#!/usr/bin/env python3
"""The multi-user notebook application"""

# Copyright (c) Jupyter Development Team.
# Distributed under the terms of the Modified BSD License.

import atexit
import binascii
from datetime import datetime
from getpass import getuser
import logging
from operator import itemgetter
import os
import re
import signal
import sys
from textwrap import dedent
from urllib.parse import urlparse

if sys.version_info[:2] < (3, 3):
    raise ValueError("Python < 3.3 not supported: %s" % sys.version)

from jinja2 import Environment, FileSystemLoader

from sqlalchemy.exc import OperationalError

from tornado.httpclient import AsyncHTTPClient
import tornado.httpserver
from tornado.ioloop import IOLoop, PeriodicCallback
from tornado.log import app_log, access_log, gen_log
import tornado.options
from tornado import gen, web
from tornado.platform.asyncio import AsyncIOMainLoop
AsyncIOMainLoop().install()

from traitlets import (
    Unicode, Integer, Dict, TraitError, List, Bool, Any,
    Type, Set, Instance, Bytes, Float,
    observe, default,
)
from traitlets.config import Application, catch_config_error

here = os.path.dirname(__file__)

import jupyterhub
from . import handlers, apihandlers
from .handlers.static import CacheControlStaticFilesHandler, LogoHandler
from .services.service import Service

from . import crypto
from . import dbutil, orm
from .user import User, UserDict
from .oauth.store import make_provider
from ._data import DATA_FILES_PATH
from .log import CoroutineLogFormatter, log_request
from .proxy import Proxy, ConfigurableHTTPProxy
from .traitlets import URLPrefix, Command
from .utils import (
    url_path_join,
    ISO8601_ms, ISO8601_s,
)
# classes for config
from .auth import Authenticator, PAMAuthenticator
from .crypto import CryptKeeper
from .spawner import Spawner, LocalProcessSpawner
from .objects import Hub, Server

# For faking stats
from .emptyclass import EmptyClass


common_aliases = {
    'log-level': 'Application.log_level',
    'f': 'JupyterHub.config_file',
    'config': 'JupyterHub.config_file',
    'db': 'JupyterHub.db_url',
}


aliases = {
    'base-url': 'JupyterHub.base_url',
    'y': 'JupyterHub.answer_yes',
    'ssl-key': 'JupyterHub.ssl_key',
    'ssl-cert': 'JupyterHub.ssl_cert',
    'ip': 'JupyterHub.ip',
    'port': 'JupyterHub.port',
    'pid-file': 'JupyterHub.pid_file',
    'log-file': 'JupyterHub.extra_log_file',
}
token_aliases = {}
token_aliases.update(common_aliases)
aliases.update(common_aliases)

flags = {
    'debug': ({'Application': {'log_level': logging.DEBUG}},
        "set log level to logging.DEBUG (maximize logging output)"),
    'generate-config': ({'JupyterHub': {'generate_config': True}},
        "generate default config file"),
    'no-db': ({'JupyterHub': {'db_url': 'sqlite:///:memory:'}},
        "disable persisting state database to disk"
    ),
    'upgrade-db': ({'JupyterHub': {'upgrade_db': True}},
        """Automatically upgrade the database if needed on startup.

        Only safe if the database has been backed up.
        Only SQLite database files will be backed up automatically.
        """
    ),
    'no-ssl': ({'JupyterHub': {'confirm_no_ssl': True}},
        "[DEPRECATED in 0.7: does nothing]"
    ),
}

COOKIE_SECRET_BYTES = 32  # the number of bytes to use when generating new cookie secrets

HEX_RE = re.compile('^([a-f0-9]{2})+$', re.IGNORECASE)

class NewToken(Application):
    """Generate and print a new API token"""
    name = 'jupyterhub-token'
    version = jupyterhub.__version__
    description = """Generate and return new API token for a user.

    Usage:

        jupyterhub token [username]
    """

    examples = """
        $> jupyterhub token kaylee
        ab01cd23ef45
    """

    name = Unicode(getuser())

    aliases = token_aliases
    classes = []

    def parse_command_line(self, argv=None):
        super().parse_command_line(argv=argv)
        if not self.extra_args:
            return
        if len(self.extra_args) > 1:
            print("Must specify exactly one username", file=sys.stderr)
            self.exit(1)
        self.name = self.extra_args[0]

    def start(self):
        hub = JupyterHub(parent=self)
        hub.load_config_file(hub.config_file)
        hub.init_db()
        hub.init_users()
        user = orm.User.find(hub.db, self.name)
        if user is None:
            print("No such user: %s" % self.name, file=sys.stderr)
            self.exit(1)
        token = user.new_api_token()
        print(token)


class UpgradeDB(Application):
    """Upgrade the JupyterHub database schema."""

    name = 'jupyterhub-upgrade-db'
    version = jupyterhub.__version__
    description = """Upgrade the JupyterHub database to the current schema.

    Usage:

        jupyterhub upgrade-db
    """
    aliases = common_aliases
    classes = []

    def start(self):
        hub = JupyterHub(parent=self)
        hub.load_config_file(hub.config_file)
        self.log = hub.log
        dbutil.upgrade_if_needed(hub.db_url, log=self.log)


class JupyterHub(Application):
    """An Application for starting a Multi-User Jupyter Notebook server."""
    name = 'jupyterhub'
    version = jupyterhub.__version__

    description = """Start a multi-user Jupyter Notebook server

    Spawns a configurable-http-proxy and multi-user Hub,
    which authenticates users and spawns single-user Notebook servers
    on behalf of users.
    """

    examples = """

    generate default config file:

        jupyterhub --generate-config -f /etc/jupyterhub/jupyterhub_config.py

    spawn the server on 10.0.1.2:443 with https:

        jupyterhub --ip 10.0.1.2 --port 443 --ssl-key my_ssl.key --ssl-cert my_ssl.cert
    """

    aliases = Dict(aliases)
    flags = Dict(flags)

    raise_config_file_errors = True

    subcommands = {
        'token': (NewToken, "Generate an API token for a user"),
        'upgrade-db': (UpgradeDB, "Upgrade your JupyterHub state database to the current version."),
    }

    classes = List([
        Spawner,
        LocalProcessSpawner,
        Authenticator,
        PAMAuthenticator,
        CryptKeeper,
    ])

    load_groups = Dict(List(Unicode()),
        help="""Dict of 'group': ['usernames'] to load at startup.

        This strictly *adds* groups and users to groups.

