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use futures_lite::{AsyncRead, AsyncWrite};
use std::io;
use std::pin::Pin;
use std::task::{Context, Poll};

#[derive(Clone, Debug, PartialEq)]
/// Duplex IO stream from reader and writer halves.
///
/// Convert an AsyncRead reader and AsyncWrite writer into a
/// AsyncRead + AsyncWrite stream
pub struct Duplex<R, W>
where
    R: AsyncRead + Send + Unpin + 'static,
    W: AsyncWrite + Send + Unpin + 'static,
{
    reader: R,
    writer: W,
}

impl<R, W> Duplex<R, W>
where
    R: AsyncRead + Send + Unpin + 'static,
    W: AsyncWrite + Send + Unpin + 'static,
{
    /// Create a new Duplex stream from a reader and a writer.
    pub fn new(reader: R, writer: W) -> Self {
        Self { reader, writer }
    }
}

impl<R, W> AsyncRead for Duplex<R, W>
where
    R: AsyncRead + Send + Unpin + 'static,
    W: AsyncWrite + Send + Unpin + 'static,
{
    fn poll_read(
        mut self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        buf: &mut [u8],
    ) -> Poll<io::Result<usize>> {
        Pin::new(&mut self.reader).poll_read(cx, buf)
    }
}

impl<R, W> AsyncWrite for Duplex<R, W>
where
    R: AsyncRead + Send + Unpin + 'static,
    W: AsyncWrite + Send + Unpin + 'static,
{
    fn poll_write(
        mut self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        buf: &[u8],
    ) -> Poll<io::Result<usize>> {
        Pin::new(&mut self.writer).poll_write(cx, buf)
    }

    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
        Pin::new(&mut self.writer).poll_flush(cx)
    }

    fn poll_close(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
        Pin::new(&mut self.writer).poll_close(cx)
    }
}