#
# Copyright (C) 2007-2010 Andrew Resch <andrewresch@gmail.com>
#
# This file is part of Deluge and is licensed under GNU General Public License 3.0, or later, with
# the additional special exception to link portions of this program with the OpenSSL library.
# See LICENSE for more details.
#

import logging
import traceback
from collections import defaultdict

from twisted.internet import reactor
from twisted.internet.defer import DeferredList, fail, maybeDeferred, succeed
from twisted.internet.task import LoopingCall, deferLater

log = logging.getLogger(__name__)


class ComponentAlreadyRegistered(Exception):
    pass


class ComponentException(Exception):
    def __init__(self, message, tb):
        super().__init__(message)
        self.message = message
        self.tb = tb

    def __str__(self):
        s = super().__str__()
        return '{}\n{}'.format(s, ''.join(self.tb))

    def __eq__(self, other):
        if isinstance(other, self.__class__):
            return self.message == other.message
        else:
            return False

    def __ne__(self, other):
        return not self.__eq__(other)


class Component:
    """Component objects are singletons managed by the :class:`ComponentRegistry`.

    When a new Component object is instantiated, it will be automatically
    registered with the :class:`ComponentRegistry`.

    The ComponentRegistry has the ability to start, stop, pause and shutdown the
    components registered with it.

    **Events:**

        **start()** - This method is called when the client has connected to a
                  Deluge core.

        **stop()** - This method is called when the client has disconnected from a
                 Deluge core.

        **update()** - This method is called every 1 second by default while the
                   Component is in a *Started* state.  The interval can be
                   specified during instantiation.  The update() timer can be
                   paused by instructing the :class:`ComponentRegistry` to pause
                   this Component.

       **pause()** - This method is called when the component is being paused.

       **resume()** - This method is called when the component resumes from a Paused
                    state.

        **shutdown()** - This method is called when the client is exiting.  If the
                     Component is in a "Started" state when this is called, a
                     call to stop() will be issued prior to shutdown().

    **States:**

        A Component can be in one of these 5 states.

        **Started** - The Component has been started by the :class:`ComponentRegistry`
                    and will have it's update timer started.

        **Starting** - The Component has had it's start method called, but it hasn't
                    fully started yet.

        **Stopped** - The Component has either been stopped or has yet to be started.

        **Stopping** - The Component has had its stop method called, but it hasn't
                    fully stopped yet.

        **Paused** - The Component has had its update timer stopped, but will
                    still be considered in a Started state.

    """

    def __init__(self, name, interval=1, depend=None):
        """Initialize component.

        Args:
            name (str): Name of component.
            interval (int, optional): The interval in seconds to call the update function.
            depend (list, optional): The names of components this component depends on.

        """
        self._component_name = name
        self._component_interval = interval
        self._component_depend = depend
        self._component_state = 'Stopped'
        self._component_timer = None
        self._component_starting_deferred = None
        self._component_stopping_deferred = None
        _ComponentRegistry.register(self)

    def __del__(self):
        if _ComponentRegistry:
            _ComponentRegistry.deregister(self)

    def _component_start_timer(self):
        self._component_timer = LoopingCall(self.update)
        self._component_timer.start(self._component_interval)

    def _component_start(self):
        def on_start(result):
            self._component_state = 'Started'
            self._component_starting_deferred = None
            self._component_start_timer()
            return True

        def on_start_fail(result):
            self._component_state = 'Stopped'
            self._component_starting_deferred = None
            log.error(result)
            return fail(result)

        if self._component_state == 'Stopped':
            self._component_state = 'Starting'
            d = deferLater(reactor, 0, self.start)
            d.addCallbacks(on_start, on_start_fail)
            self._component_starting_deferred = d
        elif self._component_state == 'Starting':
            return self._component_starting_deferred
        elif self._component_state == 'Started':
            d = succeed(True)
        else:
            d = fail(
                ComponentException(
                    'Trying to start component "%s" but it is '
                    'not in a stopped state. Current state: %s'
                    % (self._component_name, self._component_state),
                    traceback.format_stack(limit=4),
                )
            )
        return d

