#!/usr/bin/env python3

import random
import secrets
import os
import sys
import hashlib

DEFAULT_SECRET_PATH = '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 generate_secret(secret_path):
    print('Generating a new secret... ', end='')
    secret = create_secret()
    with open(secret_path, 'w') as f:
        f.write(secret)
    print('done. Send this to the other party:')
    print(secret)

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

    args = parser.parse_args()

    secret_path = args.secret if args.secret else DEFAULT_SECRET_PATH

    secret = ''
    if args.new_secret:
        if os.path.isfile(secret_path):
            choice = ''
            while choice.lower() != 'y' and choice.lower() != 'n':
                choice = input(f'Secret {secret_path} exists! Overwrite? [y/n]: ')
            if choice.lower() == 'y':
                generate_secret(secret_path)
        else:
            generate_secret(secret_path)

    try:
        secret = open(secret_path, 'r').read().strip()
    except FileNotFoundError:
        print(f'ERROR: Secret file {secret_path} could not be found.')
        sys.exit(1)
    print(f'Secret {secret_path} loaded.')

    random.seed(generate_seed(secret))

    print('The password of the month is:')
    print(generate_password())

if __name__ == '__main__':
    main()