#!/usr/bin/env python3

import itertools
import requests
import string

URL = "https://projecteuler.net/project/resources/p059_cipher.txt"

def get_ciphertext(url):
    resp = requests.get(url)
    return resp.text


def generate_keys(letters, length):
    perms = itertools.permutations(letters, length)
    yield from perms


def ints_to_string(numbers):
    return [chr(num) for num in numbers]


def string_to_ints(letters):
    return [ord(letter) for letter in letters]


def xor_lists(xs, ys):
    if len(xs) != len(ys):
        raise Exception("Lists must be the same length")

    return [a ^ b for a, b in zip(xs, ys)]


def main():
    text = get_ciphertext(URL)
    cipher = [int(num) for num in text.split(',')]
    letters = string.ascii_lowercase
    common_words = ["the", "of", "to", "and", "in", "is", "it", "that"]
    for perm in generate_keys(letters, 3):
        key = "".join(list(perm))
        cycled = string_to_ints(list(key * (len(cipher) // len(key))))
        decrypt = "".join(ints_to_string(xor_lists(cipher, cycled)))
        if all(word in decrypt for word in common_words):
            print("Decrypted passage:")
            print(decrypt)
            print("Key: {0}".format(key))
            print("Sum: {0}".format(sum(xor_lists(cipher, cycled))))


if __name__ == "__main__":
    main()