import io
import logging
import os.path
import socket
import threading
import traceback
import uuid
import weakref
import paramiko
import tornado.gen
import tornado.ioloop
import tornado.web
import tornado.websocket
from tornado.concurrent import Future
from tornado.ioloop import IOLoop
from tornado.iostream import _ERRNO_CONNRESET
from tornado.options import define, options, parse_command_line
from tornado.util import errno_from_exception


define('address', default='127.0.0.1', help='listen address')
define('port', default=8888, help='listen port', type=int)
define('debug', default=False, help='debug mode', type=bool)
define('policy', default='warning',
       help='missing host key policy, reject|autoadd|warning')
define('period', default=10, help='seconds for periodic callback', type=int)


BUF_SIZE = 1024
DELAY = 3
workers = {}


class Worker(object):
    def __init__(self, ssh, chan, dst_addr):
        self.loop = IOLoop.current()
        self.ssh = ssh
        self.chan = chan
        self.dst_addr = dst_addr
        self.fd = chan.fileno()
        self.id = str(id(self))
        self.data_to_dst = []
        self.handler = None
        self.mode = IOLoop.READ

    def __call__(self, fd, events):
        if events & IOLoop.READ:
            self.on_read()
        if events & IOLoop.WRITE:
            self.on_write()
        if events & IOLoop.ERROR:
            self.close()

    def set_handler(self, handler):
        if not self.handler:
            self.handler = handler

    def update_handler(self, mode):
        if self.mode != mode:
            self.loop.update_handler(self.fd, mode)
            self.mode = mode

    def on_read(self):
        logging.debug('worker {} on read'.format(self.id))
        try:
            data = self.chan.recv(BUF_SIZE)
        except (OSError, IOError) as e:
            logging.error(e)
            if errno_from_exception(e) in _ERRNO_CONNRESET:
                self.close()
        else:
            logging.debug('"{}" from {}:{}'.format(data, *self.dst_addr))
            if not data:
                self.close()
                return

            logging.debug('"{}" to {}:{}'.format(data, *self.handler.src_addr))
            try:
                self.handler.write_message(data)
            except tornado.websocket.WebSocketClosedError:
                self.close()

    def on_write(self):
        logging.debug('worker {} on write'.format(self.id))
        if not self.data_to_dst:
            return

        data = ''.join(self.data_to_dst)
        logging.debug('"{}" to {}:{}'.format(data, *self.dst_addr))

        try:
            sent = self.chan.send(data)
        except (OSError, IOError) as e:
            logging.error(e)
            if errno_from_exception(e) in _ERRNO_CONNRESET:
                self.close()
            else:
                self.update_handler(IOLoop.WRITE)
        else:
            self.data_to_dst = []
            data = data[sent:]
            if data:
                self.data_to_dst.append(data)
                self.update_handler(IOLoop.WRITE)
            else:
                self.update_handler(IOLoop.READ)

    def close(self):
        logging.debug('Closing worker {}'.format(self.id))
        if self.handler:
            self.loop.remove_handler(self.fd)
            self.handler.close()
        self.chan.close()
        self.ssh.close()
        logging.info('Connection to {}:{} lost'.format(*self.dst_addr))


class MixinHandler(object):

    def __init__(self, *args, **kwargs):
        super(MixinHandler, self).__init__(*args, **kwargs)

    def get_client_addr(self):
        ip = self.request.headers.get('X-Real-Ip')
        port = self.request.headers.get('X-Real-Port')
        addr = None

        if ip and port:
            addr = (ip, int(port))
        elif ip or port:
            logging.warn('Wrong nginx configuration.')

        return addr


class IndexHandler(MixinHandler, tornado.web.RequestHandler):

    def get_privatekey(self):
        try:
            data = self.request.files.get('privatekey')[0]['body']
        except TypeError:
            return
        return data.decode('utf-8')

    def get_specific_pkey(self, pkeycls, privatekey, password):
        logging.info('Trying {}'.format(pkeycls.__name__))
        try:
            pkey = pkeycls.from_private_key(io.StringIO(privatekey),
                                            password=password)
        except paramiko.PasswordRequiredException:
            raise ValueError('Need password to decrypt the private key.')
        except paramiko.SSHException:
            pass
        else:
            return pkey

    def get_pkey(self, privatekey, password):
        password = password.encode('utf-8') if password else None

        pkey = self.get_specific_pkey(paramiko.RSAKey, privatekey, password)\
            or self.get_specific_pkey(paramiko.DSSKey, privatekey, password)\
            or self.get_specific_pkey(paramiko.ECDSAKey, privatekey, password)\
            or self.get_specific_pkey(paramiko.Ed25519Key, privatekey,
                                      password)
        if not pkey:
            raise ValueError('Not a valid private key file or '
                             'wrong password for decrypting the private key.')
        return pkey

    def get_port(self):
        value = self.get_value('port')
        try:
            port = int(value)
        except ValueError:
            port = 0

        if 0 < port < 65536:
            return port

        raise ValueError('Invalid port {}'.format(value))

    def get_value(self, name):
        value = self.get_argument(name)
        if not value:
            raise ValueError('Empty {}'.format(name))
        return value

    def get_args(self):
        hostname = self.get_value('hostname')
        port = self.get_port()
        username = self.get_value('username')
        password = self.get_argument('password')
        privatekey = self.get_privatekey()
        pkey = self.get_pkey(privatekey, password) if privatekey else None
        args = (hostname, port, username, password, pkey)
        logging.debug(args)
        return args

    def get_client_addr(self):
        return super(IndexHandler, self).get_client_addr() or self.request.\
                connection.stream.socket.getpeername()

    def ssh_connect(self):
        ssh = paramiko.SSHClient()
        ssh._system_host_keys = self.settings['system_host_keys']
        ssh._host_keys = self.settings['host_keys']
        ssh.set_missing_host_key_policy(self.settings['policy'])

        args = self.get_args()
        dst_addr = (args[0], args[1])
        logging.info('Connecting to {}:{}'.format(*dst_addr))

        try:
            ssh.connect(*args, timeout=6)
        except socket.error:
            raise ValueError('Unable to connect to {}:{}'.format(*dst_addr))
        except paramiko.BadAuthenticationType:
            raise ValueError('Authentication failed.')
        except paramiko.BadHostKeyException:
            raise ValueError('Bad host key.')

