use std::error::Error as StdError;
use std::fmt;
use std::io;
use std::usize;

use bytes::Bytes;

use crate::common::{task, Poll};

use super::io::MemRead;
use super::DecodedLength;

use self::Kind::{Chunked, Eof, Length};

/// Decoders to handle different Transfer-Encodings.
///
/// If a message body does not include a Transfer-Encoding, it *should*
/// include a Content-Length header.
#[derive(Clone, PartialEq)]
pub struct Decoder {
    kind: Kind,
}

#[derive(Debug, Clone, Copy, PartialEq)]
enum Kind {
    /// A Reader used when a Content-Length header is passed with a positive integer.
    Length(u64),
    /// A Reader used when Transfer-Encoding is `chunked`.
    Chunked(ChunkedState, u64),
    /// A Reader used for responses that don't indicate a length or chunked.
    ///
    /// The bool tracks when EOF is seen on the transport.
    ///
    /// Note: This should only used for `Response`s. It is illegal for a
    /// `Request` to be made with both `Content-Length` and
    /// `Transfer-Encoding: chunked` missing, as explained from the spec:
    ///
    /// > If a Transfer-Encoding header field is present in a response and
    /// > the chunked transfer coding is not the final encoding, the
    /// > message body length is determined by reading the connection until
    /// > it is closed by the server.  If a Transfer-Encoding header field
    /// > is present in a request and the chunked transfer coding is not
    /// > the final encoding, the message body length cannot be determined
    /// > reliably; the server MUST respond with the 400 (Bad Request)
    /// > status code and then close the connection.
    Eof(bool),
}

#[derive(Debug, PartialEq, Clone, Copy)]
enum ChunkedState {
    Size,
    SizeLws,
    Extension,
    SizeLf,
    Body,
    BodyCr,
    BodyLf,
    EndCr,
    EndLf,
    End,
}

impl Decoder {
    // constructors

    pub fn length(x: u64) -> Decoder {
        Decoder {
            kind: Kind::Length(x),
        }
    }

    pub fn chunked() -> Decoder {
        Decoder {
            kind: Kind::Chunked(ChunkedState::Size, 0),
        }
    }

    pub fn eof() -> Decoder {
        Decoder {
            kind: Kind::Eof(false),
        }
    }

    pub(super) fn new(len: DecodedLength) -> Self {
        match len {
            DecodedLength::CHUNKED => Decoder::chunked(),
            DecodedLength::CLOSE_DELIMITED => Decoder::eof(),
            length => Decoder::length(length.danger_len()),
        }
    }

    // methods

    pub fn is_eof(&self) -> bool {
        match self.kind {
            Length(0) | Chunked(ChunkedState::End, _) | Eof(true) => true,
            _ => false,
        }
    }

    pub fn decode<R: MemRead>(
        &mut self,
        cx: &mut task::Context<'_>,
        body: &mut R,
    ) -> Poll<Result<Bytes, io::Error>> {
        trace!("decode; state={:?}", self.kind);
        match self.kind {
            Length(ref mut remaining) => {
                if *remaining == 0 {
                    Poll::Ready(Ok(Bytes::new()))
                } else {
                    let to_read = *remaining as usize;
                    let buf = ready!(body.read_mem(cx, to_read))?;
                    let num = buf.as_ref().len() as u64;
                    if num > *remaining {
                        *remaining = 0;
                    } else if num == 0 {
                        return Poll::Ready(Err(io::Error::new(
                            io::ErrorKind::UnexpectedEof,
                            IncompleteBody,
                        )));
                    } else {
                        *remaining -= num;
                    }
                    Poll::Ready(Ok(buf))
                }
            }
            Chunked(ref mut state, ref mut size) => {
                loop {
                    let mut buf = None;
                    // advances the chunked state
                    *state = ready!(state.step(cx, body, size, &mut buf))?;
                    if *state == ChunkedState::End {
                        trace!("end of chunked");
                        return Poll::Ready(Ok(Bytes::new()));
                    }
                    if let Some(buf) = buf {
                        return Poll::Ready(Ok(buf));
                    }
                }
            }
            Eof(ref mut is_eof) => {
                if *is_eof {
                    Poll::Ready(Ok(Bytes::new()))
                } else {
                    // 8192 chosen because its about 2 packets, there probably
                    // won't be that much available, so don't have MemReaders
                    // allocate buffers to big
                    body.read_mem(cx, 8192).map_ok(|slice| {
                        *is_eof = slice.is_empty();
                        slice
                    })
                }
            }
        }
    }

