#!/usr/bin/env python
#
# A library that provides a Python interface to the Telegram Bot API
# Copyright (C) 2015-2018
# Leandro Toledo de Souza <devs@python-telegram-bot.org>
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Lesser 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 Lesser Public License for more details.
#
# You should have received a copy of the GNU Lesser Public License
# along with this program.  If not, see [http://www.gnu.org/licenses/].
"""This module contains the Dispatcher class."""

import logging
import weakref
from functools import wraps
from threading import Thread, Lock, Event, current_thread, BoundedSemaphore
from time import sleep
from uuid import uuid4
from collections import defaultdict

from queue import Queue, Empty

from future.builtins import range

from telegram import TelegramError
from telegram.ext.handler import Handler
from telegram.utils.promise import Promise

logging.getLogger(__name__).addHandler(logging.NullHandler())
DEFAULT_GROUP = 0


def run_async(func):
    """Function decorator that will run the function in a new thread.

    Will run :attr:`telegram.ext.Dispatcher.run_async`.

    Using this decorator is only possible when only a single Dispatcher exist in the system.

    Note: Use this decorator to run handlers asynchronously.

    """
    @wraps(func)
    def async_func(*args, **kwargs):
        return Dispatcher.get_instance().run_async(func, *args, **kwargs)

    return async_func


class DispatcherHandlerStop(Exception):
    """Raise this in handler to prevent execution any other handler (even in different group)."""
    pass


class Dispatcher(object):
    """This class dispatches all kinds of updates to its registered handlers.

    Attributes:
        bot (:class:`telegram.Bot`): The bot object that should be passed to the handlers.
        update_queue (:obj:`Queue`): The synchronized queue that will contain the updates.
        job_queue (:class:`telegram.ext.JobQueue`): Optional. The :class:`telegram.ext.JobQueue`
            instance to pass onto handler callbacks.
        workers (:obj:`int`): Number of maximum concurrent worker threads for the ``@run_async``
            decorator.

    Args:
        bot (:class:`telegram.Bot`): The bot object that should be passed to the handlers.
        update_queue (:obj:`Queue`): The synchronized queue that will contain the updates.
        job_queue (:class:`telegram.ext.JobQueue`, optional): The :class:`telegram.ext.JobQueue`
                instance to pass onto handler callbacks.
        workers (:obj:`int`, optional): Number of maximum concurrent worker threads for the
            ``@run_async`` decorator. defaults to 4.

    """

    __singleton_lock = Lock()
    __singleton_semaphore = BoundedSemaphore()
    __singleton = None
    logger = logging.getLogger(__name__)

    def __init__(self, bot, update_queue, workers=4, exception_event=None, job_queue=None):
        self.bot = bot
        self.update_queue = update_queue
        self.job_queue = job_queue
        self.workers = workers

        self.user_data = defaultdict(dict)
        """:obj:`dict`: A dictionary handlers can use to store data for the user."""
        self.chat_data = defaultdict(dict)
        """:obj:`dict`: A dictionary handlers can use to store data for the chat."""
        self.handlers = {}
        """Dict[:obj:`int`, List[:class:`telegram.ext.Handler`]]: Holds the handlers per group."""
        self.groups = []
        """List[:obj:`int`]: A list with all groups."""
        self.error_handlers = []
        """List[:obj:`callable`]: A list of errorHandlers."""

        self.running = False
        """:obj:`bool`: Indicates if this dispatcher is running."""
        self.__stop_event = Event()
        self.__exception_event = exception_event or Event()
        self.__async_queue = Queue()
        self.__async_threads = set()

        # For backward compatibility, we allow a "singleton" mode for the dispatcher. When there's
        # only one instance of Dispatcher, it will be possible to use the `run_async` decorator.
        with self.__singleton_lock:
            if self.__singleton_semaphore.acquire(blocking=0):
                self._set_singleton(self)
            else:
                self._set_singleton(None)

    def _init_async_threads(self, base_name, workers):
        base_name = '{}_'.format(base_name) if base_name else ''

        for i in range(workers):
            thread = Thread(target=self._pooled, name='{}{}'.format(base_name, i))
            self.__async_threads.add(thread)
            thread.start()

    @classmethod
    def _set_singleton(cls, val):
        cls.logger.debug('Setting singleton dispatcher as %s', val)
        cls.__singleton = weakref.ref(val) if val else None

    @classmethod
    def get_instance(cls):
        """Get the singleton instance of this class.

