use core::fmt;
use core::marker::PhantomData;
use core::pin::Pin;
use futures_core::stream::{Stream, FusedStream};
use futures_core::task::{Context, Poll};
use futures_sink::Sink;
use pin_utils::{unsafe_pinned, unsafe_unpinned};
#[must_use = "sinks do nothing unless polled"]
pub struct WithFlatMap<Si, Item, U, St, F> {
sink: Si,
f: F,
stream: Option<St>,
buffer: Option<Item>,
_marker: PhantomData<fn(U)>,
}
impl<Si, Item, U, St, F> Unpin for WithFlatMap<Si, Item, U, St, F>
where
Si: Unpin,
St: Unpin,
{}
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>>,
{
unsafe_pinned!(sink: Si);
unsafe_unpinned!(f: F);
unsafe_pinned!(stream: Option<St>);
pub(super) fn new(sink: Si, f: F) -> Self {
WithFlatMap {
sink,
f,
stream: None,
buffer: None,
_marker: PhantomData,
}
}
pub fn get_ref(&self) -> &Si {
&self.sink
}
pub fn get_mut(&mut self) -> &mut Si {
&mut self.sink
}
pub fn get_pin_mut(self: Pin<&mut Self>) -> Pin<&mut Si> {
self.sink()
}
pub fn into_inner(self) -> Si {
self.sink
}
fn try_empty_stream(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
) -> Poll<Result<(), Si::Error>> {
let WithFlatMap { sink, stream, buffer, .. } =
unsafe { self.get_unchecked_mut() };
let mut sink = unsafe { Pin::new_unchecked(sink) };
let mut stream = unsafe { Pin::new_unchecked(stream) };
if buffer.is_some() {
ready!(sink.as_mut().poll_ready(cx))?;
let item = buffer.take().unwrap();
sink.as_mut().start_send(item)?;
}
if let Some(mut some_stream) = stream.as_mut().as_pin_mut() {
while let Some(item) = ready!(some_stream.as_mut().poll_next(cx)?) {
match sink.as_mut().poll_ready(cx)? {
Poll::Ready(()) => sink.as_mut().start_send(item)?,
Poll::Pending => {
*buffer = Some(item);
return Poll::Pending;
}
};
}
}
stream.set(None);
Poll::Ready(Ok(()))
}
}
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;
fn poll_next(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
) -> Poll<Option<S::Item>> {
self.sink().poll_next(cx)
}
fn size_hint(&self) -> (usize, Option<usize>) {
self.sink.size_hint()
}
}
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(
mut self: Pin<&mut Self>,
item: U,
) -> Result<(), Self::Error> {
assert!(self.stream.is_none());
let stream = (self.as_mut().f())(item);
self.stream().set(Some(stream));
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.as_mut().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.as_mut().sink().poll_close(cx)
}
}