        Loading one set of groups, then starting JupyterHub again with a different
        set will not remove users or groups from previous launches.
        That must be done through the API.
        """
    ).tag(config=True)

    config_file = Unicode('jupyterhub_config.py',
        help="The config file to load",
    ).tag(config=True)
    generate_config = Bool(False,
        help="Generate default config file",
    ).tag(config=True)
    answer_yes = Bool(False,
        help="Answer yes to any questions (e.g. confirm overwrite)"
    ).tag(config=True)
    pid_file = Unicode('',
        help="""File to write PID
        Useful for daemonizing jupyterhub.
        """
    ).tag(config=True)
    cookie_max_age_days = Float(14,
        help="""Number of days for a login cookie to be valid.
        Default is two weeks.
        """
    ).tag(config=True)
    last_activity_interval = Integer(300,
        help="Interval (in seconds) at which to update last-activity timestamps."
    ).tag(config=True)
    proxy_check_interval = Integer(30,
        help="Interval (in seconds) at which to check if the proxy is running."
    ).tag(config=True)
    service_check_interval = Integer(60,
        help="Interval (in seconds) at which to check connectivity of services with web endpoints."
    ).tag(config=True)

    data_files_path = Unicode(DATA_FILES_PATH,
        help="The location of jupyterhub data files (e.g. /usr/local/share/jupyter/hub)"
    ).tag(config=True)

    template_paths = List(
        help="Paths to search for jinja templates.",
    ).tag(config=True)

    @default('template_paths')
    def _template_paths_default(self):
        return [os.path.join(self.data_files_path, 'templates')]

    confirm_no_ssl = Bool(False,
        help="""DEPRECATED: does nothing"""
    ).tag(config=True)
    ssl_key = Unicode('',
        help="""Path to SSL key file for the public facing interface of the proxy

        When setting this, you should also set ssl_cert
        """
    ).tag(config=True)
    ssl_cert = Unicode('',
        help="""Path to SSL certificate file for the public facing interface of the proxy

        When setting this, you should also set ssl_key
        """
    ).tag(config=True)
    ip = Unicode('',
        help="The public facing ip of the whole application (the proxy)"
    ).tag(config=True)

    subdomain_host = Unicode('',
        help="""Run single-user servers on subdomains of this host.

        This should be the full `https://hub.domain.tld[:port]`.

        Provides additional cross-site protections for javascript served by single-user servers.

        Requires `<username>.hub.domain.tld` to resolve to the same host as `hub.domain.tld`.

        In general, this is most easily achieved with wildcard DNS.

        When using SSL (i.e. always) this also requires a wildcard SSL certificate.
        """
    ).tag(config=True)

    def _subdomain_host_changed(self, name, old, new):
        if new and '://' not in new:
            # host should include '://'
            # if not specified, assume https: You have to be really explicit about HTTP!
            self.subdomain_host = 'https://' + new

    domain = Unicode(
        help="domain name, e.g. 'example.com' (excludes protocol, port)"
    )

    @default('domain')
    def _domain_default(self):
        if not self.subdomain_host:
            return ''
        return urlparse(self.subdomain_host).hostname

    port = Integer(8000,
        help="The public facing port of the proxy"
    ).tag(config=True)
    base_url = URLPrefix('/',
        help="The base URL of the entire application"
    ).tag(config=True)
    logo_file = Unicode('',
        help="Specify path to a logo image to override the Jupyter logo in the banner."
    ).tag(config=True)

    @default('logo_file')
    def _logo_file_default(self):
        return os.path.join(self.data_files_path, 'static', 'images', 'jupyter.png')

    jinja_environment_options = Dict(
        help="Supply extra arguments that will be passed to Jinja environment."
    ).tag(config=True)

    proxy_class = Type(ConfigurableHTTPProxy, Proxy,
                       help="""Select the Proxy API implementation."""
                       ).tag(config=True)

    proxy_cmd = Command([], config=True,
        help="DEPRECATED since version 0.8. Use ConfigurableHTTPProxy.command",
    ).tag(config=True)

    debug_proxy = Bool(False,
        help="DEPRECATED since version 0.8: Use ConfigurableHTTPProxy.debug",
    ).tag(config=True)
    proxy_auth_token = Unicode(
        help="DEPRECATED since version 0.8: Use ConfigurableHTTPProxy.auth_token"
    ).tag(config=True)

    _proxy_config_map = {
        'proxy_cmd': 'command',
        'debug_proxy': 'debug',
        'proxy_auth_token': 'auth_token',
    }
    @observe(*_proxy_config_map)
    def _deprecated_proxy_config(self, change):
        dest = self._proxy_config_map[change.name]
        self.log.warning("JupyterHub.%s is deprecated in JupyterHub 0.8, use ConfigurableHTTPProxy.%s", change.name, dest)
        self.config.ConfigurableHTTPProxy[dest] = change.new

    proxy_api_ip = Unicode(
        help="DEPRECATED since version 0.8 : Use ConfigurableHTTPProxy.api_url"
    ).tag(config=True)
    proxy_api_port = Integer(
        help="DEPRECATED since version 0.8 : Use ConfigurableHTTPProxy.api_url"
    ).tag(config=True)
    @observe('proxy_api_port', 'proxy_api_ip')
    def _deprecated_proxy_api(self, change):
        self.log.warning("JupyterHub.%s is deprecated in JupyterHub 0.8, use ConfigurableHTTPProxy.api_url", change.name)
        self.config.ConfigurableHTTPProxy.api_url = 'http://{}:{}'.format(
            self.proxy_api_ip or '127.0.0.1',
            self.proxy_api_port or self.port + 1,
        )

    hub_port = Integer(8081,
        help="The port for the Hub process"
    ).tag(config=True)
    hub_ip = Unicode('127.0.0.1',
        help="""The ip address for the Hub process to *bind* to.

        See `hub_connect_ip` for cases where the bind and connect address should differ.
        """
    ).tag(config=True)

    hub_connect_ip = Unicode('',
        help="""The ip or hostname for proxies and spawners to use
        for connecting to the Hub.

        Use when the bind address (`hub_ip`) is 0.0.0.0 or otherwise different
        from the connect address.

        Default: when `hub_ip` is 0.0.0.0, use `socket.gethostname()`, otherwise use `hub_ip`.

        .. versionadded:: 0.8
        """
    ).tag(config=True)

    hub_connect_port = Integer(
        0,
        help="""
        The port for proxies & spawners to connect to the hub on.

