# Source code for scrapy.utils.defer

    """
    Helper functions for dealing with Twisted deferreds
    """
    import asyncio
    import inspect
    from asyncio import Future
    from functools import wraps
    from types import CoroutineType
    from typing import (
        Any,
        AsyncGenerator,
        AsyncIterable,
        AsyncIterator,
        Awaitable,
        Callable,
        Coroutine,
        Dict,
        Generator,
        Iterable,
        Iterator,
        List,
        Optional,
        Tuple,
        TypeVar,
        Union,
        cast,
        overload,
    )

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

    from scrapy.exceptions import IgnoreRequest
    from scrapy.utils.reactor import _get_asyncio_event_loop, is_asyncio_reactor_installed

    def defer_fail(_failure: Failure) -> Deferred:
        """Same as twisted.internet.defer.fail but delay calling errback until
        next reactor loop

        It delays by 100ms so reactor has a chance to go through readers and writers
        before attending pending delayed calls, so do not set delay to zero.
        """
        from twisted.internet import reactor

        d: Deferred = Deferred()
        reactor.callLater(0.1, d.errback, _failure)
        return d

    def defer_succeed(result: Any) -> Deferred:
        """Same as twisted.internet.defer.succeed but delay calling callback until
        next reactor loop

        It delays by 100ms so reactor has a chance to go through readers and writers
        before attending pending delayed calls, so do not set delay to zero.
        """
        from twisted.internet import reactor

        d: Deferred = Deferred()
        reactor.callLater(0.1, d.callback, result)
        return d

    def defer_result(result: Any) -> Deferred:
        if isinstance(result, Deferred):
            return result
        if isinstance(result, failure.Failure):
            return defer_fail(result)
        return defer_succeed(result)

    def mustbe_deferred(f: Callable, *args: Any, **kw: Any) -> Deferred:
        """Same as twisted.internet.defer.maybeDeferred, but delay calling
        callback/errback to next reactor loop
        """
        try:
            result = f(*args, **kw)
        # FIXME: Hack to avoid introspecting tracebacks. This to speed up
        # processing of IgnoreRequest errors which are, by far, the most common
        # exception in Scrapy - see #125
        except IgnoreRequest as e:
            return defer_fail(failure.Failure(e))
        except Exception:
            return defer_fail(failure.Failure())
        else:
            return defer_result(result)

    def parallel(
        iterable: Iterable, count: int, callable: Callable, *args: Any, **named: Any
    ) -> Deferred:
        """Execute a callable over the objects in the given iterable, in parallel,
        using no more than ``count`` concurrent calls.

        Taken from: https://jcalderone.livejournal.com/24285.html
        """
        coop = Cooperator()
        work = (callable(elem, *args, **named) for elem in iterable)
        return DeferredList([coop.coiterate(work) for _ in range(count)])

    class _AsyncCooperatorAdapter(Iterator):
        """A class that wraps an async iterable into a normal iterator suitable
        for using in Cooperator.coiterate(). As it's only needed for parallel_async(),
        it calls the callable directly in the callback, instead of providing a more
        generic interface.

        On the outside, this class behaves as an iterator that yields Deferreds.
        Each Deferred is fired with the result of the callable which was called on
        the next result from aiterator. It raises StopIteration when aiterator is
        exhausted, as expected.

        Cooperator calls __next__() multiple times and waits on the Deferreds
        returned from it. As async generators (since Python 3.8) don't support
        awaiting on __anext__() several times in parallel, we need to serialize
        this. It's done by storing the Deferreds returned from __next__() and
        firing the oldest one when a result from __anext__() is available.

        The workflow:
        1. When __next__() is called for the first time, it creates a Deferred, stores it
        in self.waiting_deferreds and returns it. It also makes a Deferred that will wait
        for self.aiterator.__anext__() and puts it into self.anext_deferred.
        2. If __next__() is called again before self.anext_deferred fires, more Deferreds
        are added to self.waiting_deferreds.
        3. When self.anext_deferred fires, it either calls _callback() or _errback(). Both
        clear self.anext_deferred.
        3.1. _callback() calls the callable passing the result value that it takes, pops a
        Deferred from self.waiting_deferreds, and if the callable result was a Deferred, it
        chains those Deferreds so that the waiting Deferred will fire when the result
        Deferred does, otherwise it fires it directly. This causes one awaiting task to
        receive a result. If self.waiting_deferreds is still not empty, new __anext__() is
        called and self.anext_deferred is populated.
        3.2. _errback() checks the exception class. If it's StopAsyncIteration it means
        self.aiterator is exhausted and so it sets self.finished and fires all
        self.waiting_deferreds. Other exceptions are propagated.
        4. If __next__() is called after __anext__() was handled, then if self.finished is
        True, it raises StopIteration, otherwise it acts like in step 2, but if
        self.anext_deferred is now empty is also populates it with a new __anext__().

