use {Poll, Async, Future, AsyncSink};
use sink::Sink;

/// Future for the `Sink::send` combinator, which sends a value to a sink and
/// then waits until the sink has fully flushed.
#[derive(Debug)]
#[must_use = "futures do nothing unless polled"]
pub struct Send<S: Sink> {
    sink: Option<S>,
    item: Option<S::SinkItem>,
}

pub fn new<S: Sink>(sink: S, item: S::SinkItem) -> Send<S> {
    Send {
        sink: Some(sink),
        item: Some(item),
    }
}

impl<S: Sink> Send<S> {
    /// Get a shared reference to the inner sink.
    pub fn get_ref(&self) -> &S {
        self.sink.as_ref().take().expect("Attempted Send::get_ref after completion")
    }

    /// Get a mutable reference to the inner sink.
    pub fn get_mut(&mut self) -> &mut S {
        self.sink.as_mut().take().expect("Attempted Send::get_mut after completion")
    }

    fn sink_mut(&mut self) -> &mut S {
        self.sink.as_mut().take().expect("Attempted to poll Send after completion")
    }

    fn take_sink(&mut self) -> S {
        self.sink.take().expect("Attempted to poll Send after completion")
    }
}

impl<S: Sink> Future for Send<S> {
    type Item = S;
    type Error = S::SinkError;

    fn poll(&mut self) -> Poll<S, S::SinkError> {
        if let Some(item) = self.item.take() {
            if let AsyncSink::NotReady(item) = self.sink_mut().start_send(item)? {
                self.item = Some(item);
                return Ok(Async::NotReady);
            }
        }

        // we're done sending the item, but want to block on flushing the
        // sink
        try_ready!(self.sink_mut().poll_complete());

        // now everything's emptied, so return the sink for further use
        Ok(Async::Ready(self.take_sink()))
    }
}