import collections
import time
import traceback

from eventlet import api


class Cancelled(RuntimeError):
    pass


class NOT_USED:
    def __repr__(self):
        return 'NOT_USED'

NOT_USED = NOT_USED()

class event(object):
    """An abstraction where an arbitrary number of coroutines
    can wait for one event from another.

    Events differ from channels in two ways:

    1. calling :meth:`send` does not unschedule the current coroutine
    2. :meth:`send` can only be called once; use :meth:`reset` to prepare the
       event for another :meth:`send`
    
    They are ideal for communicating return values between coroutines.

    >>> from eventlet import coros, api
    >>> evt = coros.event()
    >>> def baz(b):
    ...     evt.send(b + 1)
    ...
    >>> _ = api.spawn(baz, 3)
    >>> evt.wait()
    4
    """
    _result = None
    def __init__(self):
        self._waiters = set()
        self.reset()

    def __str__(self):
        params = (self.__class__.__name__, hex(id(self)), self._result, self._exc, len(self._waiters))
        return '<%s at %s result=%r _exc=%r _waiters[%d]>' % params

    def reset(self):
        """ Reset this event so it can be used to send again.
        Can only be called after :meth:`send` has been called.

        >>> from eventlet import coros
        >>> evt = coros.event()
        >>> evt.send(1)
        >>> evt.reset()
        >>> evt.send(2)
        >>> evt.wait()
        2

        Calling reset multiple times in a row is an error.

        >>> evt.reset()
        >>> evt.reset()
        Traceback (most recent call last):
        ...
        AssertionError: Trying to re-reset() a fresh event.

        """
        assert self._result is not NOT_USED, 'Trying to re-reset() a fresh event.'
        self.epoch = time.time()
        self._result = NOT_USED
        self._exc = None

    def ready(self):
        """ Return true if the :meth:`wait` call will return immediately.
        Used to avoid waiting for things that might take a while to time out.
        For example, you can put a bunch of events into a list, and then visit
        them all repeatedly, calling :meth:`ready` until one returns ``True``,
        and then you can :meth:`wait` on that one."""
        return self._result is not NOT_USED

    def has_exception(self):
        return self._exc is not None

    def has_result(self):
        return self._result is not NOT_USED and self._exc is None

    def poll(self, notready=None):
        if self.ready():
            return self.wait()
        return notready

    # QQQ make it return tuple (type, value, tb) instead of raising
    # because
    # 1) "poll" does not imply raising
    # 2) it's better not to screw up caller's sys.exc_info() by default
    #    (e.g. if caller wants to calls the function in except or finally)
    def poll_exception(self, notready=None):
        if self.has_exception():
            return self.wait()
        return notready

    def poll_result(self, notready=None):
        if self.has_result():
            return self.wait()
        return notready

    def wait(self):
        """Wait until another coroutine calls :meth:`send`.
        Returns the value the other coroutine passed to
        :meth:`send`.

        >>> from eventlet import coros, api
        >>> evt = coros.event()
        >>> def wait_on():
        ...    retval = evt.wait()
        ...    print "waited for", retval
        >>> _ = api.spawn(wait_on)
        >>> evt.send('result')
        >>> api.sleep(0)
        waited for result

        Returns immediately if the event has already
        occured.

        >>> evt.wait()
        'result'
        """
        if self._result is NOT_USED:
            self._waiters.add(api.getcurrent())
            try:
                return api.get_hub().switch()
            finally:
                self._waiters.discard(api.getcurrent())
        if self._exc is not None:
            api.getcurrent().throw(*self._exc)
        return self._result

    def send(self, result=None, exc=None):
        """Makes arrangements for the waiters to be woken with the
        result and then returns immediately to the parent.

        >>> from eventlet import coros, api
        >>> evt = coros.event()
        >>> def waiter():
        ...     print 'about to wait'
        ...     result = evt.wait()
        ...     print 'waited for', result
        >>> _ = api.spawn(waiter)
        >>> api.sleep(0)
        about to wait
        >>> evt.send('a')
        >>> api.sleep(0)
        waited for a

        It is an error to call :meth:`send` multiple times on the same event.

        >>> evt.send('whoops')
        Traceback (most recent call last):
        ...
        AssertionError: Trying to re-send() an already-triggered event.

