#
# The Qubes OS Project, https://www.qubes-os.org/
#
# Copyright (C) 2010-2016  Joanna Rutkowska <joanna@invisiblethingslab.com>
# Copyright (C) 2015-2016  Wojtek Porczyk <woju@invisiblethingslab.com>
# Copyright (C) 2016       Bahtiar `kalkin-` Gadimov <bahtiar@gadimov.de>
#
# This library is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 2.1 of the License, or (at your option) any later version.
#
# This library 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
# Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with this library; if not, see <https://www.gnu.org/licenses/>.
#

'''API for various types of devices.

Main concept is that some domain main
expose (potentially multiple) devices, which can be attached to other domains.
Devices can be of different buses (like 'pci', 'usb', etc). Each device
bus is implemented by an extension.

Devices are identified by pair of (backend domain, `ident`), where `ident` is
:py:class:`str` and can contain only characters from `[a-zA-Z0-9._-]` set.

Such extension should provide:
 - `qubes.devices` endpoint - a class descendant from
 :py:class:`qubes.devices.DeviceInfo`, designed to hold device description (
 including bus-specific properties)
 - handle `device-attach:bus` and `device-detach:bus` events for
 performing the attach/detach action; events are fired even when domain isn't
 running and extension should be prepared for this; handlers for those events
 can be coroutines
 - handle `device-list:bus` event - list devices exposed by particular
 domain; it should return list of appropriate DeviceInfo objects
 - handle `device-get:bus` event - get one device object exposed by this
 domain of given identifier
 - handle `device-list-attached:class` event - list currently attached
 devices to this domain
 - fire `device-list-change:class` event when device list change is detected
 (new/removed device)

Note that device-listing event handlers can not be asynchronous. This for
example means you can not call qrexec service there. This is intentional to
keep device listing operation cheap. You need to design the extension to take
this into account (for example by using QubesDB).

Extension may use QubesDB watch API (QubesVM.watch_qdb_path(path), then handle
`domain-qdb-change:path`) to detect changes and fire
`device-list-change:class` event.
'''
import asyncio

import qubes.utils

class DeviceNotAttached(qubes.exc.QubesException, KeyError):
    '''Trying to detach not attached device'''

class DeviceAlreadyAttached(qubes.exc.QubesException, KeyError):
    '''Trying to attach already attached device'''

class DeviceInfo:
    ''' Holds all information about a device '''
    # pylint: disable=too-few-public-methods
    def __init__(self, backend_domain, ident, description=None,
                 frontend_domain=None):
        #: domain providing this device
        self.backend_domain = backend_domain
        #: device identifier (unique for given domain and device type)
        self.ident = ident
        # allow redefining those as dynamic properties in subclasses
        try:
            #: human readable description/name of the device
            self.description = description
        except AttributeError:
            pass
        try:
            #: (running) domain to which device is currently attached
            self.frontend_domain = frontend_domain
        except AttributeError:
            pass

        if hasattr(self, 'regex'):
            # pylint: disable=no-member
            dev_match = self.regex.match(ident)
            if not dev_match:
                raise ValueError('Invalid device identifier: {!r}'.format(
                    ident))

            for group in self.regex.groupindex:
                setattr(self, group, dev_match.group(group))

    def __hash__(self):
        return hash((self.backend_domain, self.ident))

    def __eq__(self, other):
        return (
            self.backend_domain == other.backend_domain and
            self.ident == other.ident
        )

    def __lt__(self, other):
        if isinstance(other, DeviceInfo):
            return (self.backend_domain, self.ident) < \
                   (other.backend_domain, other.ident)
        return NotImplemented

    def __str__(self):
        return '{!s}:{!s}'.format(self.backend_domain, self.ident)


class DeviceAssignment: # pylint: disable=too-few-public-methods
    ''' Maps a device to a frontend_domain. '''

    def __init__(self, backend_domain, ident, options=None, persistent=False,
            bus=None):
        self.backend_domain = backend_domain
        self.ident = ident
        self.options = options or {}
        self.persistent = persistent
        self.bus = bus

    def __repr__(self):
        return "[%s]:%s" % (self.backend_domain, self.ident)

    def __hash__(self):
        # it's important to use the same hash as DeviceInfo
        return hash((self.backend_domain, self.ident))

    def __eq__(self, other):
        if not isinstance(self, other.__class__):
            return NotImplemented

        return self.backend_domain == other.backend_domain \
           and self.ident == other.ident

    def clone(self):
        '''Clone object instance'''
        return self.__class__(
            self.backend_domain,
            self.ident,
            self.options,
            self.persistent,
            self.bus,
        )

    @property
    def device(self):
        '''Get DeviceInfo object corresponding to this DeviceAssignment'''
        return self.backend_domain.devices[self.bus][self.ident]


class DeviceCollection:
    '''Bag for devices.

