from utils import CipherUtils

CLEAR_LIST = [0, 1, 0, 1, 0, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 1, 1, 0, 0, 1]
INIT_STATE = [0, 1, 1, 0]
COEFFICIENTS = [1, 1, 1, 0]


def create_shift_register(init_state: [int], coefficients: [int]) -> [int]:
    """
    Creates and returns the maximum bit stream for the given input state via a linear shift register.
    Especially the coefficients are important as choosing the correct ones for any given shift register length
    will provide the maximum amount of bits before they repeat
    :param init_state: The initial bits in the shift register
    :param coefficients: The coefficients of every field in the shift register
    :return: The maximum length bit stream generated by the linear shift register
    """
    return_list = []
    current_state = init_state.copy()

    if (size := len(init_state)) != len(coefficients):
        print('Length of lists does not match.')
        exit()

    for x in range(2 ** size):
        return_list.append(current_state[-1])
        new_state_value = 0
        for i in range(size):
            new_state_value = (new_state_value + current_state[i] * coefficients[i]) % 2

        current_state.insert(0, new_state_value)
        current_state.pop(-1)

        if current_state == init_state:
            # For ideal coefficients, the output is perfectly fine.
            # However, for unideal coefficients, it might appear that we reach a state after lets say 1 iteration.
            # We still need to output [size] amount of bits, hence the following line.
            if x != (2 ** size) - 2:
                return_list.extend(current_state[1:][::-1])
            break

    return return_list


if __name__ == '__main__':
    key = create_shift_register(INIT_STATE, COEFFICIENTS)

    encrypted = CipherUtils.xor_two_lists(CLEAR_LIST, key)
    decrypted = CipherUtils.xor_two_lists(encrypted, key)
    print(CLEAR_LIST)
    print(encrypted)
    print(decrypted)