hamming

#!/usr/bin/env python

from typing import Tuple

"""
Script to solve problems on 11-bit Hamming Code used in
Networks and Internet Systems.

### Usage: `$ ./hamming`
"""


def main() -> None:
    op = int(input("1. 11-bit Hamming Encoder\n" +
                   "2. Detect and Correct Error\n" +
                   "Choose option 1 or 2:\t"))
    if op == 1:
        seq = input('\nEnter 7-bit sequence:\t')
        print(f"Hamming code (11-bit):\t{getCode(seq)}")
    elif op == 2:
        seq = input('\nInput 11-bit sequence:\t')
        exists, error_bit, correct_seq = checkError(seq)
        data = dataSent(correct_seq)

        print(f"Error exists:\t\t{exists}\n" +
              f"Error bit:\t\t{error_bit}\n" +
              f"Correct Sequence:\t{correct_seq}\nData Sent:\t\t{data}")
    else:
        print('Please try again!')


def getCode(seq: str) -> str:
    bits = [int(bit) for bit in seq]
    for i in [3, 7, 9, 10]:
        bits.insert(i, 0)

    bits[10] = parity(bits, 0, 2, 4, 6, 8)  # r1
    bits[9] = parity(bits, 0, 1, 4, 5, 8)   # r2
    bits[7] = parity(bits, 4, 5, 6)         # r4
    bits[3] = parity(bits, 0, 1, 2)         # r8

    return ''.join([str(b) for b in bits])


def parity(bits: list, *indices: int) -> int:
    return sum([bits[i] for i in indices]) % 2


def checkError(seq: str) -> Tuple[bool, int, str]:
    bits = [int(bit) for bit in seq]
    p1 = parity(bits, 0, 2, 4, 6, 8, 10)
    p2 = parity(bits, 0, 1, 4, 5, 8, 9)
    p4 = parity(bits, 4, 5, 6, 7)
    p8 = parity(bits, 0, 1, 2, 3)

    new_parity = ''.join([str(i) for i in [p8, p4, p2, p1]])
    error_bit = int(new_parity, 2)
    exists = error_bit != 0

    if exists:
        idx = 11 - error_bit
        bits[idx] = int(not bits[idx])
    correct_seq = ''.join([str(b) for b in bits])

    return (exists, error_bit, correct_seq)


def dataSent(correct_seq: str) -> str:
    bits = list(correct_seq)
    return ''.join([b for i, b in enumerate(bits) if i not in [3, 7, 9, 10]])


if __name__ == '__main__':
    main()