#!/usr/bin/env python3
# Copyright (c) 2015-2021 The Bitcoin Core developers
# Distributed under the MIT software license, see the accompanying
# file COPYING or http://www.opensource.org/licenses/mit-license.php.

from argparse import ArgumentParser
from getpass import getpass
from secrets import token_hex, token_urlsafe
import hmac

def generate_salt(size):
    """Create size byte hex salt"""
    return token_hex(size)

def generate_password():
    """Create 32 byte b64 password"""
    return token_urlsafe(32)

def password_to_hmac(salt, password):
    m = hmac.new(salt.encode('utf-8'), password.encode('utf-8'), 'SHA256')
    return m.hexdigest()

def main():
    parser = ArgumentParser(description='Create login credentials for a JSON-RPC user')
    parser.add_argument('username', help='the username for authentication')
    parser.add_argument('password', help='leave empty to generate a random password or specify "-" to prompt for password', nargs='?')
    parser.add_argument('--output', dest='output', help='file to store credentials, to be used with -rpcauthfile')
    args = parser.parse_args()

    if not args.password:
        args.password = generate_password()
    elif args.password == '-':
        args.password = getpass()

    # Create 16 byte hex salt
    salt = generate_salt(16)
    password_hmac = password_to_hmac(salt, args.password)

    if args.output:
        file = open(args.output, "a", encoding="utf8")
        file.write(f"{args.username}:{salt}${password_hmac}\n")
        print(f'Your password:\n{args.password}')
    else:
        print('String to be appended to bitcoin.conf:')
        print(f'rpcauth={args.username}:{salt}${password_hmac}')
        print(f'Your password:\n{args.password}')

if __name__ == '__main__':
    main()