        Used alongside `hub_connect_ip`

        .. versionadded:: 0.8
        """
    ).tag(config=True)

    hub_prefix = URLPrefix('/hub/',
        help="The prefix for the hub server.  Always /base_url/hub/"
    )

    @default('hub_prefix')
    def _hub_prefix_default(self):
        return url_path_join(self.base_url, '/hub/')

    @observe('base_url')
    def _update_hub_prefix(self, change):
        """add base URL to hub prefix"""
        self.hub_prefix = self._hub_prefix_default()

    trust_user_provided_tokens = Bool(False,
        help="""Trust user-provided tokens (via JupyterHub.service_tokens)
        to have good entropy.

        If you are not inserting additional tokens via configuration file,
        this flag has no effect.

        In JupyterHub 0.8, internally generated tokens do not
        pass through additional hashing because the hashing is costly
        and does not increase the entropy of already-good UUIDs.

        User-provided tokens, on the other hand, are not trusted to have good entropy by default,
        and are passed through many rounds of hashing to stretch the entropy of the key
        (i.e. user-provided tokens are treated as passwords instead of random keys).
        These keys are more costly to check.

        If your inserted tokens are generated by a good-quality mechanism,
        e.g. `openssl rand -hex 32`, then you can set this flag to True
        to reduce the cost of checking authentication tokens.
        """
    ).tag(config=True)
    cookie_secret = Bytes(
        help="""The cookie secret to use to encrypt cookies.

        Loaded from the JPY_COOKIE_SECRET env variable by default.

        Should be exactly 256 bits (32 bytes).
        """
    ).tag(
        config=True,
        env='JPY_COOKIE_SECRET',
    )
    @observe('cookie_secret')
    def _cookie_secret_check(self, change):
        secret = change.new
        if len(secret) > COOKIE_SECRET_BYTES:
            self.log.warning("Cookie secret is %i bytes.  It should be %i.",
                len(secret), COOKIE_SECRET_BYTES,
            )

    cookie_secret_file = Unicode('jupyterhub_cookie_secret',
        help="""File in which to store the cookie secret."""
    ).tag(config=True)

    api_tokens = Dict(Unicode(),
        help="""PENDING DEPRECATION: consider using service_tokens

        Dict of token:username to be loaded into the database.

        Allows ahead-of-time generation of API tokens for use by externally managed services,
        which authenticate as JupyterHub users.

        Consider using service_tokens for general services that talk to the JupyterHub API.
        """
    ).tag(config=True)

    @observe('api_tokens')
    def _deprecate_api_tokens(self, change):
        self.log.warning("JupyterHub.api_tokens is pending deprecation"
            " since JupyterHub version 0.8."
            "  Consider using JupyterHub.service_tokens."
            "  If you have a use case for services that identify as users,"
            " let us know: https://github.com/jupyterhub/jupyterhub/issues"
        )

    service_tokens = Dict(Unicode(),
        help="""Dict of token:servicename to be loaded into the database.

        Allows ahead-of-time generation of API tokens for use by externally managed services.
        """
    ).tag(config=True)

    services = List(Dict(),
        help="""List of service specification dictionaries.

        A service

        For instance::

            services = [
                {
                    'name': 'cull_idle',
                    'command': ['/path/to/cull_idle_servers.py'],
                },
                {
                    'name': 'formgrader',
                    'url': 'http://127.0.0.1:1234',
                    'api_token': 'super-secret',
                    'environment':
                }
            ]
        """
    ).tag(config=True)
    _service_map = Dict()

    authenticator_class = Type(PAMAuthenticator, Authenticator,
        help="""Class for authenticating users.

        This should be a class with the following form:

        - constructor takes one kwarg: `config`, the IPython config object.

        - is a tornado.gen.coroutine
        - returns username on success, None on failure
        - takes two arguments: (handler, data),
          where `handler` is the calling web.RequestHandler,
          and `data` is the POST form data from the login page.
        """
    ).tag(config=True)

    authenticator = Instance(Authenticator)

    @default('authenticator')
    def _authenticator_default(self):
        return self.authenticator_class(parent=self, db=self.db)

    allow_named_servers = Bool(False,
        help="Allow named single-user servers per user"
    ).tag(config=True)

    # class for spawning single-user servers
    spawner_class = Type(LocalProcessSpawner, Spawner,
        help="""The class to use for spawning single-user servers.

        Should be a subclass of Spawner.
        """
    ).tag(config=True)

    concurrent_spawn_limit = Integer(
        100,
        help="""
        Maximum number of concurrent users that can be spawning at a time.

        Spawning lots of servers at the same time can cause performance
        problems for the Hub or the underlying spawning system.
        Set this limit to prevent bursts of logins from attempting
        to spawn too many servers at the same time.

        This does not limit the number of total running servers.
        See active_server_limit for that.

        If more than this many users attempt to spawn at a time, their
        requests will be rejected with a 429 error asking them to try again.
        Users will have to wait for some of the spawning services
        to finish starting before they can start their own.

        If set to 0, no limit is enforced.
        """
    ).tag(config=True)

    active_server_limit = Integer(
        0,
        help="""
        Maximum number of concurrent servers that can be active at a time.

        Setting this can limit the total resources your users can consume.

        An active server is any server that's not fully stopped.
        It is considered active from the time it has been requested
        until the time that it has completely stopped.

        If this many user servers are active, users will not be able to
        launch new servers until a server is shutdown.
        Spawn requests will be rejected with a 429 error asking them to try again.

        If set to 0, no limit is enforced.
        """
    ).tag(config=True)

    db_url = Unicode('sqlite:///jupyterhub.sqlite',
        help="url for the database. e.g. `sqlite:///jupyterhub.sqlite`"
    ).tag(config=True)

    @observe('db_url')
    def _db_url_changed(self, change):
        new = change['new']
        if '://' not in new:
            # assume sqlite, if given as a plain filename
            self.db_url = 'sqlite:///%s' % new

    db_kwargs = Dict(
        help="""Include any kwargs to pass to the database connection.
        See sqlalchemy.create_engine for details.
        """
    ).tag(config=True)

    upgrade_db = Bool(False,
        help="""Upgrade the database automatically on start.

        Only safe if database is regularly backed up.
        Only SQLite databases will be backed up to a local file automatically.
    """).tag(config=True)
    reset_db = Bool(False,
        help="Purge and reset the database."
    ).tag(config=True)
    debug_db = Bool(False,
        help="log all database transactions. This has A LOT of output"
    ).tag(config=True)
    session_factory = Any()

    users = Instance(UserDict)

    @default('users')
    def _users_default(self):
        assert self.tornado_settings
        return UserDict(db_factory=lambda: self.db, settings=self.tornado_settings)

    admin_access = Bool(False,
        help="""Grant admin users permission to access single-user servers.