    def _component_stop(self):
        def on_stop(result):
            self._component_state = 'Stopped'
            if self._component_timer and self._component_timer.running:
                self._component_timer.stop()
            return True

        def on_stop_fail(result):
            self._component_state = 'Started'
            self._component_stopping_deferred = None
            log.error(result)
            return result

        if self._component_state != 'Stopped' and self._component_state != 'Stopping':
            self._component_state = 'Stopping'
            d = maybeDeferred(self.stop)
            d.addCallback(on_stop)
            d.addErrback(on_stop_fail)
            self._component_stopping_deferred = d

        if self._component_state == 'Stopping':
            return self._component_stopping_deferred

        return succeed(None)

    def _component_pause(self):
        def on_pause(result):
            self._component_state = 'Paused'
            if self._component_timer and self._component_timer.running:
                self._component_timer.stop()

        if self._component_state == 'Started':
            d = maybeDeferred(self.pause)
            d.addCallback(on_pause)
        elif self._component_state == 'Paused':
            d = succeed(None)
        else:
            d = fail(
                ComponentException(
                    'Trying to pause component "%s" but it is '
                    'not in a started state. Current state: %s'
                    % (self._component_name, self._component_state),
                    traceback.format_stack(limit=4),
                )
            )
        return d

    def _component_resume(self):
        def on_resume(result):
            self._component_state = 'Started'
            self._component_start_timer()

        if self._component_state == 'Paused':
            d = maybeDeferred(self.resume)
            d.addCallback(on_resume)
        else:
            d = fail(
                ComponentException(
                    'Trying to resume component "%s" but it is '
                    'not in a paused state. Current state: %s'
                    % (self._component_name, self._component_state),
                    traceback.format_stack(limit=4),
                )
            )
        return d

    def _component_shutdown(self):
        def on_stop(result):
            return maybeDeferred(self.shutdown)

        d = self._component_stop()
        d.addCallback(on_stop)
        return d

    def get_state(self):
        return self._component_state

    def start(self):
        pass

    def stop(self):
        pass

    def update(self):
        pass

    def shutdown(self):
        pass

    def pause(self):
        pass

    def resume(self):
        pass


class ComponentRegistry:
    """The ComponentRegistry holds a list of currently registered :class:`Component` objects.

    It is used to manage the Components by starting, stopping, pausing and shutting them down.
    """

    def __init__(self):
        self.components = {}
        # Stores all of the components that are dependent on a particular component
        self.dependents = defaultdict(list)

    def register(self, obj):
        """Register a component object with the registry.

        Note:
            This is done automatically when a Component object is instantiated.

        Args:
            obj (Component): A component object to register.

        Raises:
            ComponentAlreadyRegistered: If a component with the same name is already registered.

        """
        name = obj._component_name
        if name in self.components:
            raise ComponentAlreadyRegistered(
                'Component already registered with name %s' % name
            )

        self.components[obj._component_name] = obj
        if obj._component_depend:
            for depend in obj._component_depend:
                self.dependents[depend].append(name)

    def deregister(self, obj):
        """Deregister a component from the registry.  A stop will be
        issued to the component prior to deregistering it.

        Args:
            obj (Component): a component object to deregister

        Returns:
            Deferred: a deferred object that will fire once the Component has been
                successfully deregistered

        """
        if obj in self.components.values():
            log.debug('Deregistering Component: %s', obj._component_name)
            d = self.stop([obj._component_name])

            def on_stop(result, name):
                # Component may have been removed, so pop to ensure it doesn't fail
                self.components.pop(name, None)

            return d.addCallback(on_stop, obj._component_name)
        else:
            return succeed(None)

    def start(self, names=None):
        """Start Components, and their dependencies, that are currently in a Stopped state.

