ufotofu 0.12.5

Abstractions for lazily consuming and producing sequences
Documentation 
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use crate::{prelude::*, ConsumeLimitError};

/// A `Consumer` adaptor that limits the number of regular items accepted by the Consumer.
///
/// Use the [`into_inner`](`Limit::into_inner`) method or [`AsRef<C>`](AsRef) impl to access the wrapped consumer.
///
/// Created via the [`ConsumerExt::to_limit`] method.
///
/// <br/>Counterpart: the [`producer::Limit`] type.
#[derive(Copy, Clone, Hash, Ord, Eq, PartialEq, PartialOrd, Debug)]
pub struct Limit<C> {
    inner: C,
    remaining: usize,
}

impl<C> Limit<C> {
    pub(crate) fn new(inner: C, limit: usize) -> Self {
        Limit {
            inner,
            remaining: limit,
        }
    }

    /// Consumes `self` and returns the wrapped consumer.
    pub fn into_inner(self) -> C {
        self.inner
    }

    /// Returns the number of items that can still be consumed before returning an error.
    pub fn remaining(&self) -> usize {
        self.remaining
    }
}

impl<C> AsRef<C> for Limit<C> {
    fn as_ref(&self) -> &C {
        &self.inner
    }
}

impl<C: Consumer> Consumer for Limit<C> {
    type Item = C::Item;
    type Final = C::Final;
    type Error = ConsumeLimitError<C::Error>;

    async fn consume(&mut self, val: Either<Self::Item, Self::Final>) -> Result<(), Self::Error> {
        match val {
            Left(item) => match self.remaining.checked_sub(1) {
                None => Result::Err(ConsumeLimitError::LimitReached),
                Some(decremented) => {
                    self.remaining = decremented;
                    self.inner
                        .consume_item(item)
                        .await
                        .map_err(ConsumeLimitError::Inner)
                }
            },
            Right(fin) => self
                .inner
                .consume_final(fin)
                .await
                .map_err(ConsumeLimitError::Inner),
        }
    }

    async fn flush(&mut self) -> Result<(), Self::Error> {
        self.inner.flush().await.map_err(ConsumeLimitError::Inner)
    }
}

impl<C: BulkConsumer> BulkConsumer for Limit<C> {
    async fn expose_slots_gracefully<F, R>(&mut self, f: F) -> Result<R, (F, Self::Error)>
    where
        F: AsyncFnOnce(&mut [Self::Item]) -> (usize, R),
    {
        if self.remaining == 0 {
            return Err((f, ConsumeLimitError::LimitReached));
        }

        let mut f = Some(f);
        let mut remaining = self.remaining;

        let ret = self
            .inner
            .expose_slots(async |slots| {
                let len = remaining.min(slots.len());
                let inner_f = f.take().expect("This only runs once, so f is safe to take");
                let (consumed, returned) = inner_f(&mut slots[..len]).await;
                remaining -= consumed;
                (consumed, returned)
            })
            .await;
        self.remaining = remaining;

        match ret {
            Ok(r) => Ok(r),
            Err(error) => Err((
                f.take()
                    .expect("Wrapper closure wasn't called, so f is safe to take"),
                ConsumeLimitError::Inner(error),
            )),
        }
    }
}

#[cfg(test)]
mod tests {
    use crate::prelude::*;
    use crate::ConsumeLimitError;

    #[test]
    fn inner_error() {
        let mut c = consumer::error_immediately("internal_error").to_limit(20);
        pollster::block_on(async {
            assert_eq!(
                c.flush().await,
                Err(ConsumeLimitError::Inner("internal_error"))
            );
        });
    }
}