    Used as default value for :py:meth:`DeviceManager.__missing__` factory.

    :param vm: VM for which we manage devices
    :param bus: device bus

    This class emits following events on VM object:

        .. event:: device-attach:<class> (device, options)

            Fired when device is attached to a VM.

            Handler for this event can be asynchronous (a coroutine).

            :param device: :py:class:`DeviceInfo` object to be attached
            :param options: :py:class:`dict` of attachment options

        .. event:: device-pre-attach:<class> (device)

            Fired before device is attached to a VM

            Handler for this event can be asynchronous (a coroutine).

            :param device: :py:class:`DeviceInfo` object to be attached

        .. event:: device-detach:<class> (device)

            Fired when device is detached from a VM.

            Handler for this event can be asynchronous (a coroutine).

            :param device: :py:class:`DeviceInfo` object to be attached

        .. event:: device-pre-detach:<class> (device)

            Fired before device is detached from a VM

            Handler for this event can be asynchronous (a coroutine).

            :param device: :py:class:`DeviceInfo` object to be attached

        .. event:: device-list:<class>

            Fired to get list of devices exposed by a VM. Handlers of this
            event should return a list of py:class:`DeviceInfo` objects (or
            appropriate class specific descendant)

        .. event:: device-get:<class> (ident)

            Fired to get a single device, given by the `ident` parameter.
            Handlers of this event should either return appropriate object of
            :py:class:`DeviceInfo`, or :py:obj:`None`. Especially should not
            raise :py:class:`exceptions.KeyError`.

        .. event:: device-list-attached:<class> (persistent)

            Fired to get list of currently attached devices to a VM. Handlers
            of this event should return list of devices actually attached to
            a domain, regardless of its settings.

    '''

    def __init__(self, vm, bus):
        self._vm = vm
        self._bus = bus
        self._set = PersistentCollection()

        self.devclass = qubes.utils.get_entry_point_one(
            'qubes.devices', self._bus)

    @asyncio.coroutine
    def attach(self, device_assignment: DeviceAssignment):
        '''Attach (add) device to domain.

        :param DeviceInfo device: device object
        '''

        if device_assignment.bus is None:
            device_assignment.bus = self._bus
        elif device_assignment.bus != self._bus:
            raise ValueError(
                'Trying to attach DeviceAssignment of a different device class')

        if not device_assignment.persistent and self._vm.is_halted():
            raise qubes.exc.QubesVMNotRunningError(self._vm,
                "VM not running, can only attach device with persistent flag")
        device = device_assignment.device
        if device in self.assignments():
            raise DeviceAlreadyAttached(
                'device {!s} of class {} already attached to {!s}'.format(
                    device, self._bus, self._vm))
        yield from self._vm.fire_event_async('device-pre-attach:' + self._bus,
            pre_event=True,
            device=device, options=device_assignment.options)
        if device_assignment.persistent:
            self._set.add(device_assignment)
        yield from self._vm.fire_event_async('device-attach:' + self._bus,
            device=device, options=device_assignment.options)

    def load_persistent(self, device_assignment: DeviceAssignment):
        '''Load DeviceAssignment retrieved from qubes.xml

        This can be used only for loading qubes.xml, when VM events are not
        enabled yet.
        '''
        assert not self._vm.events_enabled
        assert device_assignment.persistent
        device_assignment.bus = self._bus
        self._set.add(device_assignment)

    def update_persistent(self, device: DeviceInfo, persistent: bool):
        '''Update `persistent` flag of already attached device.
        '''

        if self._vm.is_halted():
            raise qubes.exc.QubesVMNotStartedError(self._vm,
                'VM must be running to modify device persistence flag')
        assignments = [a for a in self.assignments() if a.device == device]
        if not assignments:
            raise qubes.exc.QubesValueError('Device not assigned')
        assert len(assignments) == 1
        assignment = assignments[0]

        # be careful to use already present assignment, not the provided one
        # - to not change options as a side effect
        if persistent and device not in self._set:
            assignment.persistent = True
            self._set.add(assignment)
        elif not persistent and device in self._set:
            self._set.discard(assignment)

    @asyncio.coroutine
    def detach(self, device_assignment: DeviceAssignment):
        '''Detach (remove) device from domain.

