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use core::fmt;
use core::marker::PhantomData;
use core::pin::Pin;
use futures_core::ready;
use futures_core::stream::{FusedStream, Stream};
use futures_core::task::{Context, Poll};
use futures_sink::Sink;
use pin_project_lite::pin_project;
pin_project! {
/// Sink for the [`with_flat_map`](super::SinkExt::with_flat_map) method.
#[must_use = "sinks do nothing unless polled"]
pub struct WithFlatMap<Si, Item, U, St, F> {
#[pin]
sink: Si,
f: F,
#[pin]
stream: Option<St>,
buffer: Option<Item>,
_marker: PhantomData<fn(U)>,
}
}
impl<Si, Item, U, St, F> fmt::Debug for WithFlatMap<Si, Item, U, St, F>
where
Si: fmt::Debug,
St: fmt::Debug,
Item: fmt::Debug,
{
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("WithFlatMap")
.field("sink", &self.sink)
.field("stream", &self.stream)
.field("buffer", &self.buffer)
.finish()
}
}
impl<Si, Item, U, St, F> WithFlatMap<Si, Item, U, St, F>
where
Si: Sink<Item>,
F: FnMut(U) -> St,
St: Stream<Item = Result<Item, Si::Error>>,
{
pub(super) fn new(sink: Si, f: F) -> Self {
Self { sink, f, stream: None, buffer: None, _marker: PhantomData }
}
delegate_access_inner!(sink, Si, ());
fn try_empty_stream(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Si::Error>> {
let mut this = self.project();
if this.buffer.is_some() {
ready!(this.sink.as_mut().poll_ready(cx))?;
let item = this.buffer.take().unwrap();
this.sink.as_mut().start_send(item)?;
}
if let Some(mut some_stream) = this.stream.as_mut().as_pin_mut() {
while let Some(item) = ready!(some_stream.as_mut().poll_next(cx)?) {
match this.sink.as_mut().poll_ready(cx)? {
Poll::Ready(()) => this.sink.as_mut().start_send(item)?,
Poll::Pending => {
*this.buffer = Some(item);
return Poll::Pending;
}
};
}
}
this.stream.set(None);
Poll::Ready(Ok(()))
}
}
// Forwarding impl of Stream from the underlying sink
impl<S, Item, U, St, F> Stream for WithFlatMap<S, Item, U, St, F>
where
S: Stream + Sink<Item>,
F: FnMut(U) -> St,
St: Stream<Item = Result<Item, S::Error>>,
{
type Item = S::Item;
delegate_stream!(sink);
}
impl<S, Item, U, St, F> FusedStream for WithFlatMap<S, Item, U, St, F>
where
S: FusedStream + Sink<Item>,
F: FnMut(U) -> St,
St: Stream<Item = Result<Item, S::Error>>,
{
fn is_terminated(&self) -> bool {
self.sink.is_terminated()
}
}
impl<Si, Item, U, St, F> Sink<U> for WithFlatMap<Si, Item, U, St, F>
where
Si: Sink<Item>,
F: FnMut(U) -> St,
St: Stream<Item = Result<Item, Si::Error>>,
{
type Error = Si::Error;
fn poll_ready(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
self.try_empty_stream(cx)
}
fn start_send(self: Pin<&mut Self>, item: U) -> Result<(), Self::Error> {
let mut this = self.project();
assert!(this.stream.is_none());
this.stream.set(Some((this.f)(item)));
Ok(())
}
fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
ready!(self.as_mut().try_empty_stream(cx)?);
self.project().sink.poll_flush(cx)
}
fn poll_close(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
ready!(self.as_mut().try_empty_stream(cx)?);
self.project().sink.poll_close(cx)
}
}