#!/bin/env python3

def text_to_bits(text, encoding='utf-8', errors='surrogatepass'):
    bits = bin(int.from_bytes(text.encode(encoding, errors), 'big'))[2:]
    return bits.zfill(8 * ((len(bits) + 7) // 8))

def bits_to_hex(bits):
    if len(bits) % 8:
        raise RuntimeError('Wrong number of bits')
    parts = [bits[i:i+8] for i in range(0, len(bits), 8)]
    return ','.join("0x{:02x}".format(int(section, 2)) for section in parts)

def triple(string):
    for character in string:
        yield character
        yield character
        yield character

if __name__ == "__main__":
    import argparse as ap
    import random as rnd

    class NoiseAction(ap.Action):
        def __call__(self, parser, namespace, values, option_string=None):
            if values < 0 or values > 1:
                parser.error("allowed noise values are from the interval [0, 1]")
            setattr(namespace, self.dest, values)

    parser = ap.ArgumentParser(description='Script for generating inputs for the isu8-cv5-1 practice')
    parser.add_argument('input', type=str, help='string to be encoded')
    parser.add_argument('-n', '--noise', dest='noise', action=NoiseAction, type=float, default=0.5, help='channel noise level (0 = no noise, 1 = maximum noise, 0.5 by default)')
    parser.add_argument('-u', '--unsafe', dest='unsafe', action='store_true', help='allow for a message corruption (noise value of 1 implies a random output with this option)')

    # parse input arguments
    args = parser.parse_args()

    # get a bit representation of the input
    bits = text_to_bits(args.input)

    # triple each bit, convert to list
    bitlist = list(triple(bits))
    #print(''.join(bitlist))

    # flip some bits
    args.noise = args.noise / 2
    if args.noise > 0:
        if args.unsafe:
            # determine a random flip for each of the bit
            for i in range(len(bitlist)):
                if rnd.random() > args.noise:
                    continue
                if bitlist[i] == '0':
                    bitlist[i] = '1'
                else:
                    bitlist[i] = '0'
        else:
            # determine a random flip for a single bit in each group
            for i in range(0, len(bitlist), 3):
                if rnd.random() > args.noise:
                    continue
                i += rnd.randrange(3)
                if bitlist[i] == '0':
                    bitlist[i] = '1'
                else:
                    bitlist[i] = '0'

    # encode the bits to hex
    #print(''.join(bitlist))
    print(bits_to_hex(''.join(bitlist)))