from __future__ import print_function
from random import randint

def n_low_bits(n, value, bits=8):
    " returns n low bits of ord of c shifted as upper n bits) "
    return (value & ( (2 ** bits - 1) >> (bits - n) )) << (bits - n)

assert n_low_bits(5, ord('T')) == 0b10100000

def zbin(c, bits=8):
    try:
        return bin(ord(c))[2:].zfill(bits)
    except TypeError:
        return bin(c)[2:].zfill(bits)

                     
# shift bits n bits left and fil ends with random bits
def scramble(message, n, bits=8):
    # noice bits for ends not to leave tell tale zero tails
    # positive bits modulo number of bits
    n = n % bits
    values = 2**bits
    
    # for more than byte wide ord works but not chr
    char = unichr if bits > 8 else chr
    start, end = randint(1,2**bits-1), randint(1,2**bits-1)
    # take out need by dealing last letter separately, by adding end to message
    message = message + char(end)
    scrambleed = ""
    bits_in = n_low_bits(n, start, bits)
    for character in message:
        bitshifted = bits_in | (ord(character) >> n)
        scrambleed += char(bitshifted)
        bits_in = n_low_bits(n, ord(character), bits) 
    return scrambleed

def unscramble(message, n, bits=8):
    values = 2**bits
    return scramble(message, -n, bits)[1:-1]

if __name__ == '__main__':
    #making more interesting looking output from unicode text: bits = 16,
    #however the shift is then revealed by the shift of eight zero bits of normal letters
    #for unicode input should first do a compression of the message (uncompression after unscramble)
    message, n, bits = 'Xor encryption sucks!', 4, 8
    print(message)
    print('Length %i' % len(message))
    print(n * ' ' + ''.join(zbin(c) for c in message))

    encoded = scramble(message, n, bits)
    print(''.join(zbin(c) for c in encoded))
    print(encoded)
    print('\nLength %i' % len(encoded))

    decoded = unscramble(encoded, n, bits)
    print('\nLength %i' % len(decoded))
    print(decoded)