        :param DeviceInfo device: device object
        '''

        if device_assignment.bus is None:
            device_assignment.bus = self._bus
        else:
            assert device_assignment.bus == self._bus, \
                "Trying to attach DeviceAssignment of a different device class"

        if device_assignment in self._set and not self._vm.is_halted():
            raise qubes.exc.QubesVMNotHaltedError(self._vm,
                "Can not remove a persistent attachment from a non halted vm")
        if device_assignment not in self.assignments():
            raise DeviceNotAttached(
                'device {!s} of class {} not attached to {!s}'.format(
                    device_assignment.ident, self._bus, self._vm))

        device = device_assignment.device
        yield from self._vm.fire_event_async('device-pre-detach:' + self._bus,
            pre_event=True, device=device)
        if device in self._set:
            device_assignment.persistent = True
            self._set.discard(device_assignment)

        yield from self._vm.fire_event_async('device-detach:' + self._bus,
            device=device)

    def attached(self):
        '''List devices which are (or may be) attached to this vm '''
        attached = self._vm.fire_event('device-list-attached:' + self._bus,
            persistent=None)
        if attached:
            return [dev for dev, _ in attached]

        return []

    def persistent(self):
        ''' Devices persistently attached and safe to access before libvirt
            bootstrap.
        '''
        return [a.device for a in self._set]

    def assignments(self, persistent=None):
        '''List assignments for devices which are (or may be) attached to the
           vm.

        Devices may be attached persistently (so they are included in
        :file:`qubes.xml`) or not. Device can also be in :file:`qubes.xml`,
        but be temporarily detached.

        :param bool persistent: only include devices which are or are not
        attached persistently.
        '''

        try:
            devices = self._vm.fire_event('device-list-attached:' + self._bus,
                persistent=persistent)
        except Exception:  # pylint: disable=broad-except
            self._vm.log.exception('Failed to list {} devices'.format(
                self._bus))
            if persistent is True:
                # don't break app.save()
                return self._set
            raise
        result = set()
        for dev, options in devices:
            if dev in self._set and not persistent:
                continue
            if dev in self._set:
                result.add(self._set.get(dev))
            elif dev not in self._set and persistent:
                continue
            else:
                result.add(
                    DeviceAssignment(
                        backend_domain=dev.backend_domain,
                        ident=dev.ident, options=options,
                        bus=self._bus))
        if persistent is not False:
            result.update(self._set)
        return result

    def available(self):
        '''List devices exposed by this vm'''
        devices = self._vm.fire_event('device-list:' + self._bus)
        return devices

    def __iter__(self):
        return iter(self.available())

    def __getitem__(self, ident):
        '''Get device object with given ident.

        :returns: py:class:`DeviceInfo`

        If domain isn't running, it is impossible to check device validity,
        so return UnknownDevice object. Also do the same for non-existing
        devices - otherwise it will be impossible to detach already
        disconnected device.

        :raises AssertionError: when multiple devices with the same ident are
        found
        '''
        dev = self._vm.fire_event('device-get:' + self._bus, ident=ident)
        if dev:
            assert len(dev) == 1
            return dev[0]

        return UnknownDevice(self._vm, ident)


class DeviceManager(dict):
    '''Device manager that hold all devices by their classess.

    :param vm: VM for which we manage devices
    '''

    def __init__(self, vm):
        super().__init__()
        self._vm = vm

    def __missing__(self, key):
        self[key] = DeviceCollection(self._vm, key)
        return self[key]


class UnknownDevice(DeviceInfo):
    # pylint: disable=too-few-public-methods
    '''Unknown device - for example exposed by domain not running currently'''

    def __init__(self, backend_domain, ident, description=None,
            frontend_domain=None):
        if description is None:
            description = "Unknown device"
        super().__init__(backend_domain, ident, description,
            frontend_domain)


class PersistentCollection:

    ''' Helper object managing persistent `DeviceAssignment`s.
    '''

    def __init__(self):
        self._dict = {}

    def add(self, assignment: DeviceAssignment):
        ''' Add assignment to collection '''
        assert assignment.persistent
        vm = assignment.backend_domain
        ident = assignment.ident
        key = (vm, ident)
        assert key not in self._dict

        self._dict[key] = assignment

    def discard(self, assignment):
        ''' Discard assignment from collection '''
        assert assignment.persistent
        vm = assignment.backend_domain
        ident = assignment.ident
        key = (vm, ident)
        if key not in self._dict:
            raise KeyError
        del self._dict[key]

    def __contains__(self, device) -> bool:
        return (device.backend_domain, device.ident) in self._dict

    def get(self, device: DeviceInfo) -> DeviceAssignment:
        ''' Returns the corresponding `qubes.devices.DeviceAssignment` for the
            device. '''
        return self._dict[(device.backend_domain, device.ident)]

    def __iter__(self):
        return self._dict.values().__iter__()

    def __len__(self) -> int:
        return len(self._dict.keys())