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    use crate::codec::decoder::Decoder;
    use crate::codec::encoder::Encoder;

    use futures_core::Stream;
    use tokio::io::{AsyncRead, AsyncWrite};

    use bytes::BytesMut;
    use futures_core::ready;
    use futures_sink::Sink;
    use log::trace;
    use pin_project_lite::pin_project;
    use std::borrow::{Borrow, BorrowMut};
    use std::io;
    use std::pin::Pin;
    use std::task::{Context, Poll};

    pin_project! {
        #[derive(Debug)]
        pub(crate) struct FramedImpl<T, U, State> {
            #[pin]
            pub(crate) inner: T,
            pub(crate) state: State,
            pub(crate) codec: U,
        }
    }

    const INITIAL_CAPACITY: usize = 8 * 1024;
    const BACKPRESSURE_BOUNDARY: usize = INITIAL_CAPACITY;

    pub(crate) struct ReadFrame {
        pub(crate) eof: bool,
        pub(crate) is_readable: bool,
        pub(crate) buffer: BytesMut,
    }

    pub(crate) struct WriteFrame {
        pub(crate) buffer: BytesMut,
    }

    #[derive(Default)]
    pub(crate) struct RWFrames {
        pub(crate) read: ReadFrame,
        pub(crate) write: WriteFrame,
    }

    impl Default for ReadFrame {
        fn default() -> Self {
            Self {
                eof: false,
                is_readable: false,
                buffer: BytesMut::with_capacity(INITIAL_CAPACITY),
            }
        }
    }

    impl Default for WriteFrame {
        fn default() -> Self {
            Self {
                buffer: BytesMut::with_capacity(INITIAL_CAPACITY),
            }
        }
    }

    impl From<BytesMut> for ReadFrame {
        fn from(mut buffer: BytesMut) -> Self {
            let size = buffer.capacity();
            if size < INITIAL_CAPACITY {
                buffer.reserve(INITIAL_CAPACITY - size);
            }

            Self {
                buffer,
                is_readable: size > 0,
                eof: false,
            }
        }
    }

    impl From<BytesMut> for WriteFrame {
        fn from(mut buffer: BytesMut) -> Self {
            let size = buffer.capacity();
            if size < INITIAL_CAPACITY {
                buffer.reserve(INITIAL_CAPACITY - size);
            }

            Self { buffer }
        }
    }

    impl Borrow<ReadFrame> for RWFrames {
        fn borrow(&self) -> &ReadFrame {
            &self.read
        }
    }
    impl BorrowMut<ReadFrame> for RWFrames {
        fn borrow_mut(&mut self) -> &mut ReadFrame {
            &mut self.read
        }
    }
    impl Borrow<WriteFrame> for RWFrames {
        fn borrow(&self) -> &WriteFrame {
            &self.write
        }
    }
    impl BorrowMut<WriteFrame> for RWFrames {
        fn borrow_mut(&mut self) -> &mut WriteFrame {
            &mut self.write
        }
    }
    impl<T, U, R> Stream for FramedImpl<T, U, R>
    where
        T: AsyncRead,
        U: Decoder,
        R: BorrowMut<ReadFrame>,
    {
        type Item = Result<U::Item, U::Error>;

        fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
            use crate::util::poll_read_buf;

            let mut pinned = self.project();
            let state: &mut ReadFrame = pinned.state.borrow_mut();
            loop {
                // Repeatedly call `decode` or `decode_eof` as long as it is
                // "readable". Readable is defined as not having returned `None`. If
                // the upstream has returned EOF, and the decoder is no longer
                // readable, it can be assumed that the decoder will never become
                // readable again, at which point the stream is terminated.
                if state.is_readable {
                    if state.eof {
                        let frame = pinned.codec.decode_eof(&mut state.buffer)?;
                        return Poll::Ready(frame.map(Ok));
                    }

                    trace!("attempting to decode a frame");

                    if let Some(frame) = pinned.codec.decode(&mut state.buffer)? {
                        trace!("frame decoded from buffer");
                        return Poll::Ready(Some(Ok(frame)));
                    }

                    state.is_readable = false;
                }

                assert!(!state.eof);

                // Otherwise, try to read more data and try again. Make sure we've
                // got room for at least one byte to read to ensure that we don't
                // get a spurious 0 that looks like EOF
                state.buffer.reserve(1);
                let bytect = match poll_read_buf(pinned.inner.as_mut(), cx, &mut state.buffer)? {
                    Poll::Ready(ct) => ct,
                    Poll::Pending => return Poll::Pending,
                };
                if bytect == 0 {
                    state.eof = true;
                }

                state.is_readable = true;
            }
        }
    }

    impl<T, I, U, W> Sink<I> for FramedImpl<T, U, W>
    where
        T: AsyncWrite,
        U: Encoder<I>,
        U::Error: From<io::Error>,
        W: BorrowMut<WriteFrame>,
    {
        type Error = U::Error;

        fn poll_ready(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
            if self.state.borrow().buffer.len() >= BACKPRESSURE_BOUNDARY {
                self.as_mut().poll_flush(cx)
            } else {
                Poll::Ready(Ok(()))
            }
        }

        fn start_send(self: Pin<&mut Self>, item: I) -> Result<(), Self::Error> {
            let pinned = self.project();
            pinned
                .codec
                .encode(item, &mut pinned.state.borrow_mut().buffer)?;
            Ok(())
        }

        fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
            use crate::util::poll_write_buf;
            trace!("flushing framed transport");
            let mut pinned = self.project();

            while !pinned.state.borrow_mut().buffer.is_empty() {
                let WriteFrame { buffer } = pinned.state.borrow_mut();
                trace!("writing; remaining={}", buffer.len());

                let n = ready!(poll_write_buf(pinned.inner.as_mut(), cx, buffer))?;

                if n == 0 {
                    return Poll::Ready(Err(io::Error::new(
                        io::ErrorKind::WriteZero,
                        "failed to \
                         write frame to transport",
                    )
                    .into()));
                }
            }

            // Try flushing the underlying IO
            ready!(pinned.inner.poll_flush(cx))?;

            trace!("framed transport flushed");
            Poll::Ready(Ok(()))
        }

        fn poll_close(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
            ready!(self.as_mut().poll_flush(cx))?;
            ready!(self.project().inner.poll_shutdown(cx))?;

            Poll::Ready(Ok(()))
        }
    }