# -*- coding: utf-8 -*-

from pyee._base import EventEmitter

from twisted.internet.defer import Deferred, ensureDeferred
from twisted.python.failure import Failure

try:
    from asyncio import iscoroutine
except ImportError:
    iscoroutine = None


__all__ = ['TwistedEventEmitter']


class TwistedEventEmitter(EventEmitter):
    """An event emitter class which can run twisted coroutines and handle
    returned Deferreds, in addition to synchronous blocking functions. For
    example::

        @ee.on('event')
        @inlineCallbacks
        def async_handler(*args, **kwargs):
            yield returns_a_deferred()

    or::

        @ee.on('event')
        async def async_handler(*args, **kwargs):
            await returns_a_deferred()


    When async handlers fail, Failures are first emitted on the ``failure``
    event. If there are no ``failure`` handlers, the Failure's associated
    exception is then emitted on the ``error`` event. If there are no ``error``
    handlers, the exception is raised. For consistency, when handlers raise
    errors synchronously, they're captured, wrapped in a Failure and treated
    as an async failure. This is unlike the behavior of BaseEventEmitter,
    which have no special error handling.

    For twisted coroutine event handlers, calling emit is non-blocking.
    In other words, you do not have to await any results from emit, and the
    coroutine is scheduled in a fire-and-forget fashion.

    Similar behavior occurs for "sync" functions which return Deferreds.
    """
    def __init__(self):
        super(TwistedEventEmitter, self).__init__()

    def _emit_run(self, f, args, kwargs):
        try:
            result = f(*args, **kwargs)
        except Exception:
            self.emit('failure', Failure())
        else:
            if iscoroutine and iscoroutine(result):
                d = ensureDeferred(result)
            elif isinstance(result, Deferred):
                d = result
            else:
                d = None
            if d:
                @d.addErrback
                def _errback(failure):
                    if failure:
                        self.emit('failure', failure)

    def _emit_handle_potential_error(self, event, error):
        if event == 'failure':
            self.emit('error', error.value)
        else:
            (
                super(TwistedEventEmitter, self)
            )._emit_handle_potential_error(event, error)