        chan = ssh.invoke_shell(term='xterm')
        chan.setblocking(0)
        worker = Worker(ssh, chan, dst_addr)
        worker.src_addr = self.get_client_addr()
        return worker

    def ssh_connect_wrapped(self, future):
        try:
            worker = self.ssh_connect()
        except Exception as exc:
            logging.error(traceback.format_exc())
            future.set_exception(exc)
        else:
            future.set_result(worker)

    def get(self):
        self.render('index.html')

    @tornado.gen.coroutine
    def post(self):
        worker_id = None
        status = None

        future = Future()
        t = threading.Thread(target=self.ssh_connect_wrapped, args=(future,))
        t.setDaemon(True)
        t.start()

        try:
            worker = yield future
        except Exception as exc:
            status = str(exc)
        else:
            worker_id = worker.id
            workers[worker_id] = worker
            IOLoop.current().call_later(DELAY, recycle, worker)

        self.write(dict(id=worker_id, status=status))


class WsockHandler(MixinHandler, tornado.websocket.WebSocketHandler):

    def __init__(self, *args, **kwargs):
        self.loop = IOLoop.current()
        self.worker_ref = None
        super(WsockHandler, self).__init__(*args, **kwargs)

    def get_client_addr(self):
        return super(WsockHandler, self).get_client_addr() or self.stream.\
                socket.getpeername()

    def open(self):
        self.src_addr = self.get_client_addr()
        logging.info('Connected from {}:{}'.format(*self.src_addr))
        worker = workers.get(self.get_argument('id'))
        if worker and worker.src_addr[0] == self.src_addr[0]:
            workers.pop(worker.id)
            self.set_nodelay(True)
            worker.set_handler(self)
            self.worker_ref = weakref.ref(worker)
            self.loop.add_handler(worker.fd, worker, IOLoop.READ)
        else:
            self.close()

    def on_message(self, message):
        logging.debug('"{}" from {}:{}'.format(message, *self.src_addr))
        worker = self.worker_ref()
        worker.data_to_dst.append(message)
        worker.on_write()

    def on_close(self):
        logging.info('Disconnected from {}:{}'.format(*self.src_addr))
        worker = self.worker_ref() if self.worker_ref else None
        if worker:
            worker.close()


def recycle(worker):
    if worker.handler:
        return
    logging.debug('Recycling worker {}'.format(worker.id))
    workers.pop(worker.id, None)
    worker.close()


def get_host_keys(path):
    if os.path.exists(path) and os.path.isfile(path):
        return paramiko.hostkeys.HostKeys(filename=path)
    return paramiko.hostkeys.HostKeys()


def save_host_keys(host_keys, filename):
    length = len(host_keys)
    if length != host_keys._last_len:
        logging.info('Updating {}'.format(filename))
        host_keys.save(filename)
        host_keys._last_len = length


def get_policy_class(policy):
    origin_policy = policy
    policy = policy.lower()
    if not policy.endswith('policy'):
        policy += 'policy'

    dic = {k.lower(): v for k, v in vars(paramiko.client).items() if type(v)
           is type and issubclass(v, paramiko.client.MissingHostKeyPolicy)}
    try:
        cls = dic[policy]
    except KeyError:
        raise ValueError('Unknown policy {!r}'.format(origin_policy))
    return cls


def get_application_settings():
    base_dir = os.path.dirname(__file__)
    filename = os.path.join(base_dir, 'known_hosts')
    host_keys = get_host_keys(filename)
    system_host_keys = get_host_keys(os.path.expanduser('~/.ssh/known_hosts'))
    policy_class = get_policy_class(options.policy)
    logging.info(policy_class.__name__)

    if policy_class is paramiko.client.AutoAddPolicy:
        host_keys.save(filename)  # for permission test
        host_keys._last_len = len(host_keys)
        tornado.ioloop.PeriodicCallback(
            lambda: save_host_keys(host_keys, filename),
            options.period * 1000  # milliseconds
        ).start()
    elif policy_class is paramiko.client.RejectPolicy:
        if not host_keys and not system_host_keys:
            raise ValueError('Empty known_hosts with reject policy?')

    settings = dict(
        template_path=os.path.join(base_dir, 'templates'),
        static_path=os.path.join(base_dir, 'static'),
        cookie_secret=uuid.uuid4().hex,
        xsrf_cookies=True,
        host_keys=host_keys,
        system_host_keys=system_host_keys,
        policy=policy_class(),
        debug=options.debug
    )

    return settings


def main():
    parse_command_line()
    settings = get_application_settings()

    handlers = [
        (r'/',   IndexHandler),
        (r'/ws', WsockHandler)
    ]

    app = tornado.web.Application(handlers, **settings)
    app.listen(options.port, options.address)
    logging.info('Listening on {}:{}'.format(options.address, options.port))
    IOLoop.current().start()


if __name__ == '__main__':
    main()