use super::Feed;

use core::pin::Pin;

use futures_core::future::Future;

use futures_core::ready;

use futures_core::task::{Context, Poll};

use futures_sink::Sink;

/// Future for the [`send`](super::SinkExt::send) method.

#[derive(Debug)]

#[must_use = "futures do nothing unless you `.await` or poll them"]

pub struct Send<'a, Si: ?Sized, Item> {

    feed: Feed<'a, Si, Item>,

}

// Pinning is never projected to children

impl<Si: Unpin + ?Sized, Item> Unpin for Send<'_, Si, Item> {}

impl<'a, Si: Sink<Item> + Unpin + ?Sized, Item> Send<'a, Si, Item> {

    pub(super) fn new(sink: &'a mut Si, item: Item) -> Self {

        Self { feed: Feed::new(sink, item) }

    }

}

impl<Si: Sink<Item> + Unpin + ?Sized, Item> Future for Send<'_, Si, Item> {

    type Output = Result<(), Si::Error>;

    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {

        let this = &mut *self;

        if this.feed.is_item_pending() {

            ready!(Pin::new(&mut this.feed).poll(cx))?;

            debug_assert!(!this.feed.is_item_pending());

        }

        // we're done sending the item, but want to block on flushing the

        // sink

        ready!(this.feed.sink_pin_mut().poll_flush(cx))?;

        Poll::Ready(Ok(()))

    }

}