# -*- coding: utf-8 -*-
# linux
# Copyright (C) 2013-2017 LEAP
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

"""
Linux VPN launcher implementation.
"""

import os

import psutil
import subprocess

from twisted.internet import defer, reactor
from twisted.internet.endpoints import clientFromString, connectProtocol
from twisted.logger import Logger

from leap.bitmask.system import IS_SNAP
from leap.bitmask.vpn.utils import first, force_eval
from leap.bitmask.vpn import constants
from leap.bitmask.vpn import _config
from leap.bitmask.vpn.privilege import LinuxPolicyChecker
from leap.bitmask.vpn.management import ManagementProtocol
from leap.bitmask.vpn.launcher import VPNLauncher

TERMINATE_MAXTRIES = 10
TERMINATE_WAIT = 1  # secs
RESTART_WAIT = 2  # secs

log = Logger()


class OpenVPNAlreadyRunning(Exception):
    message = ("Another openvpn instance is already running, and could "
               "not be stopped.")


class AlienOpenVPNAlreadyRunning(Exception):
    message = ("Another openvpn instance is already running, and could "
               "not be stopped because it was not launched by LEAP.")


def _maybe_get_running_openvpn():
    """
    Looks for previously running openvpn instances.

    :rtype: psutil Process
    """
    openvpn = None
    for p in psutil.process_iter():
        try:
            # This needs more work, see #3268, but for the moment
            # we need to be able to filter out arguments in the form
            # --openvpn-foo, since otherwise we are shooting ourselves
            # in the feet.

            cmdline = p.cmdline()
            if any(map(lambda s: s.find(
                    "LEAPOPENVPN") != -1, cmdline)):
                openvpn = p
                break
        except psutil.AccessDenied:
            pass
    return openvpn


class LinuxVPNLauncher(VPNLauncher):

    # The following classes depend on force_eval to be called against
    # the classes, to get the evaluation of the standalone flag on runtine.
    # If we keep extending this kind of classes, we should abstract the
    # handling of the STANDALONE flag in a base class

    class BITMASK_ROOT(object):
        def __call__(self):
            current_version = self._version(_config.get_bitmask_helper_path())
            _sys = constants.BITMASK_ROOT_SYSTEM
            _sys_version = 0
            _local = constants.BITMASK_ROOT_LOCAL
            _local_version = 0
            _snap = constants.BITMASK_ROOT_SNAP
            _snap_version = 0

            if IS_SNAP:
                return _snap

            if os.path.isfile(_sys):
                _sys_version = self._version(_sys)

            if os.path.isfile(_local):
                _local_version = self._version(_local)

            if _sys_version == current_version:
                return _sys
            elif _local_version == current_version:
                return _local
            elif _sys_version != 0 and _sys_version >= _local_version:
                return _sys
            elif _local_version != 0:
                return _local
            else:
                return 'bitmask-root'

        def _version(self, bitmask_root):
            # FIXME this, as a couple of other calls in the vpn modules, relies
            # on having a python executable in the path. Even all modern
            # default distros provide that, we should not rely on it.
            # At least, we should be ready to do error handling if the binary
            # is not found.
            out = subprocess.check_output(['python', bitmask_root, "version"])
            return int(out)

    class OPENVPN_BIN_PATH(object):
        def __call__(self):

            if IS_SNAP:
                # this should change when bitmask is also a snap. for now,
                # snap means RiseupVPN
                return constants.OPENVPN_SNAP

            _sys = constants.OPENVPN_SYSTEM
            _local = constants.OPENVPN_LOCAL
            # XXX this implies that, for the time being, we prefer the system
            # openvpn if there is any. We assume that the system is kept
            # up-to-date, since we still do not have a safe way of upgrading
            # the bundle binaries. See #9101
            if os.path.exists(_sys):
                return _sys
            else:
                return _local

    class POLKIT_PATH(object):
        def __call__(self):
            # LinuxPolicyChecker will give us the right path if standalone.
            return LinuxPolicyChecker.get_polkit_path()

    OTHER_FILES = (POLKIT_PATH, BITMASK_ROOT, OPENVPN_BIN_PATH)

    @classmethod
    def get_vpn_command(kls, vpnconfig, providerconfig, socket_host,
                        remotes, socket_port="unix", openvpn_verb=1):
        """
        Returns the Linux implementation for the vpn launching command.

        Might raise:
            NoPkexecAvailable,
            NoPolkitAuthAgentAvailable,
            OpenVPNNotFoundException,
            VPNLauncherException.

