use bytes::{BufMut, BytesMut};
use tokio_io::_tokio_codec::{Encoder, Decoder};
use std::{io, str};

/// A simple `Codec` implementation that splits up data into lines.
#[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,
}

impl LinesCodec {
    /// Returns a `LinesCodec` for splitting up data into lines.
    pub fn new() -> LinesCodec {
        LinesCodec { next_index: 0 }
    }
}

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 = io::Error;

    fn decode(&mut self, buf: &mut BytesMut) -> Result<Option<String>, io::Error> {
        if let Some(newline_offset) =
            buf[self.next_index..].iter().position(|b| *b == b'\n')
        {
            let newline_index = newline_offset + self.next_index;
            let line = buf.split_to(newline_index + 1);
            let line = &line[..line.len()-1];
            let line = without_carriage_return(line);
            let line = utf8(line)?;
            self.next_index = 0;
            Ok(Some(line.to_string()))
        } else {
            self.next_index = buf.len();
            Ok(None)
        }
    }

    fn decode_eof(&mut self, buf: &mut BytesMut) -> Result<Option<String>, io::Error> {
        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.take();
                    let line = without_carriage_return(&line);
                    let line = utf8(line)?;
                    self.next_index = 0;
                    Some(line.to_string())
                }
            }
        })
    }
}

impl Encoder for LinesCodec {
    type Item = String;
    type Error = io::Error;

    fn encode(&mut self, line: String, buf: &mut BytesMut) -> Result<(), io::Error> {
        buf.reserve(line.len() + 1);
        buf.put(line);
        buf.put_u8(b'\n');
        Ok(())
    }
}