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    use core::fmt;
    use core::pin::Pin;
    use futures_core::future::Future;
    use futures_core::ready;
    use futures_core::stream::{FusedStream, Stream};
    use futures_core::task::{Context, Poll};
    #[cfg(feature = "sink")]
    use futures_sink::Sink;
    use pin_project_lite::pin_project;

    // FIXME: docs, tests

    pin_project! {
        /// Stream for the [`take_until`](super::StreamExt::take_until) method.
        #[must_use = "streams do nothing unless polled"]
        pub struct TakeUntil<St: Stream, Fut: Future> {
            #[pin]
            stream: St,
            // Contains the inner Future on start and None once the inner Future is resolved
            // or taken out by the user.
            #[pin]
            fut: Option<Fut>,
            // Contains fut's return value once fut is resolved
            fut_result: Option<Fut::Output>,
            // Whether the future was taken out by the user.
            free: bool,
        }
    }

    impl<St, Fut> fmt::Debug for TakeUntil<St, Fut>
    where
        St: Stream + fmt::Debug,
        St::Item: fmt::Debug,
        Fut: Future + fmt::Debug,
    {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            f.debug_struct("TakeUntil")
                .field("stream", &self.stream)
                .field("fut", &self.fut)
                .finish()
        }
    }

    impl<St, Fut> TakeUntil<St, Fut>
    where
        St: Stream,
        Fut: Future,
    {
        pub(super) fn new(stream: St, fut: Fut) -> Self {
            Self {
                stream,
                fut: Some(fut),
                fut_result: None,
                free: false,
            }
        }

        delegate_access_inner!(stream, St, ());

        /// Extract the stopping future out of the combinator.
        /// The future is returned only if it isn't resolved yet, ie. if the stream isn't stopped yet.
        /// Taking out the future means the combinator will be yielding
        /// elements from the wrapped stream without ever stopping it.
        pub fn take_future(&mut self) -> Option<Fut> {
            if self.fut.is_some() {
                self.free = true;
            }

            self.fut.take()
        }

        /// Once the stopping future is resolved, this method can be used
        /// to extract the value returned by the stopping future.
        ///
        /// This may be used to retrieve arbitrary data from the stopping
        /// future, for example a reason why the stream was stopped.
        ///
        /// This method will return `None` if the future isn't resolved yet,
        /// or if the result was already taken out.
        ///
        /// # Examples
        ///
        /// ```
        /// # futures::executor::block_on(async {
        /// use futures::future;
        /// use futures::stream::{self, StreamExt};
        /// use futures::task::Poll;
        ///
        /// let stream = stream::iter(1..=10);
        ///
        /// let mut i = 0;
        /// let stop_fut = future::poll_fn(|_cx| {
        ///     i += 1;
        ///     if i <= 5 {
        ///         Poll::Pending
        ///     } else {
        ///         Poll::Ready("reason")
        ///     }
        /// });
        ///
        /// let mut stream = stream.take_until(stop_fut);
        /// let _ = stream.by_ref().collect::<Vec<_>>().await;
        ///
        /// let result = stream.take_result().unwrap();
        /// assert_eq!(result, "reason");
        /// # });
        /// ```
        pub fn take_result(&mut self) -> Option<Fut::Output> {
            self.fut_result.take()
        }

        /// Whether the stream was stopped yet by the stopping future
        /// being resolved.
        pub fn is_stopped(&self) -> bool {
            !self.free && self.fut.is_none()
        }
    }

    impl<St, Fut> Stream for TakeUntil<St, Fut>
    where
        St: Stream,
        Fut: Future,
    {
        type Item = St::Item;

        fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<St::Item>> {
            let mut this = self.project();

            if let Some(f) = this.fut.as_mut().as_pin_mut() {
                if let Poll::Ready(result) = f.poll(cx) {
                    this.fut.set(None);
                    *this.fut_result = Some(result);
                }
            }

            if !*this.free && this.fut.is_none() {
                // Future resolved, inner stream stopped
                Poll::Ready(None)
            } else {
                // Future either not resolved yet or taken out by the user
                let item = ready!(this.stream.poll_next(cx));
                if item.is_none() {
                    this.fut.set(None);
                }
                Poll::Ready(item)
            }
        }

        fn size_hint(&self) -> (usize, Option<usize>) {
            if self.is_stopped() {
                return (0, Some(0));
            }

            self.stream.size_hint()
        }
    }

    impl<St, Fut> FusedStream for TakeUntil<St, Fut>
    where
        St: Stream,
        Fut: Future,
    {
        fn is_terminated(&self) -> bool {
            self.is_stopped()
        }
    }

    // Forwarding impl of Sink from the underlying stream
    #[cfg(feature = "sink")]
    impl<S, Fut, Item> Sink<Item> for TakeUntil<S, Fut>
    where
        S: Stream + Sink<Item>,
        Fut: Future,
    {
        type Error = S::Error;

        delegate_sink!(stream, Item);
    }