# -*- coding: utf-8 -*-
"""Event loop implementation."""
from __future__ import absolute_import, unicode_literals

import errno
import itertools
from contextlib import contextmanager
from time import sleep
from types import GeneratorType as generator  # noqa

from kombu.five import Empty, python_2_unicode_compatible, range
from kombu.log import get_logger
from kombu.utils.compat import fileno
from kombu.utils.eventio import ERR, READ, WRITE, poll
from kombu.utils.objects import cached_property
from vine import Thenable, promise

from .timer import Timer

__all__ = ['Hub', 'get_event_loop', 'set_event_loop']
logger = get_logger(__name__)

_current_loop = None

W_UNKNOWN_EVENT = """\
Received unknown event %r for fd %r, please contact support!\
"""


class Stop(BaseException):
    """Stops the event loop."""


def _raise_stop_error():
    raise Stop()


@contextmanager
def _dummy_context(*args, **kwargs):
    yield


def get_event_loop():
    """Get current event loop object."""
    return _current_loop


def set_event_loop(loop):
    """Set the current event loop object."""
    global _current_loop
    _current_loop = loop
    return loop


@python_2_unicode_compatible
class Hub(object):
    """Event loop object.

    Arguments:
        timer (kombu.async.Timer): Specify custom timer instance.
    """

    #: Flag set if reading from an fd will not block.
    READ = READ

    #: Flag set if writing to an fd will not block.
    WRITE = WRITE

    #: Flag set on error, and the fd should be read from asap.
    ERR = ERR

    #: List of callbacks to be called when the loop is exiting,
    #: applied with the hub instance as sole argument.
    on_close = None

    def __init__(self, timer=None):
        self.timer = timer if timer is not None else Timer()

        self.readers = {}
        self.writers = {}
        self.on_tick = set()
        self.on_close = set()
        self._ready = set()

        self._running = False
        self._loop = None

        # The eventloop (in celery.worker.loops)
        # will merge fds in this set and then instead of calling
        # the callback for each ready fd it will call the
        # :attr:`consolidate_callback` with the list of ready_fds
        # as an argument.  This API is internal and is only
        # used by the multiprocessing pool to find inqueues
        # that are ready to write.
        self.consolidate = set()
        self.consolidate_callback = None

        self.propagate_errors = ()

        self._create_poller()

    def reset(self):
        self.close()
        self._create_poller()

    def _create_poller(self):
        self.poller = poll()
        self._register_fd = self.poller.register
        self._unregister_fd = self.poller.unregister

    def _close_poller(self):
        if self.poller is not None:
            self.poller.close()
            self.poller = None
            self._register_fd = None
            self._unregister_fd = None

    def stop(self):
        self.call_soon(_raise_stop_error)

    def __repr__(self):
        return '<Hub@{0:#x}: R:{1} W:{2}>'.format(
            id(self), len(self.readers), len(self.writers),
        )

    def fire_timers(self, min_delay=1, max_delay=10, max_timers=10,
                    propagate=()):
        timer = self.timer
        delay = None
        if timer and timer._queue:
            for i in range(max_timers):
                delay, entry = next(self.scheduler)
                if entry is None:
                    break
                try:
                    entry()
                except propagate:
                    raise
                except (MemoryError, AssertionError):
                    raise
                except OSError as exc:
                    if exc.errno == errno.ENOMEM:
                        raise
                    logger.error('Error in timer: %r', exc, exc_info=1)
                except Exception as exc:
                    logger.error('Error in timer: %r', exc, exc_info=1)
        return min(delay or min_delay, max_delay)

    def _remove_from_loop(self, fd):
        try:
            self._unregister(fd)
        finally:
            self._discard(fd)

    def add(self, fd, callback, flags, args=(), consolidate=False):
        fd = fileno(fd)
        try:
            self.poller.register(fd, flags)
        except ValueError:
            self._remove_from_loop(fd)
            raise
        else:
            dest = self.readers if flags & READ else self.writers
            if consolidate:
                self.consolidate.add(fd)
                dest[fd] = None
            else:
                dest[fd] = callback, args

    def remove(self, fd):
        fd = fileno(fd)
        self._remove_from_loop(fd)

    def run_forever(self):
        self._running = True
        try:
            while 1:
                try:
                    self.run_once()
                except Stop:
                    break
        finally:
            self._running = False

    def run_once(self):
        try:
            next(self.loop)
        except StopIteration:
            self._loop = None

    def call_soon(self, callback, *args):
        if not isinstance(callback, Thenable):
            callback = promise(callback, args)
        self._ready.add(callback)
        return callback

    def call_later(self, delay, callback, *args):
        return self.timer.call_after(delay, callback, args)

    def call_at(self, when, callback, *args):
        return self.timer.call_at(when, callback, args)