        Returns:
            :class:`telegram.ext.Dispatcher`

        Raises:
            RuntimeError

        """
        if cls.__singleton is not None:
            return cls.__singleton()  # pylint: disable=not-callable
        else:
            raise RuntimeError('{} not initialized or multiple instances exist'.format(
                cls.__name__))

    def _pooled(self):
        thr_name = current_thread().getName()
        while 1:
            promise = self.__async_queue.get()

            # If unpacking fails, the thread pool is being closed from Updater._join_async_threads
            if not isinstance(promise, Promise):
                self.logger.debug("Closing run_async thread %s/%d", thr_name,
                                  len(self.__async_threads))
                break

            promise.run()
            if isinstance(promise.exception, DispatcherHandlerStop):
                self.logger.warning(
                    'DispatcherHandlerStop is not supported with async functions; func: %s',
                    promise.pooled_function.__name__)

    def run_async(self, func, *args, **kwargs):
        """Queue a function (with given args/kwargs) to be run asynchronously.

        Args:
            func (:obj:`callable`): The function to run in the thread.
            *args (:obj:`tuple`, optional): Arguments to `func`.
            **kwargs (:obj:`dict`, optional): Keyword arguments to `func`.

        Returns:
            Promise

        """
        # TODO: handle exception in async threads
        #       set a threading.Event to notify caller thread
        promise = Promise(func, args, kwargs)
        self.__async_queue.put(promise)
        return promise

    def start(self, ready=None):
        """Thread target of thread 'dispatcher'.

        Runs in background and processes the update queue.

        Args:
            ready (:obj:`threading.Event`, optional): If specified, the event will be set once the
                dispatcher is ready.

        """
        if self.running:
            self.logger.warning('already running')
            if ready is not None:
                ready.set()
            return

        if self.__exception_event.is_set():
            msg = 'reusing dispatcher after exception event is forbidden'
            self.logger.error(msg)
            raise TelegramError(msg)

        self._init_async_threads(uuid4(), self.workers)
        self.running = True
        self.logger.debug('Dispatcher started')

        if ready is not None:
            ready.set()

        while 1:
            try:
                # Pop update from update queue.
                update = self.update_queue.get(True, 1)
            except Empty:
                if self.__stop_event.is_set():
                    self.logger.debug('orderly stopping')
                    break
                elif self.__exception_event.is_set():
                    self.logger.critical('stopping due to exception in another thread')
                    break
                continue

            self.logger.debug('Processing Update: %s' % update)
            self.process_update(update)

        self.running = False
        self.logger.debug('Dispatcher thread stopped')

    def stop(self):
        """Stops the thread."""
        if self.running:
            self.__stop_event.set()
            while self.running:
                sleep(0.1)
            self.__stop_event.clear()

        # async threads must be join()ed only after the dispatcher thread was joined,
        # otherwise we can still have new async threads dispatched
        threads = list(self.__async_threads)
        total = len(threads)

        # Stop all threads in the thread pool by put()ting one non-tuple per thread
        for i in range(total):
            self.__async_queue.put(None)

        for i, thr in enumerate(threads):
            self.logger.debug('Waiting for async thread {0}/{1} to end'.format(i + 1, total))
            thr.join()
            self.__async_threads.remove(thr)
            self.logger.debug('async thread {0}/{1} has ended'.format(i + 1, total))

    @property
    def has_running_threads(self):
        return self.running or bool(self.__async_threads)

    def process_update(self, update):
        """Processes a single update.

