import asyncio
import itertools
import random
import time

from .users import UserMethods
from .. import events, utils, errors
from ..tl import types, functions


class UpdateMethods(UserMethods):

    # region Public methods

    async def _run_until_disconnected(self):
        try:
            await self.disconnected
        except KeyboardInterrupt:
            self.disconnect()

    def run_until_disconnected(self):
        """
        Runs the event loop until `disconnect` is called or if an error
        while connecting/sending/receiving occurs in the background. In
        the latter case, said error will ``raise`` so you have a chance
        to ``except`` it on your own code.

        If the loop is already running, this method returns a coroutine
        that you should await on your own code.
        """
        if self.loop.is_running():
            return self._run_until_disconnected()
        try:
            return self.loop.run_until_complete(self.disconnected)
        except KeyboardInterrupt:
            self.disconnect()

    def on(self, event):
        """
        Decorator helper method around `add_event_handler`. Example:

        >>> from telethon import TelegramClient, events
        >>> client = TelegramClient(...)
        >>>
        >>> @client.on(events.NewMessage)
        ... async def handler(event):
        ...     ...
        ...
        >>>

        Args:
            event (`_EventBuilder` | `type`):
                The event builder class or instance to be used,
                for instance ``events.NewMessage``.
        """
        def decorator(f):
            self.add_event_handler(f, event)
            return f

        return decorator

    def add_event_handler(self, callback, event=None):
        """
        Registers the given callback to be called on the specified event.

        Args:
            callback (`callable`):
                The callable function accepting one parameter to be used.

                Note that if you have used `telethon.events.register` in
                the callback, ``event`` will be ignored, and instead the
                events you previously registered will be used.

            event (`_EventBuilder` | `type`, optional):
                The event builder class or instance to be used,
                for instance ``events.NewMessage``.

                If left unspecified, `telethon.events.raw.Raw` (the
                :tl:`Update` objects with no further processing) will
                be passed instead.
        """
        builders = events._get_handlers(callback)
        if builders is not None:
            for event in builders:
                self._event_builders.append((event, callback))
            return

        if isinstance(event, type):
            event = event()
        elif not event:
            event = events.Raw()

        self._event_builders.append((event, callback))

    def remove_event_handler(self, callback, event=None):
        """
        Inverse operation of :meth:`add_event_handler`.

        If no event is given, all events for this callback are removed.
        Returns how many callbacks were removed.
        """
        found = 0
        if event and not isinstance(event, type):
            event = type(event)

        i = len(self._event_builders)
        while i:
            i -= 1
            ev, cb = self._event_builders[i]
            if cb == callback and (not event or isinstance(ev, event)):
                del self._event_builders[i]
                found += 1

        return found

    def list_event_handlers(self):
        """
        Lists all added event handlers, returning a list of pairs
        consisting of (callback, event).
        """
        return [(callback, event) for event, callback in self._event_builders]

    async def catch_up(self):
        """
        "Catches up" on the missed updates while the client was offline.
        You should call this method after registering the event handlers
        so that the updates it loads can by processed by your script.

        This can also be used to forcibly fetch new updates if there are any.
        """
        state = self._state
        if state.pts == 0:
            # pts = 0 is invalid, pts = 1 will catch up since the beginning
            state.pts = 1

        self.session.catching_up = True
        try:
            while True:
                d = await self(functions.updates.GetDifferenceRequest(
                    state.pts, state.date, state.qts
                ))
                if isinstance(d, (types.updates.DifferenceSlice,
                                  types.updates.Difference)):
                    if isinstance(d, types.updates.Difference):
                        state = d.state
                    else:
                        state = d.intermediate_state

                    await self._handle_update(types.Updates(
                        users=d.users,
                        chats=d.chats,
                        date=state.date,
                        seq=state.seq,
                        updates=d.other_updates + [
                            types.UpdateNewMessage(m, 0, 0)
                            for m in d.new_messages
                        ]
                    ))
                else:
                    if isinstance(d, types.updates.DifferenceEmpty):
                        state.date = d.date
                        state.seq = d.seq
                    elif isinstance(d, types.updates.DifferenceTooLong):
                        state.pts = d.pts
                    break
        finally:
            self._state = state
            self.session.set_update_state(0, state)
            self.session.catching_up = False

