use std::fmt;
#[cfg(any(
    feature = "gzip",
    feature = "zstd",
    feature = "brotli",
    feature = "deflate"
))]
use std::future::Future;
use std::pin::Pin;
use std::task::{Context, Poll, ready};

#[cfg(any(
    feature = "gzip",
    feature = "zstd",
    feature = "brotli",
    feature = "deflate"
))]
use futures_util::stream::Fuse;

#[cfg(feature = "gzip")]
use async_compression::tokio::bufread::GzipDecoder;

#[cfg(feature = "brotli")]
use async_compression::tokio::bufread::BrotliDecoder;

#[cfg(feature = "zstd")]
use async_compression::tokio::bufread::ZstdDecoder;

#[cfg(feature = "deflate")]
use async_compression::tokio::bufread::ZlibDecoder;

#[cfg(any(
    feature = "gzip",
    feature = "zstd",
    feature = "brotli",
    feature = "deflate",
))]
use futures_util::Stream;

use bytes::Bytes;
use http::HeaderMap;
use hyper2::body::Body as HttpBody;
use hyper2::body::Frame;

#[cfg(any(
    feature = "gzip",
    feature = "brotli",
    feature = "zstd",
    feature = "deflate"
))]
use tokio_util::codec::{BytesCodec, FramedRead};
#[cfg(any(
    feature = "gzip",
    feature = "brotli",
    feature = "zstd",
    feature = "deflate"
))]
use tokio_util::io::StreamReader;

use super::body::ResponseBody;

#[derive(Clone, Copy, Debug)]
pub(super) struct Accepts {
    #[cfg(feature = "gzip")]
    pub(super) gzip: bool,
    #[cfg(feature = "brotli")]
    pub(super) brotli: bool,
    #[cfg(feature = "zstd")]
    pub(super) zstd: bool,
    #[cfg(feature = "deflate")]
    pub(super) deflate: bool,
}

/// A response decompressor over a non-blocking stream of chunks.
///
/// The inner decoder may be constructed asynchronously.
pub(crate) struct Decoder {
    inner: Inner,
}

#[cfg(any(
    feature = "gzip",
    feature = "zstd",
    feature = "brotli",
    feature = "deflate"
))]
type PeekableIoStream = futures_util::stream::Peekable<IoStream>;

#[cfg(any(
    feature = "gzip",
    feature = "zstd",
    feature = "brotli",
    feature = "deflate"
))]
type PeekableIoStreamReader = StreamReader<PeekableIoStream, Bytes>;

#[allow(clippy::type_complexity)]
enum Inner {
    /// A `PlainText` decoder just returns the response content as is.
    PlainText(ResponseBody),

    /// A `Gzip` decoder will uncompress the gzipped response content before returning it.
    #[cfg(feature = "gzip")]
    Gzip(Pin<Box<Fuse<FramedRead<GzipDecoder<PeekableIoStreamReader>, BytesCodec>>>>),

    /// A `Brotli` decoder will uncompress the brotlied response content before returning it.
    #[cfg(feature = "brotli")]
    Brotli(Pin<Box<Fuse<FramedRead<BrotliDecoder<PeekableIoStreamReader>, BytesCodec>>>>),

    /// A `Zstd` decoder will uncompress the zstd compressed response content before returning it.
    #[cfg(feature = "zstd")]
    Zstd(Pin<Box<Fuse<FramedRead<ZstdDecoder<PeekableIoStreamReader>, BytesCodec>>>>),

    /// A `Deflate` decoder will uncompress the deflated response content before returning it.
    #[cfg(feature = "deflate")]
    Deflate(Pin<Box<Fuse<FramedRead<ZlibDecoder<PeekableIoStreamReader>, BytesCodec>>>>),

    /// A decoder that doesn't have a value yet.
    #[cfg(any(
        feature = "brotli",
        feature = "zstd",
        feature = "gzip",
        feature = "deflate"
    ))]
    Pending(Pin<Box<Pending>>),
}

#[cfg(any(
    feature = "gzip",
    feature = "zstd",
    feature = "brotli",
    feature = "deflate"
))]
/// A future attempt to poll the response body for EOF so we know whether to use gzip or not.
struct Pending(PeekableIoStream, DecoderType);

