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    use crate::io::util::read_line::read_line_internal;
    use crate::io::AsyncBufRead;

    use pin_project_lite::pin_project;
    use std::io;
    use std::mem;
    use std::pin::Pin;
    use std::task::{Context, Poll};

    pin_project! {
        /// Read lines from an [`AsyncBufRead`].
        ///
        /// A `Lines` can be turned into a `Stream` with [`LinesStream`].
        ///
        /// This type is usually created using the [`lines`] method.
        ///
        /// [`AsyncBufRead`]: crate::io::AsyncBufRead
        /// [`LinesStream`]: https://docs.rs/tokio-stream/0.1/tokio_stream/wrappers/struct.LinesStream.html
        /// [`lines`]: crate::io::AsyncBufReadExt::lines
        #[derive(Debug)]
        #[must_use = "streams do nothing unless polled"]
        #[cfg_attr(docsrs, doc(cfg(feature = "io-util")))]
        pub struct Lines<R> {
            #[pin]
            reader: R,
            buf: String,
            bytes: Vec<u8>,
            read: usize,
        }
    }

    pub(crate) fn lines<R>(reader: R) -> Lines<R>
    where
        R: AsyncBufRead,
    {
        Lines {
            reader,
            buf: String::new(),
            bytes: Vec::new(),
            read: 0,
        }
    }

    impl<R> Lines<R>
    where
        R: AsyncBufRead + Unpin,
    {
        /// Returns the next line in the stream.
        ///
        /// # Examples
        ///
        /// ```
        /// # use tokio::io::AsyncBufRead;
        /// use tokio::io::AsyncBufReadExt;
        ///
        /// # async fn dox(my_buf_read: impl AsyncBufRead + Unpin) -> std::io::Result<()> {
        /// let mut lines = my_buf_read.lines();
        ///
        /// while let Some(line) = lines.next_line().await? {
        ///     println!("length = {}", line.len())
        /// }
        /// # Ok(())
        /// # }
        /// ```
        pub async fn next_line(&mut self) -> io::Result<Option<String>> {
            use crate::future::poll_fn;

            poll_fn(|cx| Pin::new(&mut *self).poll_next_line(cx)).await
        }

        /// Obtain a mutable reference to the underlying reader
        pub fn get_mut(&mut self) -> &mut R {
            &mut self.reader
        }

        /// Obtain a reference to the underlying reader
        pub fn get_ref(&mut self) -> &R {
            &self.reader
        }

        /// Unwraps this `Lines<R>`, returning the underlying reader.
        ///
        /// Note that any leftover data in the internal buffer is lost.
        /// Therefore, a following read from the underlying reader may lead to data loss.
        pub fn into_inner(self) -> R {
            self.reader
        }
    }

    impl<R> Lines<R>
    where
        R: AsyncBufRead,
    {
        /// Polls for the next line in the stream.
        ///
        /// This method returns:
        ///
        ///  * `Poll::Pending` if the next line is not yet available.
        ///  * `Poll::Ready(Ok(Some(line)))` if the next line is available.
        ///  * `Poll::Ready(Ok(None))` if there are no more lines in this stream.
        ///  * `Poll::Ready(Err(err))` if an IO error occurred while reading the next line.
        ///
        /// When the method returns `Poll::Pending`, the `Waker` in the provided
        /// `Context` is scheduled to receive a wakeup when more bytes become
        /// available on the underlying IO resource.
        ///
        /// Note that on multiple calls to `poll_next_line`, only the `Waker` from
        /// the `Context` passed to the most recent call is scheduled to receive a
        /// wakeup.
        pub fn poll_next_line(
            self: Pin<&mut Self>,
            cx: &mut Context<'_>,
        ) -> Poll<io::Result<Option<String>>> {
            let me = self.project();

            let n = ready!(read_line_internal(me.reader, cx, me.buf, me.bytes, me.read))?;
            debug_assert_eq!(*me.read, 0);

            if n == 0 && me.buf.is_empty() {
                return Poll::Ready(Ok(None));
            }

            if me.buf.ends_with('\n') {
                me.buf.pop();

                if me.buf.ends_with('\r') {
                    me.buf.pop();
                }
            }

            Poll::Ready(Ok(Some(mem::replace(me.buf, String::new()))))
        }
    }

    #[cfg(test)]
    mod tests {
        use super::*;

        #[test]
        fn assert_unpin() {
            crate::is_unpin::<Lines<()>>();
        }
    }