Simple git credential helper in Python

git-credential-pass

#!/usr/bin/env python3
"""Simple script is a git credential helper which extracts password from
password store (pass).
"""

from argparse import ArgumentParser, Namespace
from dataclasses import dataclass
from subprocess import check_output
from sys import stdin, stdout
from typing import Optional, TextIO

parser = ArgumentParser(description=__doc__)
parser.add_argument('-t',
                    '--template',
                    type=str,
                    default='{username}@{host}',
                    help='password name template')
parser.add_argument('action', type=str, help='operation to execute')


@dataclass
class Credential:

    username: Optional[str] = None
    password: Optional[str] = None
    protocol: Optional[str] = None
    host: Optional[str] = None
    path: Optional[str] = None

    @staticmethod
    def read(fin: Optional[TextIO] = None) -> 'Credential':
        res = Credential()
        if not fin:
            fin = stdin
        for line in (line.strip() for line in stdin):
            if line == '':
                break

            if '=' not in line:
                raise RuntimeError('Unable to read credential from stdin.')

            param, value = line.split('=', 1)

            if param == 'username':
                res.username = value
            elif param == 'password':
                res.password = value
            elif param == 'protocol':
                res.protocol = value
            elif param == 'host':
                res.host = value
            elif param == 'path':
                res.path = value
        return res

    def write(self, fout: Optional[TextIO] = None):
        if not fout:
            fout = stdout

        def write_param(param: str):
            if (value := getattr(self, param, None)):
                fout.write(f'{param}={value}\n')

        write_param('username')
        write_param('password')
        write_param('protocol')
        write_param('host')
        write_param('port')


def get_credential(template: str):
    credential = Credential.read()
    pass_target = template.format(host=credential.host,
                                  username=credential.username)
    pass_output = check_output(['pass', pass_target])
    credential.password = pass_output.decode('utf-8').strip()
    credential.write()


def main(args: Namespace):
    if args.action == 'get':
        get_credential(args.template)


if __name__ == '__main__':
    main(parser.parse_args())