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use super::Consumer;
use crate::concurrent_stream::ConsumerState;
use crate::prelude::*;
use core::future::{ready, Ready};
use core::num::NonZeroUsize;
use core::pin::pin;
use futures_lite::{Stream, StreamExt};
/// A concurrent for each implementation from a `Stream`
#[pin_project::pin_project]
#[derive(Debug)]
pub struct FromStream<S: Stream> {
#[pin]
stream: S,
}
impl<S: Stream> FromStream<S> {
pub(crate) fn new(stream: S) -> Self {
Self { stream }
}
}
impl<S> ConcurrentStream for FromStream<S>
where
S: Stream,
{
type Item = S::Item;
type Future = Ready<Self::Item>;
async fn drive<C>(self, consumer: C) -> C::Output
where
C: Consumer<Self::Item, Self::Future>,
{
let mut iter = pin!(self.stream);
let mut consumer = pin!(consumer);
// Concurrently progress the consumer as well as the stream. Whenever
// there is an item from the stream available, we submit it to the
// consumer and we wait.
//
// NOTE(yosh): we're relying on the fact that `Stream::next` can be
// dropped and recreated freely. That's also true for
// `Consumer::progress`; though that is intentional. It should be
// possible to write a combinator which does not drop the `Stream::next`
// future repeatedly. However for now we're happy to rely on this
// property here.
loop {
// Drive the stream forward
let a = async {
let item = iter.next().await;
State::Item(item)
};
// Drive the consumer forward
let b = async {
let control_flow = consumer.as_mut().progress().await;
State::Progress(control_flow)
};
// If an item is available, submit it to the consumer and wait for
// it to be ready.
match (b, a).race().await {
State::Progress(control_flow) => match control_flow {
ConsumerState::Break => break,
ConsumerState::Continue => continue,
ConsumerState::Empty => match iter.next().await {
Some(item) => match consumer.as_mut().send(ready(item)).await {
ConsumerState::Break => break,
ConsumerState::Empty | ConsumerState::Continue => continue,
},
None => break,
},
},
State::Item(Some(item)) => match consumer.as_mut().send(ready(item)).await {
ConsumerState::Break => break,
ConsumerState::Empty | ConsumerState::Continue => continue,
},
State::Item(None) => break,
}
}
// We will no longer receive items from the underlying stream, which
// means we're ready to wait for the consumer to finish up.
consumer.as_mut().flush().await
}
fn concurrency_limit(&self) -> Option<NonZeroUsize> {
None
}
fn size_hint(&self) -> (usize, Option<usize>) {
self.stream.size_hint()
}
}
enum State<T> {
Progress(super::ConsumerState),
Item(T),
}