        Note that CooperativeTask ignores the value returned from the Deferred that it waits
        for, so we fire them with None when needed.

        It may be possible to write an async iterator-aware replacement for
        Cooperator/CooperativeTask and use it instead of this adapter to achieve the same
        goal.
        """

        def __init__(
            self,
            aiterable: AsyncIterable,
            callable: Callable,
            *callable_args: Any,
            **callable_kwargs: Any,
        ):
            self.aiterator: AsyncIterator = aiterable.__aiter__()
            self.callable: Callable = callable
            self.callable_args: Tuple[Any, ...] = callable_args
            self.callable_kwargs: Dict[str, Any] = callable_kwargs
            self.finished: bool = False
            self.waiting_deferreds: List[Deferred] = []
            self.anext_deferred: Optional[Deferred] = None

        def _callback(self, result: Any) -> None:
            # This gets called when the result from aiterator.__anext__() is available.
            # It calls the callable on it and sends the result to the oldest waiting Deferred
            # (by chaining if the result is a Deferred too or by firing if not).
            self.anext_deferred = None
            result = self.callable(result, *self.callable_args, **self.callable_kwargs)
            d = self.waiting_deferreds.pop(0)
            if isinstance(result, Deferred):
                result.chainDeferred(d)
            else:
                d.callback(None)
            if self.waiting_deferreds:
                self._call_anext()

        def _errback(self, failure: Failure) -> None:
            # This gets called on any exceptions in aiterator.__anext__().
            # It handles StopAsyncIteration by stopping the iteration and reraises all others.
            self.anext_deferred = None
            failure.trap(StopAsyncIteration)
            self.finished = True
            for d in self.waiting_deferreds:
                d.callback(None)

        def _call_anext(self) -> None:
            # This starts waiting for the next result from aiterator.
            # If aiterator is exhausted, _errback will be called.
            self.anext_deferred = deferred_from_coro(self.aiterator.__anext__())
            self.anext_deferred.addCallbacks(self._callback, self._errback)

        def __next__(self) -> Deferred:
            # This puts a new Deferred into self.waiting_deferreds and returns it.
            # It also calls __anext__() if needed.
            if self.finished:
                raise StopIteration
            d: Deferred = Deferred()
            self.waiting_deferreds.append(d)
            if not self.anext_deferred:
                self._call_anext()
            return d

    def parallel_async(
        async_iterable: AsyncIterable,
        count: int,
        callable: Callable,
        *args: Any,
        **named: Any,
    ) -> Deferred:
        """Like parallel but for async iterators"""
        coop = Cooperator()
        work = _AsyncCooperatorAdapter(async_iterable, callable, *args, **named)
        dl: Deferred = DeferredList([coop.coiterate(work) for _ in range(count)])
        return dl

    def process_chain(
        callbacks: Iterable[Callable], input: Any, *a: Any, **kw: Any
    ) -> Deferred:
        """Return a Deferred built by chaining the given callbacks"""
        d: Deferred = Deferred()
        for x in callbacks:
            d.addCallback(x, *a, **kw)
        d.callback(input)
        return d

    def process_chain_both(
        callbacks: Iterable[Callable],
        errbacks: Iterable[Callable],
        input: Any,
        *a: Any,
        **kw: Any,
    ) -> Deferred:
        """Return a Deferred built by chaining the given callbacks and errbacks"""
        d: Deferred = Deferred()
        for cb, eb in zip(callbacks, errbacks):
            d.addCallbacks(
                callback=cb,
                errback=eb,
                callbackArgs=a,
                callbackKeywords=kw,
                errbackArgs=a,
                errbackKeywords=kw,
            )
        if isinstance(input, failure.Failure):
            d.errback(input)
        else:
            d.callback(input)
        return d

    def process_parallel(
        callbacks: Iterable[Callable], input: Any, *a: Any, **kw: Any
    ) -> Deferred:
        """Return a Deferred with the output of all successful calls to the given
        callbacks
        """
        dfds = [defer.succeed(input).addCallback(x, *a, **kw) for x in callbacks]
        d: Deferred = DeferredList(dfds, fireOnOneErrback=True, consumeErrors=True)
        d.addCallbacks(lambda r: [x[1] for x in r], lambda f: f.value.subFailure)
        return d

    def iter_errback(
        iterable: Iterable, errback: Callable, *a: Any, **kw: Any
    ) -> Generator:
        """Wraps an iterable calling an errback if an error is caught while
        iterating it.
        """
        it = iter(iterable)
        while True:
            try:
                yield next(it)
            except StopIteration:
                break
            except Exception:
                errback(failure.Failure(), *a, **kw)

    async def aiter_errback(
        aiterable: AsyncIterable, errback: Callable, *a: Any, **kw: Any
    ) -> AsyncGenerator:
        """Wraps an async iterable calling an errback if an error is caught while
        iterating it. Similar to scrapy.utils.defer.iter_errback()
        """
        it = aiterable.__aiter__()
        while True:
            try:
                yield await it.__anext__()
            except StopAsyncIteration:
                break
            except Exception:
                errback(failure.Failure(), *a, **kw)