        Use :meth:`reset` between :meth:`send` s to reuse an event object.
        """
        assert self._result is NOT_USED, 'Trying to re-send() an already-triggered event.'
        self._result = result
        if exc is not None and not isinstance(exc, tuple):
            exc = (exc, )
        self._exc = exc
        hub = api.get_hub()
        if self._waiters:
            hub.schedule_call_global(0, self._do_send, self._result, self._exc, self._waiters.copy())

    def _do_send(self, result, exc, waiters):
        while waiters:
            waiter = waiters.pop()
            if waiter in self._waiters:
                if exc is None:
                    waiter.switch(result)
                else:
                    waiter.throw(*exc)

    def send_exception(self, *args):
        # the arguments and the same as for greenlet.throw
        return self.send(None, args)


class Semaphore(object):
    """An unbounded semaphore.
    Optionally initialize with a resource *count*, then :meth:`acquire` and
    :meth:`release` resources as needed. Attempting to :meth:`acquire` when
    *count* is zero suspends the calling coroutine until *count* becomes
    nonzero again.
    """

    def __init__(self, count=0):
        self.counter  = count
        self._waiters = set()

    def __repr__(self):
        params = (self.__class__.__name__, hex(id(self)), self.counter, len(self._waiters))
        return '<%s at %s c=%s _w[%s]>' % params

    def __str__(self):
        params = (self.__class__.__name__, self.counter, len(self._waiters))
        return '<%s c=%s _w[%s]>' % params

    def locked(self):
        return self.counter <= 0

    def bounded(self):
        # for consistency with BoundedSemaphore
        return False

    def acquire(self, blocking=True):
        if not blocking and self.locked():
            return False
        if self.counter <= 0:
            self._waiters.add(api.getcurrent())
            try:
                while self.counter <= 0:
                    api.get_hub().switch()
            finally:
                self._waiters.discard(api.getcurrent())
        self.counter -= 1
        return True

    def __enter__(self):
        self.acquire()

    def release(self, blocking=True):
        # `blocking' parameter is for consistency with BoundedSemaphore and is ignored
        self.counter += 1
        if self._waiters:
            api.get_hub().schedule_call_global(0, self._do_acquire)
        return True

    def _do_acquire(self):
        if self._waiters and self.counter>0:
            waiter = self._waiters.pop()
            waiter.switch()

    def __exit__(self, typ, val, tb):
        self.release()

    @property
    def balance(self):
        # positive means there are free items
        # zero means there are no free items but nobody has requested one
        # negative means there are requests for items, but no items
        return self.counter - len(self._waiters)


class BoundedSemaphore(object):
    """A bounded semaphore.
    Optionally initialize with a resource *count*, then :meth:`acquire` and
    :meth:`release` resources as needed. Attempting to :meth:`acquire` when
    *count* is zero suspends the calling coroutine until count becomes nonzero
    again.  Attempting to :meth:`release` after *count* has reached *limit*
    suspends the calling coroutine until *count* becomes less than *limit*
    again.
    """
    def __init__(self, count, limit):
        if count > limit:
            # accidentally, this also catches the case when limit is None
            raise ValueError("'count' cannot be more than 'limit'")
        self.lower_bound = Semaphore(count)
        self.upper_bound = Semaphore(limit-count)

    def __repr__(self):
        params = (self.__class__.__name__, hex(id(self)), self.balance, self.lower_bound, self.upper_bound)
        return '<%s at %s b=%s l=%s u=%s>' % params

    def __str__(self):
        params = (self.__class__.__name__, self.balance, self.lower_bound, self.upper_bound)
        return '<%s b=%s l=%s u=%s>' % params

    def locked(self):
        return self.lower_bound.locked()

    def bounded(self):
        return self.upper_bound.locked()

    def acquire(self, blocking=True):
        if not blocking and self.locked():
            return False
        self.upper_bound.release()
        try:
            return self.lower_bound.acquire()
        except:
            self.upper_bound.counter -= 1
            # using counter directly means that it can be less than zero.
            # however I certainly don't need to wait here and I don't seem to have
            # a need to care about such inconsistency
            raise

    def __enter__(self):
        self.acquire()

    def release(self, blocking=True):
        if not blocking and self.bounded():
            return False
        self.lower_bound.release()
        try:
            return self.upper_bound.acquire()
        except:
            self.lower_bound.counter -= 1
            raise

    def __exit__(self, typ, val, tb):
        self.release()

    @property
    def balance(self):
        return self.lower_bound.balance - self.upper_bound.balance


def semaphore(count=0, limit=None):
    if limit is None:
        return Semaphore(count)
    else:
        return BoundedSemaphore(count, limit)


class metaphore(object):
    """This is sort of an inverse semaphore: a counter that starts at 0 and
    waits only if nonzero. It's used to implement a "wait for all" scenario.