        Users should be properly informed if this is enabled.
        """
    ).tag(config=True)
    admin_users = Set(
        help="""DEPRECATED since version 0.7.2, use Authenticator.admin_users instead."""
    ).tag(config=True)

    tornado_settings = Dict(
        help="Extra settings overrides to pass to the tornado application."
    ).tag(config=True)

    cleanup_servers = Bool(True,
        help="""Whether to shutdown single-user servers when the Hub shuts down.

        Disable if you want to be able to teardown the Hub while leaving the single-user servers running.

        If both this and cleanup_proxy are False, sending SIGINT to the Hub will
        only shutdown the Hub, leaving everything else running.

        The Hub should be able to resume from database state.
        """
    ).tag(config=True)

    cleanup_proxy = Bool(True,
        help="""Whether to shutdown the proxy when the Hub shuts down.

        Disable if you want to be able to teardown the Hub while leaving the proxy running.

        Only valid if the proxy was starting by the Hub process.

        If both this and cleanup_servers are False, sending SIGINT to the Hub will
        only shutdown the Hub, leaving everything else running.

        The Hub should be able to resume from database state.
        """
    ).tag(config=True)

    statsd_host = Unicode(
        help="Host to send statsd metrics to. An empty string (the default) disables sending metrics."
    ).tag(config=True)

    statsd_port = Integer(
        8125,
        help="Port on which to send statsd metrics about the hub"
    ).tag(config=True)

    statsd_prefix = Unicode(
        'jupyterhub',
        help="Prefix to use for all metrics sent by jupyterhub to statsd"
    ).tag(config=True)

    handlers = List()

    _log_formatter_cls = CoroutineLogFormatter
    http_server = None
    proxy_process = None
    io_loop = None

    @default('log_level')
    def _log_level_default(self):
        return logging.INFO

    @default('log_datefmt')
    def _log_datefmt_default(self):
        """Exclude date from default date format"""
        return "%Y-%m-%d %H:%M:%S"

    @default('log_format')
    def _log_format_default(self):
        """override default log format to include time"""
        return "%(color)s[%(levelname)1.1s %(asctime)s.%(msecs).03d %(name)s %(module)s:%(lineno)d]%(end_color)s %(message)s"

    extra_log_file = Unicode(
        help="""
        DEPRECATED: use output redirection instead, e.g.

        jupyterhub &>> /var/log/jupyterhub.log
        """
    ).tag(config=True)

    @observe('extra_log_file')
    def _log_file_changed(self, change):
        if change.new:
            self.log.warning(dedent("""
                extra_log_file is DEPRECATED in jupyterhub-0.8.2.

                extra_log_file only redirects logs of the Hub itself,
                and will discard any other output, such as
                that of subprocess spawners or the proxy.

                It is STRONGLY recommended that you redirect process
                output instead, e.g.

                    jupyterhub &>> '{}'
            """.format(change.new)))

    extra_log_handlers = List(
        Instance(logging.Handler),
        help="Extra log handlers to set on JupyterHub logger",
    ).tag(config=True)

    statsd = Any(allow_none=False, help="The statsd client, if any. A mock will be used if we aren't using statsd")

    @default('statsd')
    def _statsd(self):
        if self.statsd_host:
            import statsd
            client = statsd.StatsClient(
                self.statsd_host,
                self.statsd_port,
                self.statsd_prefix
            )
            return client
        else:
            # return an empty mock object!
            return EmptyClass()

    def init_logging(self):
        # This prevents double log messages because tornado use a root logger that
        # self.log is a child of. The logging module dipatches log messages to a log
        # and all of its ancenstors until propagate is set to False.
        self.log.propagate = False

        if self.extra_log_file:
            self.extra_log_handlers.append(
                logging.FileHandler(self.extra_log_file)
            )

        _formatter = self._log_formatter_cls(
            fmt=self.log_format,
            datefmt=self.log_datefmt,
        )
        for handler in self.extra_log_handlers:
            if handler.formatter is None:
                handler.setFormatter(_formatter)
            self.log.addHandler(handler)

        # disable curl debug, which is TOO MUCH
        logging.getLogger('tornado.curl_httpclient').setLevel(max(self.log_level, logging.INFO))

        # hook up tornado 3's loggers to our app handlers
        for log in (app_log, access_log, gen_log):
            # ensure all log statements identify the application they come from
            log.name = self.log.name
        logger = logging.getLogger('tornado')
        logger.propagate = True
        logger.parent = self.log
        logger.setLevel(self.log.level)

    def init_ports(self):
        if self.hub_port == self.port:
            raise TraitError("The hub and proxy cannot both listen on port %i" % self.port)

    @staticmethod
    def add_url_prefix(prefix, handlers):
        """add a url prefix to handlers"""
        for i, tup in enumerate(handlers):
            lis = list(tup)
            lis[0] = url_path_join(prefix, tup[0])
            handlers[i] = tuple(lis)
        return handlers

    def init_handlers(self):
        h = []
        # load handlers from the authenticator
        h.extend(self.authenticator.get_handlers(self))
        # set default handlers
        h.extend(handlers.default_handlers)
        h.extend(apihandlers.default_handlers)

        h.append((r'/logo', LogoHandler, {'path': self.logo_file}))
        self.handlers = self.add_url_prefix(self.hub_prefix, h)
        # some extra handlers, outside hub_prefix
        self.handlers.extend([
            # add trailing / to `/hub`
            (self.hub_prefix.rstrip('/'), handlers.AddSlashHandler),
            # add trailing / to ``/user|services/:name`
            (r"%s(user|services)/([^/]+)" % self.base_url, handlers.AddSlashHandler),
            (r"(?!%s).*" % self.hub_prefix, handlers.PrefixRedirectHandler),
            (r'(.*)', handlers.Template404),
        ])

    def _check_db_path(self, path):
        """More informative log messages for failed filesystem access"""
        path = os.path.abspath(path)
        parent, fname = os.path.split(path)
        user = getuser()
        if not os.path.isdir(parent):
            self.log.error("Directory %s does not exist", parent)
        if os.path.exists(parent) and not os.access(parent, os.W_OK):
            self.log.error("%s cannot create files in %s", user, parent)
        if os.path.exists(path) and not os.access(path, os.W_OK):
            self.log.error("%s cannot edit %s", user, path)