    #[cfg(test)]
    async fn decode_fut<R: MemRead>(&mut self, body: &mut R) -> Result<Bytes, io::Error> {
        futures_util::future::poll_fn(move |cx| self.decode(cx, body)).await
    }
}

impl fmt::Debug for Decoder {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        fmt::Debug::fmt(&self.kind, f)
    }
}

macro_rules! byte (
    ($rdr:ident, $cx:expr) => ({
        let buf = ready!($rdr.read_mem($cx, 1))?;
        if !buf.is_empty() {
            buf[0]
        } else {
            return Poll::Ready(Err(io::Error::new(io::ErrorKind::UnexpectedEof,
                                      "unexpected EOF during chunk size line")));
        }
    })
);

impl ChunkedState {
    fn step<R: MemRead>(
        &self,
        cx: &mut task::Context<'_>,
        body: &mut R,
        size: &mut u64,
        buf: &mut Option<Bytes>,
    ) -> Poll<Result<ChunkedState, io::Error>> {
        use self::ChunkedState::*;
        match *self {
            Size => ChunkedState::read_size(cx, body, size),
            SizeLws => ChunkedState::read_size_lws(cx, body),
            Extension => ChunkedState::read_extension(cx, body),
            SizeLf => ChunkedState::read_size_lf(cx, body, *size),
            Body => ChunkedState::read_body(cx, body, size, buf),
            BodyCr => ChunkedState::read_body_cr(cx, body),
            BodyLf => ChunkedState::read_body_lf(cx, body),
            EndCr => ChunkedState::read_end_cr(cx, body),
            EndLf => ChunkedState::read_end_lf(cx, body),
            End => Poll::Ready(Ok(ChunkedState::End)),
        }
    }
    fn read_size<R: MemRead>(
        cx: &mut task::Context<'_>,
        rdr: &mut R,
        size: &mut u64,
    ) -> Poll<Result<ChunkedState, io::Error>> {
        trace!("Read chunk hex size");
        let radix = 16;
        match byte!(rdr, cx) {
            b @ b'0'..=b'9' => {
                *size *= radix;
                *size += (b - b'0') as u64;
            }
            b @ b'a'..=b'f' => {
                *size *= radix;
                *size += (b + 10 - b'a') as u64;
            }
            b @ b'A'..=b'F' => {
                *size *= radix;
                *size += (b + 10 - b'A') as u64;
            }
            b'\t' | b' ' => return Poll::Ready(Ok(ChunkedState::SizeLws)),
            b';' => return Poll::Ready(Ok(ChunkedState::Extension)),
            b'\r' => return Poll::Ready(Ok(ChunkedState::SizeLf)),
            _ => {
                return Poll::Ready(Err(io::Error::new(
                    io::ErrorKind::InvalidInput,
                    "Invalid chunk size line: Invalid Size",
                )));
            }
        }
        Poll::Ready(Ok(ChunkedState::Size))
    }
    fn read_size_lws<R: MemRead>(
        cx: &mut task::Context<'_>,
        rdr: &mut R,
    ) -> Poll<Result<ChunkedState, io::Error>> {
        trace!("read_size_lws");
        match byte!(rdr, cx) {
            // LWS can follow the chunk size, but no more digits can come
            b'\t' | b' ' => Poll::Ready(Ok(ChunkedState::SizeLws)),
            b';' => Poll::Ready(Ok(ChunkedState::Extension)),
            b'\r' => Poll::Ready(Ok(ChunkedState::SizeLf)),
            _ => Poll::Ready(Err(io::Error::new(
                io::ErrorKind::InvalidInput,
                "Invalid chunk size linear white space",
            ))),
        }
    }
    fn read_extension<R: MemRead>(
        cx: &mut task::Context<'_>,
        rdr: &mut R,
    ) -> Poll<Result<ChunkedState, io::Error>> {
        trace!("read_extension");
        match byte!(rdr, cx) {
            b'\r' => Poll::Ready(Ok(ChunkedState::SizeLf)),
            _ => Poll::Ready(Ok(ChunkedState::Extension)), // no supported extensions
        }
    }
    fn read_size_lf<R: MemRead>(
        cx: &mut task::Context<'_>,
        rdr: &mut R,
        size: u64,
    ) -> Poll<Result<ChunkedState, io::Error>> {
        trace!("Chunk size is {:?}", size);
        match byte!(rdr, cx) {
            b'\n' => {
                if size == 0 {
                    Poll::Ready(Ok(ChunkedState::EndCr))
                } else {
                    debug!("incoming chunked header: {0:#X} ({0} bytes)", size);
                    Poll::Ready(Ok(ChunkedState::Body))
                }
            }
            _ => Poll::Ready(Err(io::Error::new(
                io::ErrorKind::InvalidInput,
                "Invalid chunk size LF",
            ))),
        }
    }

    fn read_body<R: MemRead>(
        cx: &mut task::Context<'_>,
        rdr: &mut R,
        rem: &mut u64,
        buf: &mut Option<Bytes>,
    ) -> Poll<Result<ChunkedState, io::Error>> {
        trace!("Chunked read, remaining={:?}", rem);