#[cfg(any(
    feature = "gzip",
    feature = "zstd",
    feature = "brotli",
    feature = "deflate",
))]
pub(crate) struct IoStream<B = ResponseBody>(B);

#[cfg(any(
    feature = "gzip",
    feature = "zstd",
    feature = "brotli",
    feature = "deflate"
))]
enum DecoderType {
    #[cfg(feature = "gzip")]
    Gzip,
    #[cfg(feature = "brotli")]
    Brotli,
    #[cfg(feature = "zstd")]
    Zstd,
    #[cfg(feature = "deflate")]
    Deflate,
}

impl fmt::Debug for Decoder {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.debug_struct("Decoder").finish()
    }
}

impl Decoder {
    /// A plain text decoder.
    ///
    /// This decoder will emit the underlying chunks as-is.
    fn plain_text(body: ResponseBody) -> Decoder {
        Decoder {
            inner: Inner::PlainText(body),
        }
    }

    /// A gzip decoder.
    ///
    /// This decoder will buffer and decompress chunks that are gzipped.
    #[cfg(feature = "gzip")]
    fn gzip(body: ResponseBody) -> Decoder {
        use futures_util::StreamExt;

        Decoder {
            inner: Inner::Pending(Box::pin(Pending(
                IoStream(body).peekable(),
                DecoderType::Gzip,
            ))),
        }
    }

    /// A brotli decoder.
    ///
    /// This decoder will buffer and decompress chunks that are brotlied.
    #[cfg(feature = "brotli")]
    fn brotli(body: ResponseBody) -> Decoder {
        use futures_util::StreamExt;

        Decoder {
            inner: Inner::Pending(Box::pin(Pending(
                IoStream(body).peekable(),
                DecoderType::Brotli,
            ))),
        }
    }

    /// A zstd decoder.
    ///
    /// This decoder will buffer and decompress chunks that are zstd compressed.
    #[cfg(feature = "zstd")]
    fn zstd(body: ResponseBody) -> Decoder {
        use futures_util::StreamExt;

        Decoder {
            inner: Inner::Pending(Box::pin(Pending(
                IoStream(body).peekable(),
                DecoderType::Zstd,
            ))),
        }
    }

    /// A deflate decoder.
    ///
    /// This decoder will buffer and decompress chunks that are deflated.
    #[cfg(feature = "deflate")]
    fn deflate(body: ResponseBody) -> Decoder {
        use futures_util::StreamExt;

        Decoder {
            inner: Inner::Pending(Box::pin(Pending(
                IoStream(body).peekable(),
                DecoderType::Deflate,
            ))),
        }
    }

    #[cfg(any(
        feature = "brotli",
        feature = "zstd",
        feature = "gzip",
        feature = "deflate"
    ))]
    fn detect_encoding(headers: &mut HeaderMap, encoding_str: &str) -> bool {
        use http::header::{CONTENT_ENCODING, CONTENT_LENGTH, TRANSFER_ENCODING};
        use log::warn;

        let mut is_content_encoded = {
            headers
                .get_all(CONTENT_ENCODING)
                .iter()
                .any(|enc| enc == encoding_str)
                || headers
                    .get_all(TRANSFER_ENCODING)
                    .iter()
                    .any(|enc| enc == encoding_str)
        };
        if is_content_encoded {
            if let Some(content_length) = headers.get(CONTENT_LENGTH) {
                if content_length == "0" {
                    warn!("{encoding_str} response with content-length of 0");
                    is_content_encoded = false;
                }
            }
        }
        if is_content_encoded {
            headers.remove(CONTENT_ENCODING);
            headers.remove(CONTENT_LENGTH);
        }
        is_content_encoded
    }

    /// Constructs a Decoder from a hyper request.
    ///
    /// A decoder is just a wrapper around the hyper request that knows
    /// how to decode the content body of the request.
    ///
    /// Uses the correct variant by inspecting the Content-Encoding header.
    pub(super) fn detect(
        _headers: &mut HeaderMap,
        body: ResponseBody,
        _accepts: Accepts,
    ) -> Decoder {
        #[cfg(feature = "gzip")]
        {
            if _accepts.gzip && Decoder::detect_encoding(_headers, "gzip") {
                return Decoder::gzip(body);
            }
        }

        #[cfg(feature = "brotli")]
        {
            if _accepts.brotli && Decoder::detect_encoding(_headers, "br") {
                return Decoder::brotli(body);
            }
        }