    def init_secrets(self):
        trait_name = 'cookie_secret'
        trait = self.traits()[trait_name]
        env_name = trait.metadata.get('env')
        secret_file = os.path.abspath(
            os.path.expanduser(self.cookie_secret_file)
        )
        secret = self.cookie_secret
        secret_from = 'config'
        # load priority: 1. config, 2. env, 3. file
        secret_env = os.environ.get(env_name)
        if not secret and secret_env:
            secret_from = 'env'
            self.log.info("Loading %s from env[%s]", trait_name, env_name)
            secret = binascii.a2b_hex(secret_env)
        if not secret and os.path.exists(secret_file):
            secret_from = 'file'
            self.log.info("Loading %s from %s", trait_name, secret_file)
            try:
                perm = os.stat(secret_file).st_mode
                if perm & 0o07:
                    raise ValueError("cookie_secret_file can be read or written by anybody")
                with open(secret_file) as f:
                    text_secret = f.read().strip()
                if HEX_RE.match(text_secret):
                    # >= 0.8, use 32B hex
                    secret = binascii.a2b_hex(text_secret)
                else:
                    # old b64 secret with a bunch of ignored bytes
                    secret = binascii.a2b_base64(text_secret)
                    self.log.warning(dedent("""
                    Old base64 cookie-secret detected in {0}.

                    JupyterHub >= 0.8 expects 32B hex-encoded cookie secret
                    for tornado's sha256 cookie signing.

                    To generate a new secret:

                        openssl rand -hex 32 > "{0}"
                    """).format(secret_file))
            except Exception as e:
                self.log.error(
                    "Refusing to run JupyterHub with invalid cookie_secret_file. "
                    "%s error was: %s",
                    secret_file, e)
                self.exit(1)

        if not secret:
            secret_from = 'new'
            self.log.debug("Generating new %s", trait_name)
            secret = os.urandom(COOKIE_SECRET_BYTES)

        if secret_file and secret_from == 'new':
            # if we generated a new secret, store it in the secret_file
            self.log.info("Writing %s to %s", trait_name, secret_file)
            text_secret = binascii.b2a_hex(secret).decode('ascii')
            with open(secret_file, 'w') as f:
                f.write(text_secret)
                f.write('\n')
            try:
                os.chmod(secret_file, 0o600)
            except OSError:
                self.log.warning("Failed to set permissions on %s", secret_file)
        # store the loaded trait value
        self.cookie_secret = secret

    def init_db(self):
        """Create the database connection"""

        self.log.debug("Connecting to db: %s", self.db_url)
        if self.upgrade_db:
            dbutil.upgrade_if_needed(self.db_url, log=self.log)

        try:
            self.session_factory = orm.new_session_factory(
                self.db_url,
                reset=self.reset_db,
                echo=self.debug_db,
                **self.db_kwargs
            )
            self.db = self.session_factory()
        except OperationalError as e:
            self.log.error("Failed to connect to db: %s", self.db_url)
            self.log.debug("Database error was:", exc_info=True)
            if self.db_url.startswith('sqlite:///'):
                self._check_db_path(self.db_url.split(':///', 1)[1])
            self.log.critical('\n'.join([
                "If you recently upgraded JupyterHub, try running",
                "    jupyterhub upgrade-db",
                "to upgrade your JupyterHub database schema",
            ]))
            self.exit(1)
        except orm.DatabaseSchemaMismatch as e:
            self.exit(e)

    def init_hub(self):
        """Load the Hub config into the database"""
        self.hub = Hub(
            ip=self.hub_ip,
            port=self.hub_port,
            base_url=self.hub_prefix,
            public_host=self.subdomain_host,
        )
        if self.hub_connect_ip:
            self.hub.connect_ip = self.hub_connect_ip
        if self.hub_connect_port:
            self.hub.connect_port = self.hub_connect_port

    @gen.coroutine
    def init_users(self):
        """Load users into and from the database"""
        db = self.db

        if self.authenticator.enable_auth_state:
            # check that auth_state encryption is available
            # if it's not, exit with an informative error.
            ck = crypto.CryptKeeper.instance()
            try:
                ck.check_available()
            except Exception as e:
                self.exit("auth_state is enabled, but encryption is not available: %s" % e)

        if self.admin_users and not self.authenticator.admin_users:
            self.log.warning(
                "\nJupyterHub.admin_users is deprecated since version 0.7.2."
                "\nUse Authenticator.admin_users instead."
            )
            self.authenticator.admin_users = self.admin_users
        admin_users = [
            self.authenticator.normalize_username(name)
            for name in self.authenticator.admin_users
        ]
        self.authenticator.admin_users = set(admin_users)  # force normalization
        for username in admin_users:
            if not self.authenticator.validate_username(username):
                raise ValueError("username %r is not valid" % username)

        if not admin_users:
            self.log.warning("No admin users, admin interface will be unavailable.")
            self.log.warning("Add any administrative users to `c.Authenticator.admin_users` in config.")

        new_users = []

        for name in admin_users:
            # ensure anyone specified as admin in config is admin in db
            user = orm.User.find(db, name)
            if user is None:
                user = orm.User(name=name, admin=True)
                new_users.append(user)
                db.add(user)
            else:
                user.admin = True

        # the admin_users config variable will never be used after this point.
        # only the database values will be referenced.

        whitelist = [
            self.authenticator.normalize_username(name)
            for name in self.authenticator.whitelist
        ]
        self.authenticator.whitelist = set(whitelist)  # force normalization
        for username in whitelist:
            if not self.authenticator.validate_username(username):
                raise ValueError("username %r is not valid" % username)

        if not whitelist:
            self.log.info("Not using whitelist. Any authenticated user will be allowed.")

        # add whitelisted users to the db
        for name in whitelist:
            user = orm.User.find(db, name)
            if user is None:
                user = orm.User(name=name)
                new_users.append(user)
                db.add(user)

        db.commit()

        # Notify authenticator of all users.
        # This ensures Auth whitelist is up-to-date with the database.
        # This lets whitelist be used to set up initial list,
        # but changes to the whitelist can occur in the database,
        # and persist across sessions.
        for user in db.query(orm.User):
            try:
                yield gen.maybe_future(self.authenticator.add_user(user))
            except Exception:
                self.log.exception("Error adding user %s already in db", user.name)
                if self.authenticator.delete_invalid_users:
                    self.log.warning("Deleting invalid user %s from the Hub database", user.name)
                    db.delete(user)
                else:
                    self.log.warning(dedent("""
                    You can set
                        c.Authenticator.delete_invalid_users = True
                    to automatically delete users from the Hub database that no longer pass
                    Authenticator validation,
                    such as when user accounts are deleted from the external system
                    without notifying JupyterHub.
                    """))
        db.commit()

        # The whitelist set and the users in the db are now the same.
        # From this point on, any user changes should be done simultaneously
        # to the whitelist set and user db, unless the whitelist is empty (all users allowed).

