from os import urandom
from itertools import count
from hashlib import sha256


class proofow:
    def __init__(self, difficulty):
        self._base = urandom(32)
        self._target = 2 ** (256 - difficulty)

    def work(self):
        for nonce in count():
            if self.verify(nonce):
                return nonce

    def verify(self, nonce):
        hexresult = sha256(self._base + str(nonce).encode()).hexdigest()
        return int(hexresult, 16) < self._target