        Note:
            If no names are specified then all registered components will be started.

        Args:
            names (list): A list of Components to start and their dependencies.

        Returns:
            Deferred: Fired once all Components have been successfully started.

        """
        # Start all the components if names is empty
        if not names:
            names = list(self.components)
        elif isinstance(names, str):
            names = [names]

        def on_depends_started(result, name):
            return self.components[name]._component_start()

        deferreds = []

        for name in names:
            if self.components[name]._component_depend:
                # This component has depends, so we need to start them first.
                d = self.start(self.components[name]._component_depend)
                d.addCallback(on_depends_started, name)
                deferreds.append(d)
            else:
                deferreds.append(self.components[name]._component_start())

        return DeferredList(deferreds)

    def stop(self, names=None):
        """Stop Components that are currently not in a Stopped state.

        Note:
            If no names are specified then all registered components will be stopped.

        Args:
            names (list): A list of Components to stop.

        Returns:
            Deferred: Fired once all Components have been successfully stopped.

        """
        if not names:
            names = list(self.components)
        elif isinstance(names, str):
            names = [names]

        def on_dependents_stopped(result, name):
            return self.components[name]._component_stop()

        stopped_in_deferred = set()
        deferreds = []

        for name in names:
            if name in stopped_in_deferred:
                continue
            if name in self.components:
                if name in self.dependents:
                    # If other components depend on this component, stop them first
                    d = self.stop(self.dependents[name]).addCallback(
                        on_dependents_stopped, name
                    )
                    deferreds.append(d)
                    stopped_in_deferred.update(self.dependents[name])
                else:
                    deferreds.append(self.components[name]._component_stop())

        return DeferredList(deferreds)

    def pause(self, names=None):
        """Pause Components that are currently in a Started state.

        Note:
            If no names are specified then all registered components will be paused.

        Args:
            names (list): A list of Components to pause.

        Returns:
            Deferred: Fired once all Components have been successfully paused.

        """
        if not names:
            names = list(self.components)
        elif isinstance(names, str):
            names = [names]

        deferreds = []

        for name in names:
            if self.components[name]._component_state == 'Started':
                deferreds.append(self.components[name]._component_pause())

        return DeferredList(deferreds)

    def resume(self, names=None):
        """Resume Components that are currently in a Paused state.

        Note:
            If no names are specified then all registered components will be resumed.

        Args:
            names (list): A list of Components to to resume.

        Returns:
            Deferred: Fired once all Components have been successfully resumed.

        """
        if not names:
            names = list(self.components)
        elif isinstance(names, str):
            names = [names]

        deferreds = []

        for name in names:
            if self.components[name]._component_state == 'Paused':
                deferreds.append(self.components[name]._component_resume())

        return DeferredList(deferreds)

    def shutdown(self):
        """Shutdown all Components regardless of state.

        This will call stop() on all the components prior to shutting down. This should be called
        when the program is exiting to ensure all Components have a chance to properly shutdown.

        Returns:
            Deferred: Fired once all Components have been successfully shut down.

        """

        def on_stopped(result):
            return DeferredList(
                [comp._component_shutdown() for comp in list(self.components.values())]
            )

        return self.stop(list(self.components)).addCallback(on_stopped)

    def update(self):
        """Update all Components that are in a Started state."""
        for component in self.components.items():
            try:
                component.update()
            except BaseException as ex:
                log.exception(ex)


_ComponentRegistry = ComponentRegistry()

deregister = _ComponentRegistry.deregister
start = _ComponentRegistry.start
stop = _ComponentRegistry.stop
pause = _ComponentRegistry.pause
resume = _ComponentRegistry.resume
update = _ComponentRegistry.update
shutdown = _ComponentRegistry.shutdown


def get(name):
    """Return a reference to a component.

    Args:
        name (str): The Component name to get.

    Returns:
        Component: The Component object.

    Raises:
        KeyError: If the Component does not exist.

    """
    return _ComponentRegistry.components[name]
