import random
import subprocess
import string

POW_BITS = 25

def random_string(n):
    return ''.join(random.choice(string.ascii_lowercase) for _ in range(n))

def check_pow():
    r = random_string(10)

    # The user is asked to run this command in their terminal
    print(f"hashcash -mb{POW_BITS} {r}") # $ hashcash -mb25 <random_string>

    # hashcash calculates the opposing hash, and the user copy pastes it into solution
    solution = input("Solution:").strip()

    # Check that the solution is correct
    if subprocess.call(["hashcash", f"-cdb{POW_BITS}", "-r", r, solution],
                       cwd="/tmp",
                       stdout=subprocess.DEVNULL,
                       stderr=subprocess.DEVNULL) != 0:
        raise Exception("Invalid PoW")