        Args:
            update (:obj:`str` | :class:`telegram.Update` | :class:`telegram.TelegramError`):
                The update to process.

        """
        # An error happened while polling
        if isinstance(update, TelegramError):
            try:
                self.dispatch_error(None, update)
            except Exception:
                self.logger.exception('An uncaught error was raised while handling the error')
            return

        for group in self.groups:
            try:
                for handler in (x for x in self.handlers[group] if x.check_update(update)):
                    handler.handle_update(update, self)
                    break

            # Stop processing with any other handler.
            except DispatcherHandlerStop:
                self.logger.debug('Stopping further handlers due to DispatcherHandlerStop')
                break

            # Dispatch any error.
            except TelegramError as te:
                self.logger.warning('A TelegramError was raised while processing the Update')

                try:
                    self.dispatch_error(update, te)
                except DispatcherHandlerStop:
                    self.logger.debug('Error handler stopped further handlers')
                    break
                except Exception:
                    self.logger.exception('An uncaught error was raised while handling the error')

            # Errors should not stop the thread.
            except Exception:
                self.logger.exception('An uncaught error was raised while processing the update')

    def add_handler(self, handler, group=DEFAULT_GROUP):
        """Register a handler.

        TL;DR: Order and priority counts. 0 or 1 handlers per group will be used.

        A handler must be an instance of a subclass of :class:`telegram.ext.Handler`. All handlers
        are organized in groups with a numeric value. The default group is 0. All groups will be
        evaluated for handling an update, but only 0 or 1 handler per group will be used. If
        :class:`telegram.ext.DispatcherHandlerStop` is raised from one of the handlers, no further
        handlers (regardless of the group) will be called.

        The priority/order of handlers is determined as follows:

          * Priority of the group (lower group number == higher priority)
          * The first handler in a group which should handle an update (see
            :attr:`telegram.ext.Handler.check_update`) will be used. Other handlers from the
            group will not be used. The order in which handlers were added to the group defines the
            priority.

        Args:
            handler (:class:`telegram.ext.Handler`): A Handler instance.
            group (:obj:`int`, optional): The group identifier. Default is 0.

        """

        if not isinstance(handler, Handler):
            raise TypeError('handler is not an instance of {0}'.format(Handler.__name__))
        if not isinstance(group, int):
            raise TypeError('group is not int')

        if group not in self.handlers:
            self.handlers[group] = list()
            self.groups.append(group)
            self.groups = sorted(self.groups)

        self.handlers[group].append(handler)

    def remove_handler(self, handler, group=DEFAULT_GROUP):
        """Remove a handler from the specified group.

        Args:
            handler (:class:`telegram.ext.Handler`): A Handler instance.
            group (:obj:`object`, optional): The group identifier. Default is 0.

        """
        if handler in self.handlers[group]:
            self.handlers[group].remove(handler)
            if not self.handlers[group]:
                del self.handlers[group]
                self.groups.remove(group)

    def add_error_handler(self, callback):
        """Registers an error handler in the Dispatcher.

        Args:
            callback (:obj:`callable`): A function that takes ``Bot, Update, TelegramError`` as
                arguments.

        """
        self.error_handlers.append(callback)

    def remove_error_handler(self, callback):
        """Removes an error handler.

        Args:
            callback (:obj:`callable`): The error handler to remove.

        """
        if callback in self.error_handlers:
            self.error_handlers.remove(callback)

    def dispatch_error(self, update, error):
        """Dispatches an error.

        Args:
            update (:obj:`str` | :class:`telegram.Update` | None): The update that caused the error
            error (:class:`telegram.TelegramError`): The Telegram error that was raised.

        """
        if self.error_handlers:
            for callback in self.error_handlers:
                callback(self.bot, update, error)

        else:
            self.logger.exception(
                'No error handlers are registered, logging exception.', exc_info=error)