    # endregion

    # region Private methods

    async def _handle_update(self, update):
        self.session.process_entities(update)
        if isinstance(update, (types.Updates, types.UpdatesCombined)):
            entities = {utils.get_peer_id(x): x for x in
                        itertools.chain(update.users, update.chats)}
            for u in update.updates:
                u._entities = entities
                await self._handle_update(u)
        elif isinstance(update, types.UpdateShort):
            await self._handle_update(update.update)
        else:
            update._entities = getattr(update, '_entities', {})
            if self._updates_queue is None:
                self._loop.create_task(self._dispatch_update(update))
            else:
                self._updates_queue.put_nowait(update)
                if not self._dispatching_updates_queue.is_set():
                    self._dispatching_updates_queue.set()
                    self._loop.create_task(self._dispatch_queue_updates())

        need_diff = False
        if hasattr(update, 'pts') and update.pts is not None:
            if self._state.pts and (update.pts - self._state.pts) > 1:
                need_diff = True
            self._state.pts = update.pts
        if hasattr(update, 'date'):
            self._state.date = update.date
        if hasattr(update, 'seq'):
            self._state.seq = update.seq

        # TODO make use of need_diff

    async def _update_loop(self):
        # Pings' ID don't really need to be secure, just "random"
        rnd = lambda: random.randrange(-2**63, 2**63)
        while self.is_connected():
            try:
                await asyncio.wait_for(
                    self.disconnected, timeout=60, loop=self._loop
                )
                continue  # We actually just want to act upon timeout
            except asyncio.TimeoutError:
                pass
            except asyncio.CancelledError:
                return
            except Exception as e:
                continue  # Any disconnected exception should be ignored

            # We also don't really care about their result.
            # Just send them periodically.
            self._sender.send(functions.PingRequest(rnd()))

            # Entities and cached files are not saved when they are
            # inserted because this is a rather expensive operation
            # (default's sqlite3 takes ~0.1s to commit changes). Do
            # it every minute instead. No-op if there's nothing new.
            self.session.save()

            # We need to send some content-related request at least hourly
            # for Telegram to keep delivering updates, otherwise they will
            # just stop even if we're connected. Do so every 30 minutes.
            #
            # TODO Call getDifference instead since it's more relevant
            if time.time() - self._last_request > 30 * 60:
                if not await self.is_user_authorized():
                    # What can be the user doing for so
                    # long without being logged in...?
                    continue

                await self(functions.updates.GetStateRequest())

    async def _dispatch_queue_updates(self):
        while not self._updates_queue.empty():
            await self._dispatch_update(self._updates_queue.get_nowait())

        self._dispatching_updates_queue.clear()

    async def _dispatch_update(self, update):
        built = EventBuilderDict(self, update)
        if self._conversations:
            for conv in self._conversations.values():
                if built[events.NewMessage]:
                    conv._on_new_message(built[events.NewMessage])
                if built[events.MessageEdited]:
                    conv._on_edit(built[events.MessageEdited])
                if built[events.MessageRead]:
                    conv._on_read(built[events.MessageRead])
                if conv._custom:
                    await conv._check_custom(built)

        for builder, callback in self._event_builders:
            event = built[type(builder)]
            if not event:
                continue

            if not builder.resolved:
                await builder.resolve(self)

            if not builder.filter(event):
                continue

            try:
                await callback(event)
            except errors.AlreadyInConversationError:
                name = getattr(callback, '__name__', repr(callback))
                self._log[__name__].debug(
                    'Event handler "%s" already has an open conversation, '
                    'ignoring new one', name)
            except events.StopPropagation:
                name = getattr(callback, '__name__', repr(callback))
                self._log[__name__].debug(
                    'Event handler "%s" stopped chain of propagation '
                    'for event %s.', name, type(event).__name__
                )
                break
            except Exception:
                name = getattr(callback, '__name__', repr(callback))
                self._log[__name__].exception('Unhandled exception on %s',
                                              name)

    async def _handle_auto_reconnect(self):
        # Upon reconnection, we want to send getState
        # for Telegram to keep sending us updates.
        try:
            self._log[__name__].info(
                'Asking for the current state after reconnect...')
            state = await self(functions.updates.GetStateRequest())
            self._log[__name__].info('Got new state! %s', state)
        except errors.RPCError as e:
            self._log[__name__].info('Failed to get current state: %r', e)

    # endregion


class EventBuilderDict:
    """
    Helper "dictionary" to return events from types and cache them.
    """
    def __init__(self, client, update):
        self.client = client
        self.update = update

    def __getitem__(self, builder):
        try:
            return self.__dict__[builder]
        except KeyError:
            event = self.__dict__[builder] = builder.build(self.update)
            if event:
                event.original_update = self.update
                if hasattr(event, '_set_client'):
                    event._set_client(self.client)
                else:
                    event._client = self.client

            return event