from mdrsclient.api.users import UsersApi
from mdrsclient.connection import MDRSConnection
from mdrsclient.exceptions import UnauthorizedException


def token_check(connection: MDRSConnection) -> None:
    """
    Bring the access token up to date before a request goes out.

    Refreshing is a read-modify-write over a cache shared with every other client
    process on this machine, and a rotating provider stops honouring the refresh token
    it replaces. Two processes reaching this at once would otherwise both send the same
    token, and the loser would be left holding one the server no longer accepts, so the
    whole sequence runs under a lock that spans processes and the cache is re-read
    inside it.
    """
    with connection.lock:
        token = connection.token
        if token is None or not (token.is_refresh_required or token.is_expired):
            # Nothing to do, which is the answer for almost every request. The lock below
            # reaches across processes and is held for a round trip, so it is worth
            # knowing that before taking it.
            return
        with connection.cache_lock():
            connection.reload_cache()
            token = connection.token
            if token is None:
                return
            if token.is_expired:
                connection.logout()
                return
            if not token.is_refresh_required:
                return
            user_api = UsersApi(connection)
            try:
                connection.token = user_api.tokenRefresh(token)
            except UnauthorizedException:
                connection.logout()