        // cap remaining bytes at the max capacity of usize
        let rem_cap = match *rem {
            r if r > usize::MAX as u64 => usize::MAX,
            r => r as usize,
        };

        let to_read = rem_cap;
        let slice = ready!(rdr.read_mem(cx, to_read))?;
        let count = slice.len();

        if count == 0 {
            *rem = 0;
            return Poll::Ready(Err(io::Error::new(
                io::ErrorKind::UnexpectedEof,
                IncompleteBody,
            )));
        }
        *buf = Some(slice);
        *rem -= count as u64;

        if *rem > 0 {
            Poll::Ready(Ok(ChunkedState::Body))
        } else {
            Poll::Ready(Ok(ChunkedState::BodyCr))
        }
    }
    fn read_body_cr<R: MemRead>(
        cx: &mut task::Context<'_>,
        rdr: &mut R,
    ) -> Poll<Result<ChunkedState, io::Error>> {
        match byte!(rdr, cx) {
            b'\r' => Poll::Ready(Ok(ChunkedState::BodyLf)),
            _ => Poll::Ready(Err(io::Error::new(
                io::ErrorKind::InvalidInput,
                "Invalid chunk body CR",
            ))),
        }
    }
    fn read_body_lf<R: MemRead>(
        cx: &mut task::Context<'_>,
        rdr: &mut R,
    ) -> Poll<Result<ChunkedState, io::Error>> {
        match byte!(rdr, cx) {
            b'\n' => Poll::Ready(Ok(ChunkedState::Size)),
            _ => Poll::Ready(Err(io::Error::new(
                io::ErrorKind::InvalidInput,
                "Invalid chunk body LF",
            ))),
        }
    }

    fn read_end_cr<R: MemRead>(
        cx: &mut task::Context<'_>,
        rdr: &mut R,
    ) -> Poll<Result<ChunkedState, io::Error>> {
        match byte!(rdr, cx) {
            b'\r' => Poll::Ready(Ok(ChunkedState::EndLf)),
            _ => Poll::Ready(Err(io::Error::new(
                io::ErrorKind::InvalidInput,
                "Invalid chunk end CR",
            ))),
        }
    }
    fn read_end_lf<R: MemRead>(
        cx: &mut task::Context<'_>,
        rdr: &mut R,
    ) -> Poll<Result<ChunkedState, io::Error>> {
        match byte!(rdr, cx) {
            b'\n' => Poll::Ready(Ok(ChunkedState::End)),
            _ => Poll::Ready(Err(io::Error::new(
                io::ErrorKind::InvalidInput,
                "Invalid chunk end LF",
            ))),
        }
    }
}

#[derive(Debug)]
struct IncompleteBody;

impl fmt::Display for IncompleteBody {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "end of file before message length reached")
    }
}

impl StdError for IncompleteBody {}

#[cfg(test)]
mod tests {
    use super::*;
    use std::pin::Pin;
    use std::time::Duration;
    use tokio::io::AsyncRead;

    impl<'a> MemRead for &'a [u8] {
        fn read_mem(&mut self, _: &mut task::Context<'_>, len: usize) -> Poll<io::Result<Bytes>> {
            let n = std::cmp::min(len, self.len());
            if n > 0 {
                let (a, b) = self.split_at(n);
                let buf = Bytes::copy_from_slice(a);
                *self = b;
                Poll::Ready(Ok(buf))
            } else {
                Poll::Ready(Ok(Bytes::new()))
            }
        }
    }

    impl<'a> MemRead for &'a mut (dyn AsyncRead + Unpin) {
        fn read_mem(&mut self, cx: &mut task::Context<'_>, len: usize) -> Poll<io::Result<Bytes>> {
            let mut v = vec![0; len];
            let n = ready!(Pin::new(self).poll_read(cx, &mut v)?);
            Poll::Ready(Ok(Bytes::copy_from_slice(&v[..n])))
        }
    }

    #[cfg(feature = "nightly")]
    impl MemRead for Bytes {
        fn read_mem(&mut self, _: &mut task::Context<'_>, len: usize) -> Poll<io::Result<Bytes>> {
            let n = std::cmp::min(len, self.len());
            let ret = self.split_to(n);
            Poll::Ready(Ok(ret))
        }
    }