    @gen.coroutine
    def init_groups(self):
        """Load predefined groups into the database"""
        db = self.db
        for name, usernames in self.load_groups.items():
            group = orm.Group.find(db, name)
            if group is None:
                group = orm.Group(name=name)
                db.add(group)
            for username in usernames:
                username = self.authenticator.normalize_username(username)
                if not (yield gen.maybe_future(self.authenticator.check_whitelist(username))):
                    raise ValueError("Username %r is not in whitelist" % username)
                user = orm.User.find(db, name=username)
                if user is None:
                    if not self.authenticator.validate_username(username):
                        raise ValueError("Group username %r is not valid" % username)
                    user = orm.User(name=username)
                    db.add(user)
                group.users.append(user)
        db.commit()

    @gen.coroutine
    def _add_tokens(self, token_dict, kind):
        """Add tokens for users or services to the database"""
        if kind == 'user':
            Class = orm.User
        elif kind == 'service':
            Class = orm.Service
        else:
            raise ValueError("kind must be user or service, not %r" % kind)

        db = self.db
        for token, name in token_dict.items():
            if kind == 'user':
                name = self.authenticator.normalize_username(name)
                if not (yield gen.maybe_future(self.authenticator.check_whitelist(name))):
                    raise ValueError("Token name %r is not in whitelist" % name)
                if not self.authenticator.validate_username(name):
                    raise ValueError("Token name %r is not valid" % name)
            orm_token = orm.APIToken.find(db, token)
            if orm_token is None:
                obj = Class.find(db, name)
                created = False
                if obj is None:
                    created = True
                    self.log.debug("Adding %s %s to database", kind, name)
                    obj = Class(name=name)
                    db.add(obj)
                    db.commit()
                self.log.info("Adding API token for %s: %s", kind, name)
                try:
                    # set generated=False to ensure that user-provided tokens
                    # get extra hashing (don't trust entropy of user-provided tokens)
                    obj.new_api_token(token, generated=self.trust_user_provided_tokens)
                except Exception:
                    if created:
                        # don't allow bad tokens to create users
                        db.delete(obj)
                        db.commit()
                        raise
            else:
                self.log.debug("Not duplicating token %s", orm_token)
        db.commit()

    @gen.coroutine
    def init_api_tokens(self):
        """Load predefined API tokens (for services) into database"""
        yield self._add_tokens(self.service_tokens, kind='service')
        yield self._add_tokens(self.api_tokens, kind='user')

    def init_services(self):
        self._service_map.clear()
        if self.domain:
            domain = 'services.' + self.domain
            parsed = urlparse(self.subdomain_host)
            host = '%s://services.%s' % (parsed.scheme, parsed.netloc)
        else:
            domain = host = ''
        client_store = self.oauth_provider.client_authenticator.client_store
        for spec in self.services:
            if 'name' not in spec:
                raise ValueError('service spec must have a name: %r' % spec)
            name = spec['name']
            # get/create orm
            orm_service = orm.Service.find(self.db, name=name)
            if orm_service is None:
                # not found, create a new one
                orm_service = orm.Service(name=name)
                self.db.add(orm_service)
            orm_service.admin = spec.get('admin', False)
            self.db.commit()
            service = Service(parent=self,
                base_url=self.base_url,
                db=self.db, orm=orm_service,
                domain=domain, host=host,
                hub=self.hub,
            )

            traits = service.traits(input=True)
            for key, value in spec.items():
                if key not in traits:
                    raise AttributeError("No such service field: %s" % key)
                setattr(service, key, value)

            if service.managed:
                if not service.api_token:
                    # generate new token
                    service.api_token = service.orm.new_api_token()
                else:
                    # ensure provided token is registered
                    self.service_tokens[service.api_token] = service.name
            else:
                self.service_tokens[service.api_token] = service.name

            if service.url:
                parsed = urlparse(service.url)
                if parsed.port is not None:
                    port = parsed.port
                elif parsed.scheme == 'http':
                    port = 80
                elif parsed.scheme == 'https':
                    port = 443
                server = service.orm.server = orm.Server(
                    proto=parsed.scheme,
                    ip=parsed.hostname,
                    port=port,
                    cookie_name='jupyterhub-services',
                    base_url=service.prefix,
                )
                self.db.add(server)

                client_store.add_client(
                    client_id=service.oauth_client_id,
                    client_secret=service.api_token,
                    redirect_uri=host + url_path_join(service.prefix, 'oauth_callback'),
                )
            else:
                service.orm.server = None

            self._service_map[name] = service

        # delete services from db not in service config:
        for service in self.db.query(orm.Service):
            if service.name not in self._service_map:
                self.db.delete(service)
        self.db.commit()

    @gen.coroutine
    def check_services_health(self):
        """Check connectivity of all services"""
        for name, service in self._service_map.items():
            if not service.url:
                continue
            try:
                yield Server.from_orm(service.orm.server).wait_up(timeout=1)
            except TimeoutError:
                self.log.warning("Cannot connect to %s service %s at %s", service.kind, name, service.url)
            else:
                self.log.debug("%s service %s running at %s", service.kind.title(), name, service.url)

    @gen.coroutine
    def init_spawners(self):
        db = self.db

        user_summaries = ['']

        def _user_summary(user):
            parts = ['{0: >8}'.format(user.name)]
            if user.admin:
                parts.append('admin')
            for name, spawner in sorted(user.spawners.items(), key=itemgetter(0)):
                if spawner.server:
                    parts.append('%s:%s running at %s' % (user.name, name, spawner.server))
            return ' '.join(parts)