        #[cfg(feature = "zstd")]
        {
            if _accepts.zstd && Decoder::detect_encoding(_headers, "zstd") {
                return Decoder::zstd(body);
            }
        }

        #[cfg(feature = "deflate")]
        {
            if _accepts.deflate && Decoder::detect_encoding(_headers, "deflate") {
                return Decoder::deflate(body);
            }
        }

        Decoder::plain_text(body)
    }
}

impl HttpBody for Decoder {
    type Data = Bytes;
    type Error = crate::Error;

    fn poll_frame(
        mut self: Pin<&mut Self>,
        cx: &mut Context,
    ) -> Poll<Option<Result<Frame<Self::Data>, Self::Error>>> {
        match self.inner {
            #[cfg(any(
                feature = "brotli",
                feature = "zstd",
                feature = "gzip",
                feature = "deflate"
            ))]
            Inner::Pending(ref mut future) => match Pin::new(future).poll(cx) {
                Poll::Ready(Ok(inner)) => {
                    self.inner = inner;
                    self.poll_frame(cx)
                }
                Poll::Ready(Err(e)) => Poll::Ready(Some(Err(crate::error::decode_io(e)))),
                Poll::Pending => Poll::Pending,
            },
            Inner::PlainText(ref mut body) => match ready!(Pin::new(body).poll_frame(cx)) {
                Some(Ok(frame)) => Poll::Ready(Some(Ok(frame))),
                Some(Err(err)) => Poll::Ready(Some(Err(crate::error::decode(err)))),
                None => Poll::Ready(None),
            },
            #[cfg(feature = "gzip")]
            Inner::Gzip(ref mut decoder) => {
                match ready!(Pin::new(&mut *decoder).poll_next(cx)) {
                    Some(Ok(bytes)) => Poll::Ready(Some(Ok(Frame::data(bytes.freeze())))),
                    Some(Err(err)) => Poll::Ready(Some(Err(crate::error::decode_io(err)))),
                    None => {
                        // poll inner connection until EOF after gzip stream is finished
                        poll_inner_should_be_empty(
                            decoder.get_mut().get_mut().get_mut().get_mut(),
                            cx,
                        )
                    }
                }
            }
            #[cfg(feature = "brotli")]
            Inner::Brotli(ref mut decoder) => {
                match ready!(Pin::new(&mut *decoder).poll_next(cx)) {
                    Some(Ok(bytes)) => Poll::Ready(Some(Ok(Frame::data(bytes.freeze())))),
                    Some(Err(err)) => Poll::Ready(Some(Err(crate::error::decode_io(err)))),
                    None => {
                        // poll inner connection until EOF after brotli stream is finished
                        poll_inner_should_be_empty(
                            decoder.get_mut().get_mut().get_mut().get_mut(),
                            cx,
                        )
                    }
                }
            }
            #[cfg(feature = "zstd")]
            Inner::Zstd(ref mut decoder) => {
                match ready!(Pin::new(&mut *decoder).poll_next(cx)) {
                    Some(Ok(bytes)) => Poll::Ready(Some(Ok(Frame::data(bytes.freeze())))),
                    Some(Err(err)) => Poll::Ready(Some(Err(crate::error::decode_io(err)))),
                    None => {
                        // poll inner connection until EOF after zstd stream is finished
                        poll_inner_should_be_empty(
                            decoder.get_mut().get_mut().get_mut().get_mut(),
                            cx,
                        )
                    }
                }
            }
            #[cfg(feature = "deflate")]
            Inner::Deflate(ref mut decoder) => {
                match ready!(Pin::new(&mut *decoder).poll_next(cx)) {
                    Some(Ok(bytes)) => Poll::Ready(Some(Ok(Frame::data(bytes.freeze())))),
                    Some(Err(err)) => Poll::Ready(Some(Err(crate::error::decode_io(err)))),
                    None => {
                        // poll inner connection until EOF after deflate stream is finished
                        poll_inner_should_be_empty(
                            decoder.get_mut().get_mut().get_mut().get_mut(),
                            cx,
                        )
                    }
                }
            }
        }
    }

    fn size_hint(&self) -> http_body::SizeHint {
        match self.inner {
            Inner::PlainText(ref body) => HttpBody::size_hint(body),
            // the rest are "unknown", so default
            #[cfg(any(
                feature = "brotli",
                feature = "zstd",
                feature = "gzip",
                feature = "deflate"
            ))]
            _ => http_body::SizeHint::default(),
        }
    }
}