    >>> from eventlet import api, coros
    >>> count = coros.metaphore()
    >>> count.wait()
    >>> def decrementer(count, id):
    ...     print "%s decrementing" % id
    ...     count.dec()
    ...
    >>> _ = api.spawn(decrementer, count, 'A')
    >>> _ = api.spawn(decrementer, count, 'B')
    >>> count.inc(2)
    >>> count.wait()
    A decrementing
    B decrementing
    """
    def __init__(self):
        self.counter = 0
        self.event   = event()
        # send() right away, else we'd wait on the default 0 count!
        self.event.send()

    def inc(self, by=1):
        """Increment our counter. If this transitions the counter from zero to
        nonzero, make any subsequent :meth:`wait` call wait.
        """
        assert by > 0
        self.counter += by
        if self.counter == by:
            # If we just incremented self.counter by 'by', and the new count
            # equals 'by', then the old value of self.counter was 0.
            # Transitioning from 0 to a nonzero value means wait() must
            # actually wait.
            self.event.reset()

    def dec(self, by=1):
        """Decrement our counter. If this transitions the counter from nonzero
        to zero, a current or subsequent wait() call need no longer wait.
        """
        assert by > 0
        self.counter -= by
        if self.counter <= 0:
            # Don't leave self.counter < 0, that will screw things up in
            # future calls.
            self.counter = 0
            # Transitioning from nonzero to 0 means wait() need no longer wait.
            self.event.send()

    def wait(self):
        """Suspend the caller only if our count is nonzero. In that case,
        resume the caller once the count decrements to zero again.
        """
        self.event.wait()

def execute(func, *args, **kw):
    """ Executes an operation asynchronously in a new coroutine, returning
    an event to retrieve the return value.

    This has the same api as the :meth:`eventlet.coros.CoroutinePool.execute`
    method; the only difference is that this one creates a new coroutine
    instead of drawing from a pool.

    >>> from eventlet import coros
    >>> evt = coros.execute(lambda a: ('foo', a), 1)
    >>> evt.wait()
    ('foo', 1)
    """
    evt = event()
    def _really_execute():
        evt.send(func(*args, **kw))
    api.spawn(_really_execute)
    return evt


def CoroutinePool(*args, **kwargs):
    from eventlet.pool import Pool
    return Pool(*args, **kwargs)


class Queue(object):

    def __init__(self):
        self.items = collections.deque()
        self._waiters = set()

    def __nonzero__(self):
        return len(self.items)>0

    def __len__(self):
        return len(self.items)

    def __repr__(self):
        params = (self.__class__.__name__, hex(id(self)), len(self.items), len(self._waiters))
        return '<%s at %s items[%d] _waiters[%s]>' % params

    def send(self, result=None, exc=None):
        if exc is not None and not isinstance(exc, tuple):
            exc = (exc, )
        self.items.append((result, exc))
        if self._waiters:
            api.get_hub().schedule_call_global(0, self._do_send)

    def send_exception(self, *args):
        # the arguments are the same as for greenlet.throw
        return self.send(exc=args)

    def _do_send(self):
        if self._waiters and self.items:
            waiter = self._waiters.pop()
            result, exc = self.items.popleft()
            waiter.switch((result, exc))

    def wait(self):
        if self.items:
            result, exc = self.items.popleft()
            if exc is None:
                return result
            else:
                api.getcurrent().throw(*exc)
        else:
            self._waiters.add(api.getcurrent())
            try:
                result, exc = api.get_hub().switch()
                if exc is None:
                    return result
                else:
                    api.getcurrent().throw(*exc)
            finally:
                self._waiters.discard(api.getcurrent())

    def ready(self):
        return len(self.items) > 0

    def full(self):
        # for consistency with Channel
        return False

    def waiting(self):
        return len(self._waiters)


class Channel(object):

    def __init__(self, max_size=0):
        self.max_size = max_size
        self.items = collections.deque()
        self._waiters = set()
        self._senders = set()

    def __nonzero__(self):
        return len(self.items)>0

    def __len__(self):
        return len(self.items)

    def __repr__(self):
        params = (self.__class__.__name__, hex(id(self)), self.max_size, len(self.items), len(self._waiters), len(self._senders))
        return '<%s at %s max=%s items[%d] _w[%s] _s[%s]>' % params