    /*
    use std::io;
    use std::io::Write;
    use super::Decoder;
    use super::ChunkedState;
    use futures::{Async, Poll};
    use bytes::{BytesMut, Bytes};
    use crate::mock::AsyncIo;
    */

    #[tokio::test]
    async fn test_read_chunk_size() {
        use std::io::ErrorKind::{InvalidInput, UnexpectedEof};

        async fn read(s: &str) -> u64 {
            let mut state = ChunkedState::Size;
            let rdr = &mut s.as_bytes();
            let mut size = 0;
            loop {
                let result =
                    futures_util::future::poll_fn(|cx| state.step(cx, rdr, &mut size, &mut None))
                        .await;
                let desc = format!("read_size failed for {:?}", s);
                state = result.expect(desc.as_str());
                if state == ChunkedState::Body || state == ChunkedState::EndCr {
                    break;
                }
            }
            size
        }

        async fn read_err(s: &str, expected_err: io::ErrorKind) {
            let mut state = ChunkedState::Size;
            let rdr = &mut s.as_bytes();
            let mut size = 0;
            loop {
                let result =
                    futures_util::future::poll_fn(|cx| state.step(cx, rdr, &mut size, &mut None))
                        .await;
                state = match result {
                    Ok(s) => s,
                    Err(e) => {
                        assert!(
                            expected_err == e.kind(),
                            "Reading {:?}, expected {:?}, but got {:?}",
                            s,
                            expected_err,
                            e.kind()
                        );
                        return;
                    }
                };
                if state == ChunkedState::Body || state == ChunkedState::End {
                    panic!(format!("Was Ok. Expected Err for {:?}", s));
                }
            }
        }

        assert_eq!(1, read("1\r\n").await);
        assert_eq!(1, read("01\r\n").await);
        assert_eq!(0, read("0\r\n").await);
        assert_eq!(0, read("00\r\n").await);
        assert_eq!(10, read("A\r\n").await);
        assert_eq!(10, read("a\r\n").await);
        assert_eq!(255, read("Ff\r\n").await);
        assert_eq!(255, read("Ff   \r\n").await);
        // Missing LF or CRLF
        read_err("F\rF", InvalidInput).await;
        read_err("F", UnexpectedEof).await;
        // Invalid hex digit
        read_err("X\r\n", InvalidInput).await;
        read_err("1X\r\n", InvalidInput).await;
        read_err("-\r\n", InvalidInput).await;
        read_err("-1\r\n", InvalidInput).await;
        // Acceptable (if not fully valid) extensions do not influence the size
        assert_eq!(1, read("1;extension\r\n").await);
        assert_eq!(10, read("a;ext name=value\r\n").await);
        assert_eq!(1, read("1;extension;extension2\r\n").await);
        assert_eq!(1, read("1;;;  ;\r\n").await);
        assert_eq!(2, read("2; extension...\r\n").await);
        assert_eq!(3, read("3   ; extension=123\r\n").await);
        assert_eq!(3, read("3   ;\r\n").await);
        assert_eq!(3, read("3   ;   \r\n").await);
        // Invalid extensions cause an error
        read_err("1 invalid extension\r\n", InvalidInput).await;
        read_err("1 A\r\n", InvalidInput).await;
        read_err("1;no CRLF", UnexpectedEof).await;
    }

    #[tokio::test]
    async fn test_read_sized_early_eof() {
        let mut bytes = &b"foo bar"[..];
        let mut decoder = Decoder::length(10);
        assert_eq!(decoder.decode_fut(&mut bytes).await.unwrap().len(), 7);
        let e = decoder.decode_fut(&mut bytes).await.unwrap_err();
        assert_eq!(e.kind(), io::ErrorKind::UnexpectedEof);
    }

    #[tokio::test]
    async fn test_read_chunked_early_eof() {
        let mut bytes = &b"\
            9\r\n\
            foo bar\
        "[..];
        let mut decoder = Decoder::chunked();
        assert_eq!(decoder.decode_fut(&mut bytes).await.unwrap().len(), 7);
        let e = decoder.decode_fut(&mut bytes).await.unwrap_err();
        assert_eq!(e.kind(), io::ErrorKind::UnexpectedEof);
    }