    _CT = TypeVar("_CT", bound=Union[Awaitable, CoroutineType, Future])
    _T = TypeVar("_T")

    @overload
    def deferred_from_coro(o: _CT) -> Deferred:
        ...

    @overload
    def deferred_from_coro(o: _T) -> _T:
        ...

    def deferred_from_coro(o: _T) -> Union[Deferred, _T]:
        """Converts a coroutine into a Deferred, or returns the object as is if it isn't a coroutine"""
        if isinstance(o, Deferred):
            return o
        if asyncio.isfuture(o) or inspect.isawaitable(o):
            if not is_asyncio_reactor_installed():
                # wrapping the coroutine directly into a Deferred, this doesn't work correctly with coroutines
                # that use asyncio, e.g. "await asyncio.sleep(1)"
                return ensureDeferred(cast(Coroutine[Deferred, Any, Any], o))
            # wrapping the coroutine into a Future and then into a Deferred, this requires AsyncioSelectorReactor
            event_loop = _get_asyncio_event_loop()
            return Deferred.fromFuture(asyncio.ensure_future(o, loop=event_loop))
        return o

    def deferred_f_from_coro_f(coro_f: Callable[..., Coroutine]) -> Callable:
        """Converts a coroutine function into a function that returns a Deferred.

        The coroutine function will be called at the time when the wrapper is called. Wrapper args will be passed to it.
        This is useful for callback chains, as callback functions are called with the previous callback result.
        """

        @wraps(coro_f)
        def f(*coro_args: Any, **coro_kwargs: Any) -> Any:
            return deferred_from_coro(coro_f(*coro_args, **coro_kwargs))

        return f

    def maybeDeferred_coro(f: Callable, *args: Any, **kw: Any) -> Deferred:
        """Copy of defer.maybeDeferred that also converts coroutines to Deferreds."""
        try:
            result = f(*args, **kw)
        except:  # noqa: E722
            return defer.fail(failure.Failure(captureVars=Deferred.debug))

        if isinstance(result, Deferred):
            return result
        if asyncio.isfuture(result) or inspect.isawaitable(result):
            return deferred_from_coro(result)
        if isinstance(result, failure.Failure):
            return defer.fail(result)
        return defer.succeed(result)

    def deferred_to_future(d: Deferred) -> Future:
        """
        .. versionadded:: 2.6.0

        Return an :class:`asyncio.Future` object that wraps *d*.

        When :ref:`using the asyncio reactor <install-asyncio>`, you cannot await
        on :class:`~twisted.internet.defer.Deferred` objects from :ref:`Scrapy
        callables defined as coroutines <coroutine-support>`, you can only await on
        ``Future`` objects. Wrapping ``Deferred`` objects into ``Future`` objects
        allows you to wait on them::

            class MySpider(Spider):
                ...
                async def parse(self, response):
                    additional_request = scrapy.Request('https://example.org/price')
                    deferred = self.crawler.engine.download(additional_request)
                    additional_response = await deferred_to_future(deferred)
        """
        return d.asFuture(_get_asyncio_event_loop())

    def maybe_deferred_to_future(d: Deferred) -> Union[Deferred, Future]:
        """
        .. versionadded:: 2.6.0

        Return *d* as an object that can be awaited from a :ref:`Scrapy callable
        defined as a coroutine <coroutine-support>`.

        What you can await in Scrapy callables defined as coroutines depends on the
        value of :setting:`TWISTED_REACTOR`:

        -   When not using the asyncio reactor, you can only await on
            :class:`~twisted.internet.defer.Deferred` objects.

        -   When :ref:`using the asyncio reactor <install-asyncio>`, you can only
            await on :class:`asyncio.Future` objects.

        If you want to write code that uses ``Deferred`` objects but works with any
        reactor, use this function on all ``Deferred`` objects::

            class MySpider(Spider):
                ...
                async def parse(self, response):
                    additional_request = scrapy.Request('https://example.org/price')
                    deferred = self.crawler.engine.download(additional_request)
                    additional_response = await maybe_deferred_to_future(deferred)
        """
        if not is_asyncio_reactor_installed():
            return d
        return deferred_to_future(d)