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

    use bytes::{Buf, BufMut, BytesMut};
    use std::{cmp, fmt, io, str, usize};

    /// A simple [`Decoder`] and [`Encoder`] implementation that splits up data into lines.
    ///
    /// [`Decoder`]: crate::codec::Decoder
    /// [`Encoder`]: crate::codec::Encoder
    #[derive(Clone, Debug, Eq, PartialEq, Ord, PartialOrd, Hash)]
    pub struct LinesCodec {
        // Stored index of the next index to examine for a `\n` character.
        // This is used to optimize searching.
        // For example, if `decode` was called with `abc`, it would hold `3`,
        // because that is the next index to examine.
        // The next time `decode` is called with `abcde\n`, the method will
        // only look at `de\n` before returning.
        next_index: usize,

        /// The maximum length for a given line. If `usize::MAX`, lines will be
        /// read until a `\n` character is reached.
        max_length: usize,

        /// Are we currently discarding the remainder of a line which was over
        /// the length limit?
        is_discarding: bool,
    }

    impl LinesCodec {
        /// Returns a `LinesCodec` for splitting up data into lines.
        ///
        /// # Note
        ///
        /// The returned `LinesCodec` will not have an upper bound on the length
        /// of a buffered line. See the documentation for [`new_with_max_length`]
        /// for information on why this could be a potential security risk.
        ///
        /// [`new_with_max_length`]: crate::codec::LinesCodec::new_with_max_length()
        pub fn new() -> LinesCodec {
            LinesCodec {
                next_index: 0,
                max_length: usize::MAX,
                is_discarding: false,
            }
        }

        /// Returns a `LinesCodec` with a maximum line length limit.
        ///
        /// If this is set, calls to `LinesCodec::decode` will return a
        /// [`LinesCodecError`] when a line exceeds the length limit. Subsequent calls
        /// will discard up to `limit` bytes from that line until a newline
        /// character is reached, returning `None` until the line over the limit
        /// has been fully discarded. After that point, calls to `decode` will
        /// function as normal.
        ///
        /// # Note
        ///
        /// Setting a length limit is highly recommended for any `LinesCodec` which
        /// will be exposed to untrusted input. Otherwise, the size of the buffer
        /// that holds the line currently being read is unbounded. An attacker could
        /// exploit this unbounded buffer by sending an unbounded amount of input
        /// without any `\n` characters, causing unbounded memory consumption.
        ///
        /// [`LinesCodecError`]: crate::codec::LinesCodecError
        pub fn new_with_max_length(max_length: usize) -> Self {
            LinesCodec {
                max_length,
                ..LinesCodec::new()
            }
        }

        /// Returns the maximum line length when decoding.
        ///
        /// ```
        /// use std::usize;
        /// use tokio_util::codec::LinesCodec;
        ///
        /// let codec = LinesCodec::new();
        /// assert_eq!(codec.max_length(), usize::MAX);
        /// ```
        /// ```
        /// use tokio_util::codec::LinesCodec;
        ///
        /// let codec = LinesCodec::new_with_max_length(256);
        /// assert_eq!(codec.max_length(), 256);
        /// ```
        pub fn max_length(&self) -> usize {
            self.max_length
        }
    }

    fn utf8(buf: &[u8]) -> Result<&str, io::Error> {
        str::from_utf8(buf)
            .map_err(|_| io::Error::new(io::ErrorKind::InvalidData, "Unable to decode input as UTF8"))
    }

    fn without_carriage_return(s: &[u8]) -> &[u8] {
        if let Some(&b'\r') = s.last() {
            &s[..s.len() - 1]
        } else {
            s
        }
    }

    impl Decoder for LinesCodec {
        type Item = String;
        type Error = LinesCodecError;

        fn decode(&mut self, buf: &mut BytesMut) -> Result<Option<String>, LinesCodecError> {
            loop {
                // Determine how far into the buffer we'll search for a newline. If
                // there's no max_length set, we'll read to the end of the buffer.
                let read_to = cmp::min(self.max_length.saturating_add(1), buf.len());

                let newline_offset = buf[self.next_index..read_to]
                    .iter()
                    .position(|b| *b == b'\n');

                match (self.is_discarding, newline_offset) {
                    (true, Some(offset)) => {
                        // If we found a newline, discard up to that offset and
                        // then stop discarding. On the next iteration, we'll try
                        // to read a line normally.
                        buf.advance(offset + self.next_index + 1);
                        self.is_discarding = false;
                        self.next_index = 0;
                    }
                    (true, None) => {
                        // Otherwise, we didn't find a newline, so we'll discard
                        // everything we read. On the next iteration, we'll continue
                        // discarding up to max_len bytes unless we find a newline.
                        buf.advance(read_to);
                        self.next_index = 0;
                        if buf.is_empty() {
                            return Ok(None);
                        }
                    }
                    (false, Some(offset)) => {
                        // Found a line!
                        let newline_index = offset + self.next_index;
                        self.next_index = 0;
                        let line = buf.split_to(newline_index + 1);
                        let line = &line[..line.len() - 1];
                        let line = without_carriage_return(line);
                        let line = utf8(line)?;
                        return Ok(Some(line.to_string()));
                    }
                    (false, None) if buf.len() > self.max_length => {
                        // Reached the maximum length without finding a
                        // newline, return an error and start discarding on the
                        // next call.
                        self.is_discarding = true;
                        return Err(LinesCodecError::MaxLineLengthExceeded);
                    }
                    (false, None) => {
                        // We didn't find a line or reach the length limit, so the next
                        // call will resume searching at the current offset.
                        self.next_index = read_to;
                        return Ok(None);
                    }
                }
            }
        }

        fn decode_eof(&mut self, buf: &mut BytesMut) -> Result<Option<String>, LinesCodecError> {
            Ok(match self.decode(buf)? {
                Some(frame) => Some(frame),
                None => {
                    // No terminating newline - return remaining data, if any
                    if buf.is_empty() || buf == &b"\r"[..] {
                        None
                    } else {
                        let line = buf.split_to(buf.len());
                        let line = without_carriage_return(&line);
                        let line = utf8(line)?;
                        self.next_index = 0;
                        Some(line.to_string())
                    }
                }
            })
        }
    }

    impl<T> Encoder<T> for LinesCodec
    where
        T: AsRef<str>,
    {
        type Error = LinesCodecError;

        fn encode(&mut self, line: T, buf: &mut BytesMut) -> Result<(), LinesCodecError> {
            let line = line.as_ref();
            buf.reserve(line.len() + 1);
            buf.put(line.as_bytes());
            buf.put_u8(b'\n');
            Ok(())
        }
    }

    impl Default for LinesCodec {
        fn default() -> Self {
            Self::new()
        }
    }

    /// An error occured while encoding or decoding a line.
    #[derive(Debug)]
    pub enum LinesCodecError {
        /// The maximum line length was exceeded.
        MaxLineLengthExceeded,
        /// An IO error occured.
        Io(io::Error),
    }

    impl fmt::Display for LinesCodecError {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            match self {
                LinesCodecError::MaxLineLengthExceeded => write!(f, "max line length exceeded"),
                LinesCodecError::Io(e) => write!(f, "{}", e),
            }
        }
    }

    impl From<io::Error> for LinesCodecError {
        fn from(e: io::Error) -> LinesCodecError {
            LinesCodecError::Io(e)
        }
    }

    impl std::error::Error for LinesCodecError {}