#[cfg(any(
    feature = "gzip",
    feature = "zstd",
    feature = "brotli",
    feature = "deflate"
))]
fn poll_inner_should_be_empty(
    inner: &mut PeekableIoStream,
    cx: &mut Context,
) -> Poll<Option<Result<Frame<Bytes>, crate::Error>>> {
    // poll inner connection until EOF after deflate stream is finished
    // loop in case of empty frames
    let mut inner = Pin::new(inner);
    loop {
        match ready!(inner.as_mut().poll_next(cx)) {
            // ignore any empty frames
            Some(Ok(bytes)) if bytes.is_empty() => continue,
            Some(Ok(_)) => {
                return Poll::Ready(Some(Err(crate::error::decode(
                    "there are extra bytes after body has been decompressed",
                ))));
            }
            Some(Err(err)) => return Poll::Ready(Some(Err(crate::error::decode_io(err)))),
            None => return Poll::Ready(None),
        }
    }
}

#[cfg(any(
    feature = "gzip",
    feature = "zstd",
    feature = "brotli",
    feature = "deflate",
))]
fn empty() -> ResponseBody {
    use http_body_util::{BodyExt, Empty, combinators::BoxBody};
    BoxBody::new(Empty::new().map_err(|never| match never {}))
}

#[cfg(any(
    feature = "gzip",
    feature = "zstd",
    feature = "brotli",
    feature = "deflate"
))]
impl Future for Pending {
    type Output = Result<Inner, std::io::Error>;

    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
        use futures_util::StreamExt;

        match ready!(Pin::new(&mut self.0).poll_peek(cx)) {
            Some(Ok(_)) => {
                // fallthrough
            }
            Some(Err(_e)) => {
                // error was just a ref, so we need to really poll to move it
                return Poll::Ready(Err(ready!(Pin::new(&mut self.0).poll_next(cx))
                    .expect("just peeked Some")
                    .unwrap_err()));
            }
            None => return Poll::Ready(Ok(Inner::PlainText(empty()))),
        };

        let _body = std::mem::replace(&mut self.0, IoStream(empty()).peekable());

        match self.1 {
            #[cfg(feature = "brotli")]
            DecoderType::Brotli => Poll::Ready(Ok(Inner::Brotli(Box::pin(
                FramedRead::new(
                    BrotliDecoder::new(StreamReader::new(_body)),
                    BytesCodec::new(),
                )
                .fuse(),
            )))),
            #[cfg(feature = "zstd")]
            DecoderType::Zstd => Poll::Ready(Ok(Inner::Zstd(Box::pin(
                FramedRead::new(
                    {
                        let mut d = ZstdDecoder::new(StreamReader::new(_body));
                        d.multiple_members(true);
                        d
                    },
                    BytesCodec::new(),
                )
                .fuse(),
            )))),
            #[cfg(feature = "gzip")]
            DecoderType::Gzip => Poll::Ready(Ok(Inner::Gzip(Box::pin(
                FramedRead::new(
                    GzipDecoder::new(StreamReader::new(_body)),
                    BytesCodec::new(),
                )
                .fuse(),
            )))),
            #[cfg(feature = "deflate")]
            DecoderType::Deflate => Poll::Ready(Ok(Inner::Deflate(Box::pin(
                FramedRead::new(
                    ZlibDecoder::new(StreamReader::new(_body)),
                    BytesCodec::new(),
                )
                .fuse(),
            )))),
        }
    }
}

#[cfg(any(
    feature = "gzip",
    feature = "zstd",
    feature = "brotli",
    feature = "deflate",
))]
impl<B> Stream for IoStream<B>
where
    B: HttpBody<Data = Bytes> + Unpin,
    B::Error: Into<Box<dyn std::error::Error + Send + Sync>>,
{
    type Item = Result<Bytes, std::io::Error>;

    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<Option<Self::Item>> {
        loop {
            return match ready!(Pin::new(&mut self.0).poll_frame(cx)) {
                Some(Ok(frame)) => {
                    // skip non-data frames
                    if let Ok(buf) = frame.into_data() {
                        Poll::Ready(Some(Ok(buf)))
                    } else {
                        continue;
                    }
                }
                Some(Err(err)) => Poll::Ready(Some(Err(crate::error::into_io(err.into())))),
                None => Poll::Ready(None),
            };
        }
    }
}