    #[tokio::test]
    async fn test_read_chunked_single_read() {
        let mut mock_buf = &b"10\r\n1234567890abcdef\r\n0\r\n"[..];
        let buf = Decoder::chunked()
            .decode_fut(&mut mock_buf)
            .await
            .expect("decode");
        assert_eq!(16, buf.len());
        let result = String::from_utf8(buf.as_ref().to_vec()).expect("decode String");
        assert_eq!("1234567890abcdef", &result);
    }

    #[tokio::test]
    async fn test_read_chunked_after_eof() {
        let mut mock_buf = &b"10\r\n1234567890abcdef\r\n0\r\n\r\n"[..];
        let mut decoder = Decoder::chunked();

        // normal read
        let buf = decoder.decode_fut(&mut mock_buf).await.unwrap();
        assert_eq!(16, buf.len());
        let result = String::from_utf8(buf.as_ref().to_vec()).expect("decode String");
        assert_eq!("1234567890abcdef", &result);

        // eof read
        let buf = decoder.decode_fut(&mut mock_buf).await.expect("decode");
        assert_eq!(0, buf.len());

        // ensure read after eof also returns eof
        let buf = decoder.decode_fut(&mut mock_buf).await.expect("decode");
        assert_eq!(0, buf.len());
    }

    // perform an async read using a custom buffer size and causing a blocking
    // read at the specified byte
    async fn read_async(mut decoder: Decoder, content: &[u8], block_at: usize) -> String {
        let mut outs = Vec::new();

        let mut ins = if block_at == 0 {
            tokio_test::io::Builder::new()
                .wait(Duration::from_millis(10))
                .read(content)
                .build()
        } else {
            tokio_test::io::Builder::new()
                .read(&content[..block_at])
                .wait(Duration::from_millis(10))
                .read(&content[block_at..])
                .build()
        };

        let mut ins = &mut ins as &mut (dyn AsyncRead + Unpin);

        loop {
            let buf = decoder
                .decode_fut(&mut ins)
                .await
                .expect("unexpected decode error");
            if buf.is_empty() {
                break; // eof
            }
            outs.extend(buf.as_ref());
        }

        String::from_utf8(outs).expect("decode String")
    }

    // iterate over the different ways that this async read could go.
    // tests blocking a read at each byte along the content - The shotgun approach
    async fn all_async_cases(content: &str, expected: &str, decoder: Decoder) {
        let content_len = content.len();
        for block_at in 0..content_len {
            let actual = read_async(decoder.clone(), content.as_bytes(), block_at).await;
            assert_eq!(expected, &actual) //, "Failed async. Blocking at {}", block_at);
        }
    }

    #[tokio::test]
    async fn test_read_length_async() {
        let content = "foobar";
        all_async_cases(content, content, Decoder::length(content.len() as u64)).await;
    }

    #[tokio::test]
    async fn test_read_chunked_async() {
        let content = "3\r\nfoo\r\n3\r\nbar\r\n0\r\n\r\n";
        let expected = "foobar";
        all_async_cases(content, expected, Decoder::chunked()).await;
    }

    #[tokio::test]
    async fn test_read_eof_async() {
        let content = "foobar";
        all_async_cases(content, content, Decoder::eof()).await;
    }

    #[cfg(feature = "nightly")]
    #[bench]
    fn bench_decode_chunked_1kb(b: &mut test::Bencher) {
        let mut rt = new_runtime();

        const LEN: usize = 1024;
        let mut vec = Vec::new();
        vec.extend(format!("{:x}\r\n", LEN).as_bytes());
        vec.extend(&[0; LEN][..]);
        vec.extend(b"\r\n");
        let content = Bytes::from(vec);

        b.bytes = LEN as u64;

        b.iter(|| {
            let mut decoder = Decoder::chunked();
            rt.block_on(async {
                let mut raw = content.clone();
                let chunk = decoder.decode_fut(&mut raw).await.unwrap();
                assert_eq!(chunk.len(), LEN);
            });
        });
    }

    #[cfg(feature = "nightly")]
    #[bench]
    fn bench_decode_length_1kb(b: &mut test::Bencher) {
        let mut rt = new_runtime();

        const LEN: usize = 1024;
        let content = Bytes::from(&[0; LEN][..]);
        b.bytes = LEN as u64;

        b.iter(|| {
            let mut decoder = Decoder::length(LEN as u64);
            rt.block_on(async {
                let mut raw = content.clone();
                let chunk = decoder.decode_fut(&mut raw).await.unwrap();
                assert_eq!(chunk.len(), LEN);
            });
        });
    }

    #[cfg(feature = "nightly")]
    fn new_runtime() -> tokio::runtime::Runtime {
        tokio::runtime::Builder::new()
            .enable_all()
            .basic_scheduler()
            .build()
            .expect("rt build")
    }
}