    def call_repeatedly(self, delay, callback, *args):
        return self.timer.call_repeatedly(delay, callback, args)

    def add_reader(self, fds, callback, *args):
        return self.add(fds, callback, READ | ERR, args)

    def add_writer(self, fds, callback, *args):
        return self.add(fds, callback, WRITE, args)

    def remove_reader(self, fd):
        writable = fd in self.writers
        on_write = self.writers.get(fd)
        try:
            self._remove_from_loop(fd)
        finally:
            if writable:
                cb, args = on_write
                self.add(fd, cb, WRITE, args)

    def remove_writer(self, fd):
        readable = fd in self.readers
        on_read = self.readers.get(fd)
        try:
            self._remove_from_loop(fd)
        finally:
            if readable:
                cb, args = on_read
                self.add(fd, cb, READ | ERR, args)

    def _unregister(self, fd):
        try:
            self.poller.unregister(fd)
        except (AttributeError, KeyError, OSError):
            pass

    def close(self, *args):
        [self._unregister(fd) for fd in self.readers]
        self.readers.clear()
        [self._unregister(fd) for fd in self.writers]
        self.writers.clear()
        self.consolidate.clear()
        self._close_poller()
        for callback in self.on_close:
            callback(self)

    def _discard(self, fd):
        fd = fileno(fd)
        self.readers.pop(fd, None)
        self.writers.pop(fd, None)
        self.consolidate.discard(fd)

    def on_callback_error(self, callback, exc):
        logger.error(
            'Callback %r raised exception: %r', callback, exc, exc_info=1,
        )

    def create_loop(self,
                    generator=generator, sleep=sleep, min=min, next=next,
                    Empty=Empty, StopIteration=StopIteration,
                    KeyError=KeyError, READ=READ, WRITE=WRITE, ERR=ERR):
        readers, writers = self.readers, self.writers
        poll = self.poller.poll
        fire_timers = self.fire_timers
        hub_remove = self.remove
        scheduled = self.timer._queue
        consolidate = self.consolidate
        consolidate_callback = self.consolidate_callback
        on_tick = self.on_tick
        propagate = self.propagate_errors
        todo = self._ready

        while 1:
            for tick_callback in on_tick:
                tick_callback()

            # To avoid infinite loop where one of the callables adds items
            # to self._ready (via call_soon or otherwise), we take pop only
            # N items from the ready set.
            # N represents the current number of items on the set.
            # That way if a todo adds another one to the ready set,
            # we will break early and allow execution of readers and writers.
            current_todos = len(todo)
            for _ in itertools.repeat(None, current_todos):
                if not todo:
                    break

                item = todo.pop()
                if item:
                    item()

            poll_timeout = fire_timers(propagate=propagate) if scheduled else 1
            #  print('[[[HUB]]]: %s' % (self.repr_active(),))
            if readers or writers:
                to_consolidate = []
                try:
                    events = poll(poll_timeout)
                    #  print('[EVENTS]: %s' % (self.repr_events(events),))
                except ValueError:  # Issue 882
                    raise StopIteration()

                for fd, event in events or ():
                    general_error = False
                    if fd in consolidate and \
                            writers.get(fd) is None:
                        to_consolidate.append(fd)
                        continue
                    cb = cbargs = None

                    if event & READ:
                        try:
                            cb, cbargs = readers[fd]
                        except KeyError:
                            self.remove_reader(fd)
                            continue
                    elif event & WRITE:
                        try:
                            cb, cbargs = writers[fd]
                        except KeyError:
                            self.remove_writer(fd)
                            continue
                    elif event & ERR:
                        general_error = True
                    else:
                        logger.info(W_UNKNOWN_EVENT, event, fd)
                        general_error = True

                    if general_error:
                        try:
                            cb, cbargs = (readers.get(fd) or
                                          writers.get(fd))
                        except TypeError:
                            pass

                    if cb is None:
                        self.remove(fd)
                        continue

                    if isinstance(cb, generator):
                        try:
                            next(cb)
                        except OSError as exc:
                            if exc.errno != errno.EBADF:
                                raise
                            hub_remove(fd)
                        except StopIteration:
                            pass
                        except Exception:
                            hub_remove(fd)
                            raise
                    else:
                        try:
                            cb(*cbargs)
                        except Empty:
                            pass
                if to_consolidate:
                    consolidate_callback(to_consolidate)
            else:
                # no sockets yet, startup is probably not done.
                sleep(min(poll_timeout, 0.1))
            yield

    def repr_active(self):
        from .debug import repr_active
        return repr_active(self)

    def repr_events(self, events):
        from .debug import repr_events
        return repr_events(self, events or [])

    @cached_property
    def scheduler(self):
        return iter(self.timer)

    @property
    def loop(self):
        if self._loop is None:
            self._loop = self.create_loop()
        return self._loop