    def send(self, result=None, exc=None):
        if exc is not None and not isinstance(exc, tuple):
            exc = (exc, )
        if api.getcurrent() is api.get_hub().greenlet:
            self.items.append((result, exc))
            if self._waiters:
                api.get_hub().schedule_call_global(0, self._do_switch)
        else:
            self.items.append((result, exc))
            # note that send() does not work well with timeouts. if your timeout fires
            # after this point, the item will remain in the queue
            if self._waiters:
                api.get_hub().schedule_call_global(0, self._do_switch)
            if len(self.items) > self.max_size:
                self._senders.add(api.getcurrent())
                try:
                    api.get_hub().switch()
                finally:
                    self._senders.discard(api.getcurrent())

    def send_exception(self, *args):
        # the arguments are the same as for greenlet.throw
        return self.send(exc=args)

    def _do_switch(self):
        while True:
            if self._waiters and self.items:
                waiter = self._waiters.pop()
                result, exc = self.items.popleft()
                try:
                    waiter.switch((result, exc))
                except:
                    traceback.print_exc()
            elif self._senders and len(self.items) <= self.max_size:
                sender = self._senders.pop()
                try:
                    sender.switch()
                except:
                    traceback.print_exc()
            else:
                break

    def wait(self):
        if self.items:
            result, exc = self.items.popleft()
            if len(self.items) <= self.max_size:
                api.get_hub().schedule_call_global(0, self._do_switch)
            if exc is None:
                return result
            else:
                api.getcurrent().throw(*exc)
        else:
            if self._senders:
                api.get_hub().schedule_call_global(0, self._do_switch)
            self._waiters.add(api.getcurrent())
            try:
                result, exc = api.get_hub().switch()
                if exc is None:
                    return result
                else:
                    api.getcurrent().throw(*exc)
            finally:
                self._waiters.discard(api.getcurrent())

    def ready(self):
        return len(self.items) > 0

    def full(self):
        return len(self.items) >= self.max_size

    def waiting(self):
        return max(0, len(self._waiters) - len(self.items))


def queue(max_size=None):
    if max_size is None:
        return Queue()
    else:
        return Channel(max_size)


class Actor(object):
    """ A free-running coroutine that accepts and processes messages.

    Kind of the equivalent of an Erlang process, really.  It processes
    a queue of messages in the order that they were sent.  You must
    subclass this and implement your own version of :meth:`received`.

    The actor's reference count will never drop to zero while the
    coroutine exists; if you lose all references to the actor object
    it will never be freed.
    """
    def __init__(self, concurrency = 1):
        """ Constructs an Actor, kicking off a new coroutine to process the messages.

        The concurrency argument specifies how many messages the actor will try
        to process concurrently.  If it is 1, the actor will process messages
        serially.
        """
        self._mailbox = collections.deque()
        self._event = event()
        self._killer = api.spawn(self.run_forever)
        self._pool = CoroutinePool(min_size=0, max_size=concurrency)

    def run_forever(self):
        """ Loops forever, continually checking the mailbox. """
        while True:
            if not self._mailbox:
                self._event.wait()
                self._event = event()
            else:
                # leave the message in the mailbox until after it's
                # been processed so the event doesn't get triggered
                # while in the received method
                self._pool.execute_async(
                    self.received, self._mailbox[0])
                self._mailbox.popleft()

    def cast(self, message):
        """ Send a message to the actor.

        If the actor is busy, the message will be enqueued for later
        consumption.  There is no return value.

        >>> a = Actor()
        >>> a.received = lambda msg: msg
        >>> a.cast("hello")
        """
        self._mailbox.append(message)
        # if this is the only message, the coro could be waiting
        if len(self._mailbox) == 1:
            self._event.send()

    def received(self, message):
        """ Called to process each incoming message.

        The default implementation just raises an exception, so
        replace it with something useful!

        >>> class Greeter(Actor):
        ...     def received(self, (message, evt) ):
        ...         print "received", message
        ...         if evt: evt.send()
        ...
        >>> a = Greeter()

        This example uses events to synchronize between the actor and the main
        coroutine in a predictable manner, but this kinda defeats the point of
        the :class:`Actor`, so don't do it in a real application.

        >>> evt = event()
        >>> a.cast( ("message 1", evt) )
        >>> evt.wait()  # force it to run at this exact moment
        received message 1
        >>> evt.reset()
        >>> a.cast( ("message 2", None) )
        >>> a.cast( ("message 3", evt) )
        >>> evt.wait()
        received message 2
        received message 3

        >>> api.kill(a._killer)   # test cleanup
        """
        raise NotImplementedError()