#!/usr/bin/env python3

import random
import secrets
import os
import hashlib

SECRET_FILE = 'secret'

def create_secret():
    return secrets.token_hex(128)

def generate_password():
    import string
    alphabet = string.ascii_letters + string.digits + '!"#$%&\'()*+,-./:;<=>?@[\\]^_`{|}'
    return ''.join(random.choice(alphabet) for i in range(24))

def month_timestamp():
    import datetime
    today = datetime.datetime.now()
    start_of_month = datetime.datetime(today.year, today.month, 1, 0, 0, 0, 0)
    return int(start_of_month.timestamp())

def generate_seed(secret):
    m = hashlib.sha256()
    m.update(bytes.fromhex(secret))
    m.update(str(month_timestamp()).encode())
    return m.digest()

def main():
    import argparse
    parser = argparse.ArgumentParser(prog='Remote Admin Password Solution', description='Generate rotating passwords based on a shared secret')
    parser.add_argument('--new-secret', action='store_true', help='generate a new secret')

    args = parser.parse_args()

    secret = ''
    if not os.path.isfile(SECRET_FILE) or args.new_secret:
        print('Generating a new secret... ', end='')
        secret = create_secret()
        with open(SECRET_FILE, 'w') as f:
            f.write(secret)
        print('done. Send this to the other party:')
        print(secret)

    else:
        secret = open(SECRET_FILE, 'r').read().strip()
        print('Secret loaded.')

    random.seed(generate_seed(secret))
    
    print('The password of the month is:')
    print(generate_password())

if __name__ == '__main__':
    main()