        @gen.coroutine
        def user_stopped(user, server_name):
            spawner = user.spawners[server_name]
            status = yield spawner.poll()
            self.log.warning("User %s server stopped with exit code: %s",
                user.name, status,
            )
            yield self.proxy.delete_user(user, server_name)
            yield user.stop(server_name)

        for orm_user in db.query(orm.User):
            self.users[orm_user.id] = user = User(orm_user, self.tornado_settings)
            self.log.debug("Loading state for %s from db", user.name)
            for name, spawner in user.spawners.items():
                status = 0
                if spawner.server:
                    try:
                        status = yield spawner.poll()
                    except Exception:
                        self.log.exception("Failed to poll spawner for %s, assuming the spawner is not running.",
                            spawner._log_name)
                        status = -1

                if status is None:
                    self.log.info("%s still running", user.name)
                    spawner.add_poll_callback(user_stopped, user, name)
                    spawner.start_polling()
                else:
                    # user not running. This is expected if server is None,
                    # but indicates the user's server died while the Hub wasn't running
                    # if spawner.server is defined.
                    if spawner.server:
                        self.log.warning("%s appears to have stopped while the Hub was down", spawner._log_name)
                        # remove server entry from db
                        db.delete(spawner.orm_spawner.server)
                        spawner.server = None
                    else:
                        self.log.debug("%s not running", spawner._log_name)
            db.commit()

            user_summaries.append(_user_summary(user))

        self.log.debug("Loaded users: %s", '\n'.join(user_summaries))
        db.commit()

    def init_oauth(self):
        base_url = self.hub.base_url
        self.oauth_provider = make_provider(
            lambda : self.db,
            url_prefix=url_path_join(base_url, 'api/oauth2'),
            login_url=url_path_join(base_url, 'login')
        )

    def init_proxy(self):
        """Load the Proxy config"""
        # FIXME: handle deprecated config here
        public_url = 'http{s}://{ip}:{port}{base_url}'.format(
            s='s' if self.ssl_cert else '',
            ip=self.ip,
            port=self.port,
            base_url=self.base_url,
        )
        self.proxy = self.proxy_class(
            db_factory=lambda: self.db,
            public_url=public_url,
            parent=self,
            app=self,
            log=self.log,
            hub=self.hub,
            host_routing=bool(self.subdomain_host),
            ssl_cert=self.ssl_cert,
            ssl_key=self.ssl_key,
        )

    def init_tornado_settings(self):
        """Set up the tornado settings dict."""
        base_url = self.hub.base_url
        jinja_options = dict(
            autoescape=True,
        )
        jinja_options.update(self.jinja_environment_options)
        jinja_env = Environment(
            loader=FileSystemLoader(self.template_paths),
            **jinja_options
        )

        login_url = url_path_join(base_url, 'login')
        logout_url = self.authenticator.logout_url(base_url)

        # if running from git, disable caching of require.js
        # otherwise cache based on server start time
        parent = os.path.dirname(os.path.dirname(jupyterhub.__file__))
        if os.path.isdir(os.path.join(parent, '.git')):
            version_hash = ''
        else:
            version_hash = datetime.now().strftime("%Y%m%d%H%M%S")

        settings = dict(
            log_function=log_request,
            config=self.config,
            log=self.log,
            db=self.db,
            proxy=self.proxy,
            hub=self.hub,
            admin_users=self.authenticator.admin_users,
            admin_access=self.admin_access,
            authenticator=self.authenticator,
            spawner_class=self.spawner_class,
            base_url=self.base_url,
            cookie_secret=self.cookie_secret,
            cookie_max_age_days=self.cookie_max_age_days,
            login_url=login_url,
            logout_url=logout_url,
            static_path=os.path.join(self.data_files_path, 'static'),
            static_url_prefix=url_path_join(self.hub.base_url, 'static/'),
            static_handler_class=CacheControlStaticFilesHandler,
            template_path=self.template_paths,
            jinja2_env=jinja_env,
            version_hash=version_hash,
            subdomain_host=self.subdomain_host,
            domain=self.domain,
            statsd=self.statsd,
            allow_named_servers=self.allow_named_servers,
            oauth_provider=self.oauth_provider,
            concurrent_spawn_limit=self.concurrent_spawn_limit,
            active_server_limit=self.active_server_limit,
        )
        # allow configured settings to have priority
        settings.update(self.tornado_settings)
        self.tornado_settings = settings
        # constructing users requires access to tornado_settings
        self.tornado_settings['users'] = self.users
        self.tornado_settings['services'] = self._service_map

    def init_tornado_application(self):
        """Instantiate the tornado Application object"""
        self.tornado_application = web.Application(self.handlers, **self.tornado_settings)

    def init_pycurl(self):
        """Configure tornado to use pycurl by default, if available"""
        # use pycurl by default, if available:
        try:
            AsyncHTTPClient.configure("tornado.curl_httpclient.CurlAsyncHTTPClient")
        except ImportError as e:
            self.log.debug("Could not load pycurl: %s\npycurl is recommended if you have a large number of users.", e)

    def write_pid_file(self):
        pid = os.getpid()
        if self.pid_file:
            self.log.debug("Writing PID %i to %s", pid, self.pid_file)
            with open(self.pid_file, 'w') as f:
                f.write('%i' % pid)

    @gen.coroutine
    @catch_config_error
    def initialize(self, *args, **kwargs):
        super().initialize(*args, **kwargs)
        if self.generate_config or self.subapp:
            return
        self.load_config_file(self.config_file)
        self.init_logging()
        if 'JupyterHubApp' in self.config:
            self.log.warning("Use JupyterHub in config, not JupyterHubApp. Outdated config:\n%s",
                '\n'.join('JupyterHubApp.{key} = {value!r}'.format(key=key, value=value)
                    for key, value in self.config.JupyterHubApp.items()
                )
            )
            cfg = self.config.copy()
            cfg.JupyterHub.merge(cfg.JupyterHubApp)
            self.update_config(cfg)
        self.write_pid_file()
        self.init_pycurl()
        self.init_ports()
        self.init_secrets()
        self.init_db()
        self.init_hub()
        self.init_proxy()
        self.init_oauth()
        yield self.init_users()
        yield self.init_groups()
        self.init_services()
        yield self.init_api_tokens()
        self.init_tornado_settings()
        yield self.init_spawners()
        self.init_handlers()
        self.init_tornado_application()

    @gen.coroutine
    def cleanup(self):
        """Shutdown managed services and various subprocesses. Cleanup runtime files."""

        futures = []

        managed_services = [ s for s in self._service_map.values() if s.managed ]
        if managed_services:
            self.log.info("Cleaning up %i services...", len(managed_services))
            for service in managed_services:
                futures.append(service.stop())

        if self.cleanup_servers:
            self.log.info("Cleaning up single-user servers...")
            # request (async) process termination
            for uid, user in self.users.items():
                for name, spawner in user.spawners.items():
                    if spawner.active:
                        futures.append(user.stop(name))
        else:
            self.log.info("Leaving single-user servers running")

        # clean up proxy while single-user servers are shutting down
        if self.cleanup_proxy:
            if self.proxy.should_start:
                yield gen.maybe_future(self.proxy.stop())
            else:
                self.log.info("I didn't start the proxy, I can't clean it up")
        else:
            self.log.info("Leaving proxy running")

        # wait for the requests to stop finish:
        for f in futures:
            try:
                yield f
            except Exception as e:
                self.log.error("Failed to stop user: %s", e)

        self.db.commit()

        if self.pid_file and os.path.exists(self.pid_file):
            self.log.info("Cleaning up PID file %s", self.pid_file)
            os.remove(self.pid_file)

