                i = AES.block_size - text[-1]
                while has_padding and i < len(text):
                    has_padding = text[i] == text[-1]
                    i += 1

                if has_padding:
                    text = text[:AES.block_size - text[-1]]

                run = False

            os.write(1, text)


if __name__ == '__main__':
    main(sys.argv[1:])