        :param vpnconfig: vpn configuration object
        :type vpnconfig: VPNConfig
        :param providerconfig: provider specific configuration
        :type providerconfig: ProviderConfig
        :param socket_host: either socket path (unix) or socket IP
        :type socket_host: str
        :param socket_port: either string "unix" if it's a unix socket,
                            or port otherwise
        :type socket_port: str
        :param openvpn_verb: the openvpn verbosity wanted
        :type openvpn_verb: int

        :return: A VPN command ready to be launched.
        :rtype: list
        """
        command = []
        # we use `super` in order to send the class to use
        command = super(LinuxVPNLauncher, kls).get_vpn_command(
            vpnconfig, providerconfig, socket_host, socket_port, remotes,
            openvpn_verb)

        if IS_SNAP:
            # cannot reference bitmask_root because 'local variable command
            # referenced before assignment' XXX bug!
            # this should change when bitmask is also a snap. for now,
            # snap means RiseupVPN
            return ["pkexec", constants.BITMASK_ROOT_SNAP,
                    "openvpn", "start"] + command

        bitmask_root = force_eval(kls.BITMASK_ROOT)
        command.insert(0, bitmask_root)
        command.insert(1, "openvpn")
        command.insert(2, "start")

        # this is a workaround for integration tests, since it's not
        # trivial to run polkit inside docker containers.
        # however, you might want to run bitmask as root under certain
        # environments, like embedded devices.
        if os.getuid() != 0:
            policyChecker = LinuxPolicyChecker()
            pkexec = policyChecker.get_usable_pkexec()
            if pkexec:
                command.insert(0, first(pkexec))
        return command

    def terminate_or_kill(self, terminatefun, killfun, proc):
        terminatefun()

        # we trigger a countdown to be unpolite
        # if strictly needed.
        d = defer.Deferred()
        reactor.callLater(
            TERMINATE_WAIT, self._wait_and_kill, killfun, proc, d)
        return d

    def _wait_and_kill(self, killfun, proc, deferred, tries=0):
        """
        Check if the process is still alive, and call the killfun
        after waiting several times during a timeout period.

        :param tries: counter of tries, used in recursion
        :type tries: int
        """
        if tries < TERMINATE_MAXTRIES:
            if proc.transport and proc.transport.pid is None:
                deferred.callback(True)
                return
            else:
                log.debug('Process did not die, waiting...')

            tries += 1
            reactor.callLater(
                TERMINATE_WAIT,
                self._wait_and_kill, killfun, proc, deferred, tries)
            return

        # after running out of patience, we try a killProcess
        d = killfun()
        d.addCallback(lambda _: deferred.callback(True))
        return d

    def kill_previous_openvpn(kls):
        """
        Checks if VPN is already running and tries to stop it.

        Might raise OpenVPNAlreadyRunning.

        :return: a deferred, that fires with True if stopped.
        """
        @defer.inlineCallbacks
        def gotProtocol(proto):
            return proto.signal('SIGTERM')

        def connect_to_management(path):
            # XXX this has a problem with connections to different
            # remotes. So the reconnection will only work when we are
            # terminating instances left running for the same provider.
            # If we are killing an openvpn instance configured for another
            # provider, we will get:
            # TLS Error: local/remote TLS keys are out of sync
            # However, that should be a rare case right now.
            endpoint = clientFromString(reactor, path)
            d = connectProtocol(endpoint, ManagementProtocol(verbose=False))
            d.addCallback(gotProtocol)
            return d

        def verify_termination(ignored):
            openvpn = _maybe_get_running_openvpn()
            if openvpn is None:
                log.debug('Successfully finished already running '
                          'openvpn process.')
                return True
            else:
                log.warn('Unable to terminate OpenVPN')
                raise OpenVPNAlreadyRunning

        openvpn = _maybe_get_running_openvpn()
        if not openvpn:
            log.debug('Could not find openvpn process while '
                      'trying to stop it.')
            return False

        log.debug('OpenVPN is already running, trying to stop it...')
        cmdline = openvpn.cmdline
        management = "--management"

        if isinstance(cmdline, list) and management in cmdline:
            # we know that our invocation has this distinctive fragment, so
            # we use this fingerprint to tell other invocations apart.
            # this might break if we change the configuration path in the
            # launchers

            def smellslikeleap(s):
                return "leap" in s and "providers" in s

            if not any(map(smellslikeleap, cmdline)):
                log.debug("We cannot stop this instance since we do not "
                          "recognise it as a leap invocation.")
                raise AlienOpenVPNAlreadyRunning

            try:
                index = cmdline.index(management)
                host = cmdline[index + 1]
                port = cmdline[index + 2]
                log.debug("Trying to connect to %s:%s"
                          % (host, port))

                if port == 'unix':
                    path = b"unix:path=%s" % host
                d = connect_to_management(path)
                d.addCallback(verify_termination)
                return d

            except (Exception, AssertionError):
                log.failure('Problem trying to terminate OpenVPN')
        else:
            log.debug('Could not find the expected openvpn command line.')