        # finally stop the loop once we are all cleaned up
        self.log.info("...done")

    def write_config_file(self):
        """Write our default config to a .py config file"""
        config_file_dir = os.path.dirname(os.path.abspath(self.config_file))
        if not os.path.isdir(config_file_dir):
            self.exit("{} does not exist. The destination directory must exist before generating config file.".format(
                config_file_dir,
            ))
        if os.path.exists(self.config_file) and not self.answer_yes:
            answer = ''

            def ask():
                prompt = "Overwrite %s with default config? [y/N]" % self.config_file
                try:
                    return input(prompt).lower() or 'n'
                except KeyboardInterrupt:
                    print('')  # empty line
                    return 'n'
            answer = ask()
            while not answer.startswith(('y', 'n')):
                print("Please answer 'yes' or 'no'")
                answer = ask()
            if answer.startswith('n'):
                return

        config_text = self.generate_config_file()
        if isinstance(config_text, bytes):
            config_text = config_text.decode('utf8')
        print("Writing default config to: %s" % self.config_file)
        with open(self.config_file, mode='w') as f:
            f.write(config_text)

    @gen.coroutine
    def update_last_activity(self):
        """Update User.last_activity timestamps from the proxy"""
        routes = yield self.proxy.get_all_routes()
        users_count = 0
        active_users_count = 0
        now = datetime.utcnow()
        for prefix, route in routes.items():
            route_data = route['data']
            if 'user' not in route_data:
                # not a user route, ignore it
                continue
            if 'server_name' not in route_data:
                continue
            users_count += 1
            if 'last_activity' not in route_data:
                # no last activity data (possibly proxy other than CHP)
                continue
            user = orm.User.find(self.db, route_data['user'])
            if user is None:
                self.log.warning("Found no user for route: %s", route)
                continue
            spawner = user.orm_spawners.get(route_data['server_name'])
            if spawner is None:
                self.log.warning("Found no spawner for route: %s", route)
                continue
            try:
                dt = datetime.strptime(route_data['last_activity'], ISO8601_ms)
            except Exception:
                dt = datetime.strptime(route_data['last_activity'], ISO8601_s)
            user.last_activity = max(user.last_activity, dt)
            spawner.last_activity = max(spawner.last_activity, dt)
            # FIXME: Make this configurable duration. 30 minutes for now!
            if (now - user.last_activity).total_seconds() < 30 * 60:
                active_users_count += 1
        self.statsd.gauge('users.running', users_count)
        self.statsd.gauge('users.active', active_users_count)

        self.db.commit()
        yield self.proxy.check_routes(self.users, self._service_map, routes)

    @gen.coroutine
    def start(self):
        """Start the whole thing"""
        self.io_loop = loop = IOLoop.current()

        if self.subapp:
            self.subapp.start()
            loop.stop()
            return

        if self.generate_config:
            self.write_config_file()
            loop.stop()
            return

        # start the webserver
        self.http_server = tornado.httpserver.HTTPServer(self.tornado_application, xheaders=True)
        try:
            self.http_server.listen(self.hub_port, address=self.hub_ip)
        except Exception:
            self.log.error("Failed to bind hub to %s", self.hub.bind_url)
            raise
        else:
            self.log.info("Hub API listening on %s", self.hub.bind_url)

        # start the proxy
        if self.proxy.should_start:
            try:
                yield self.proxy.start()
            except Exception as e:
                self.log.critical("Failed to start proxy", exc_info=True)
                self.exit(1)
        else:
            self.log.info("Not starting proxy")

        # start the service(s)
        for service_name, service in self._service_map.items():
            msg = '%s at %s' % (service_name, service.url) if service.url else service_name
            if service.managed:
                self.log.info("Starting managed service %s", msg)
                try:
                    service.start()
                except Exception as e:
                    self.log.critical("Failed to start service %s", service_name, exc_info=True)
                    self.exit(1)
            else:
                self.log.info("Adding external service %s", msg)

            if service.url:
                tries = 10 if service.managed else 1
                for i in range(tries):
                    try:
                        yield Server.from_orm(service.orm.server).wait_up(http=True, timeout=1)
                    except TimeoutError:
                        if service.managed:
                            status = yield service.spawner.poll()
                            if status is not None:
                                self.log.error("Service %s exited with status %s", service_name, status)
                                break
                    else:
                        break
                else:
                    self.log.error("Cannot connect to %s service %s at %s. Is it running?", service.kind, service_name, service.url)

        yield self.proxy.check_routes(self.users, self._service_map)


        if self.service_check_interval and any(s.url for s in self._service_map.values()):
            pc = PeriodicCallback(self.check_services_health, 1e3 * self.service_check_interval)
            pc.start()

        if self.last_activity_interval:
            pc = PeriodicCallback(self.update_last_activity, 1e3 * self.last_activity_interval)
            self.last_activity_callback = pc
            pc.start()

        self.log.info("JupyterHub is now running at %s", self.proxy.public_url)
        # register cleanup on both TERM and INT
        atexit.register(self.atexit)
        self.init_signal()

    def init_signal(self):
        signal.signal(signal.SIGTERM, self.sigterm)

    def sigterm(self, signum, frame):
        self.log.critical("Received SIGTERM, shutting down")
        self.io_loop.stop()
        self.atexit()

    _atexit_ran = False

    def atexit(self):
        """atexit callback"""
        if self._atexit_ran:
            return
        self._atexit_ran = True
        # run the cleanup step (in a new loop, because the interrupted one is unclean)
        IOLoop.clear_current()
        loop = IOLoop()
        loop.make_current()
        loop.run_sync(self.cleanup)

    def stop(self):
        if not self.io_loop:
            return
        if self.http_server:
            self.http_server.stop()
        self.io_loop.add_callback(self.io_loop.stop)

    @gen.coroutine
    def launch_instance_async(self, argv=None):
        try:
            yield self.initialize(argv)
            yield self.start()
        except Exception as e:
            self.log.exception("")
            self.exit(1)

    @classmethod
    def launch_instance(cls, argv=None):
        self = cls.instance()
        loop = IOLoop.current()
        loop.add_callback(self.launch_instance_async, argv)
        try:
            loop.start()
        except KeyboardInterrupt:
            print("\nInterrupted")


NewToken.classes.append(JupyterHub)
UpgradeDB.classes.append(JupyterHub)

main = JupyterHub.launch_instance

if __name__ == "__main__":
    main()