ufotofu 0.12.0

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

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

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

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

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

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

impl<P: Producer> Producer for Limit<P> {
    type Item = P::Item;
    type Final = P::Final;
    type Error = ProduceLimitError<P::Error>;

    async fn produce(&mut self) -> Result<Either<Self::Item, Self::Final>, Self::Error> {
        match self.remaining.checked_sub(1) {
            None => Result::Err(ProduceLimitError::LimitReached),
            Some(decremented) => {
                self.remaining = decremented;
                self.inner
                    .produce()
                    .await
                    .map_err(|err| ProduceLimitError::Inner(err))
            }
        }
    }

    async fn slurp(&mut self) -> Result<(), Self::Error> {
        self.inner
            .slurp()
            .await
            .map_err(|err| ProduceLimitError::Inner(err))
    }
}

impl<P: BulkProducer> BulkProducer for Limit<P> {
    async fn expose_items_gracefully<F, R>(
        &mut self,
        f: F,
    ) -> Result<Either<R, (F, Self::Final)>, (F, Self::Error)>
    where
        F: AsyncFnOnce(&[Self::Item]) -> (usize, R),
    {
        if self.remaining == 0 {
            return Err((f, ProduceLimitError::LimitReached));
        }

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

        let ret = self
            .inner
            .expose_items(async |items| {
                let len = remaining.min(items.len());
                remaining = remaining - len;
                let inner_f = f
                    .take()
                    .expect("This should only run once, so f should be safe to take");
                inner_f(&items[..len]).await
            })
            .await;
        self.remaining = remaining;

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

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

    #[test]
    fn inner_error() {
        let mut p = producer::error_immediately("internal_error").to_limit(20);
        pollster::block_on(async {
            assert_eq!(
                p.produce().await,
                Err(ProduceLimitError::Inner("internal_error"))
            );
        });
    }
}