// ===== impl Accepts =====

impl Accepts {
    pub(super) fn none() -> Self {
        Accepts {
            #[cfg(feature = "gzip")]
            gzip: false,
            #[cfg(feature = "brotli")]
            brotli: false,
            #[cfg(feature = "zstd")]
            zstd: false,
            #[cfg(feature = "deflate")]
            deflate: false,
        }
    }
}

#[cfg(any(
    feature = "gzip",
    feature = "brotli",
    feature = "zstd",
    feature = "deflate",
    test
))]
impl Accepts {
    pub(super) const fn as_str(&self) -> Option<&'static str> {
        match (
            self.is_gzip(),
            self.is_brotli(),
            self.is_zstd(),
            self.is_deflate(),
        ) {
            (true, true, true, true) => Some("gzip, br, zstd, deflate"),
            (true, true, false, true) => Some("gzip, br, deflate"),
            (true, true, true, false) => Some("gzip, br, zstd"),
            (true, true, false, false) => Some("gzip, br"),
            (true, false, true, true) => Some("gzip, zstd, deflate"),
            (true, false, false, true) => Some("gzip, deflate"),
            (false, true, true, true) => Some("br, zstd, deflate"),
            (false, true, false, true) => Some("br, deflate"),
            (true, false, true, false) => Some("gzip, zstd"),
            (true, false, false, false) => Some("gzip"),
            (false, true, true, false) => Some("br, zstd"),
            (false, true, false, false) => Some("br"),
            (false, false, true, true) => Some("zstd, deflate"),
            (false, false, true, false) => Some("zstd"),
            (false, false, false, true) => Some("deflate"),
            (false, false, false, false) => None,
        }
    }

    const fn is_gzip(&self) -> bool {
        #[cfg(feature = "gzip")]
        {
            self.gzip
        }

        #[cfg(not(feature = "gzip"))]
        {
            false
        }
    }

    const fn is_brotli(&self) -> bool {
        #[cfg(feature = "brotli")]
        {
            self.brotli
        }

        #[cfg(not(feature = "brotli"))]
        {
            false
        }
    }

    const fn is_zstd(&self) -> bool {
        #[cfg(feature = "zstd")]
        {
            self.zstd
        }

        #[cfg(not(feature = "zstd"))]
        {
            false
        }
    }

    const fn is_deflate(&self) -> bool {
        #[cfg(feature = "deflate")]
        {
            self.deflate
        }

        #[cfg(not(feature = "deflate"))]
        {
            false
        }
    }
}

#[allow(clippy::all)]
impl Default for Accepts {
    fn default() -> Accepts {
        Accepts {
            #[cfg(feature = "gzip")]
            gzip: true,
            #[cfg(feature = "brotli")]
            brotli: true,
            #[cfg(feature = "zstd")]
            zstd: true,
            #[cfg(feature = "deflate")]
            deflate: true,
        }
    }
}

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

    #[test]
    fn accepts_as_str() {
        fn format_accept_encoding(accepts: &Accepts) -> String {
            let mut encodings = vec![];
            if accepts.is_gzip() {
                encodings.push("gzip");
            }
            if accepts.is_brotli() {
                encodings.push("br");
            }
            if accepts.is_zstd() {
                encodings.push("zstd");
            }
            if accepts.is_deflate() {
                encodings.push("deflate");
            }
            encodings.join(", ")
        }

        let state = [true, false];
        let mut permutations = Vec::new();

        #[allow(unused_variables)]
        for gzip in state {
            for brotli in state {
                for zstd in state {
                    for deflate in state {
                        permutations.push(Accepts {
                            #[cfg(feature = "gzip")]
                            gzip,
                            #[cfg(feature = "brotli")]
                            brotli,
                            #[cfg(feature = "zstd")]
                            zstd,
                            #[cfg(feature = "deflate")]
                            deflate,
                        });
                    }
                }
            }
        }

        for accepts in permutations {
            let expected = format_accept_encoding(&accepts);
            let got = accepts.as_str().unwrap_or("");
            assert_eq!(got, expected.as_str());
        }
    }
}
