use std::{
    ops::{Deref, DerefMut},
    pin::Pin,
    task::{ready, Context, Poll},
};

use base64::{prelude::BASE64_STANDARD, Engine};
use byteorder::{BigEndian, ByteOrder};
use bytes::{BufMut, Bytes, BytesMut};
use http::{header::HeaderName, HeaderMap, HeaderValue};
use http_body::Body;
use httparse::{Status, EMPTY_HEADER};
use pin_project::pin_project;
use wasm_bindgen::JsCast;
use web_sys::ReadableStream;

use crate::{body_stream::BodyStream, content_type::Encoding, Error};

/// If 8th MSB of a frame is `0` for data and `1` for trailer
const TRAILER_BIT: u8 = 0b10000000;

pub struct EncodedBytes {
    encoding: Encoding,
    raw_buf: BytesMut,
    buf: BytesMut,
}

impl EncodedBytes {
    pub fn new(content_type: &str) -> Result<Self, Error> {
        Ok(Self {
            encoding: Encoding::from_content_type(content_type)?,
            raw_buf: BytesMut::new(),
            buf: BytesMut::new(),
        })
    }

    // This is to avoid passing a slice of bytes with a length that the base64
    // decoder would consider invalid.
    #[inline]
    fn max_decodable(&self) -> usize {
        (self.raw_buf.len() / 4) * 4
    }

    fn decode_base64_chunk(&mut self) -> Result<(), Error> {
        let index = self.max_decodable();

        if self.raw_buf.len() >= index {
            let decoded = BASE64_STANDARD
                .decode(self.buf.split_to(index))
                .map(Bytes::from)?;
            self.buf.put(decoded);
        }

        Ok(())
    }

    fn append(&mut self, bytes: Bytes) -> Result<(), Error> {
        match self.encoding {
            Encoding::None => self.buf.put(bytes),
            Encoding::Base64 => {
                self.raw_buf.put(bytes);
                self.decode_base64_chunk()?;
            }
        }

        Ok(())
    }

    fn take(&mut self, length: usize) -> BytesMut {
        let new_buf = self.buf.split_off(length);
        std::mem::replace(&mut self.buf, new_buf)
    }
}

impl Deref for EncodedBytes {
    type Target = BytesMut;

    fn deref(&self) -> &Self::Target {
        &self.buf
    }
}

impl DerefMut for EncodedBytes {
    fn deref_mut(&mut self) -> &mut Self::Target {
        &mut self.buf
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum ReadState {
    CompressionFlag,
    DataLength,
    Data(u32),
    TrailerLength,
    Trailer(u32),
    Done,
}

impl ReadState {
    fn finished_data(&self) -> bool {
        matches!(self, ReadState::TrailerLength)
            || matches!(self, ReadState::Trailer(_))
            || matches!(self, ReadState::Done)
    }
}

/// Type to handle HTTP response
#[pin_project]
pub struct ResponseBody {
    #[pin]
    body_stream: BodyStream,
    buf: EncodedBytes,
    incomplete_data: BytesMut,
    data: Option<BytesMut>,
    trailer: Option<HeaderMap>,
    state: ReadState,
    finished_stream: bool,
}

impl ResponseBody {
    pub(crate) fn new(body_stream: ReadableStream, content_type: &str) -> Result<Self, Error> {
        let body_stream =
            wasm_streams::ReadableStream::from_raw(body_stream.unchecked_into()).into_stream();

        Ok(Self {
            body_stream: BodyStream::new(body_stream),
            buf: EncodedBytes::new(content_type)?,
            incomplete_data: BytesMut::new(),
            data: None,
            trailer: None,
            state: ReadState::CompressionFlag,
            finished_stream: false,
        })
    }

    fn read_stream(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Error>> {
        if self.finished_stream {
            return Poll::Ready(Ok(()));
        }

        let this = self.project();

        match ready!(this.body_stream.poll_frame(cx)) {
            Some(Ok(frame)) => {
                if let Some(data) = frame.data_ref() {
                    if let Err(e) = this.buf.append(data.clone()) {
                        return Poll::Ready(Err(e));
                    }
                };

                Poll::Ready(Ok(()))
            }
            Some(Err(e)) => Poll::Ready(Err(e)),
            None => {
                *this.finished_stream = true;
                Poll::Ready(Ok(()))
            }
        }
    }

    fn step(self: Pin<&mut Self>) -> Result<(), Error> {
        let this = self.project();

        loop {
            match this.state {
                ReadState::CompressionFlag => {
                    if this.buf.is_empty() {
                        // Can't read compression flag right now
                        return Ok(());
                    } else {
                        let compression_flag = this.buf.take(1);

                        if compression_flag[0] & TRAILER_BIT == 0 {
                            this.incomplete_data.unsplit(compression_flag);
                            *this.state = ReadState::DataLength;
                        } else {
                            *this.state = ReadState::TrailerLength;
                        }
                    }
                }
                ReadState::DataLength => {
                    if this.buf.len() < 4 {
                        // Can't read data length right now
                        return Ok(());
                    } else {
                        let data_length_bytes = this.buf.take(4);
                        let data_length = BigEndian::read_u32(data_length_bytes.as_ref());

                        this.incomplete_data.unsplit(data_length_bytes);
                        *this.state = ReadState::Data(data_length);
                    }
                }
                ReadState::Data(data_length) => {
                    let data_length = *data_length as usize;

                    if this.buf.len() < data_length {
                        // Can't read data right now
                        return Ok(());
                    } else {
                        this.incomplete_data.unsplit(this.buf.take(data_length));

                        let new_data = this.incomplete_data.split();

                        if let Some(data) = this.data {
                            data.unsplit(new_data);
                        } else {
                            *this.data = Some(new_data);
                        }

                        *this.state = ReadState::CompressionFlag;
                    }
                }
                ReadState::TrailerLength => {
                    if this.buf.len() < 4 {
                        // Can't read data length right now
                        return Ok(());
                    } else {
                        let trailer_length_bytes = this.buf.take(4);
                        let trailer_length = BigEndian::read_u32(trailer_length_bytes.as_ref());
                        *this.state = ReadState::Trailer(trailer_length);
                    }
                }
                ReadState::Trailer(trailer_length) => {
                    let trailer_length = *trailer_length as usize;

                    if this.buf.len() < trailer_length {
                        // Can't read trailer right now
                        return Ok(());
                    } else {
                        let mut trailer_bytes = this.buf.take(trailer_length);
                        trailer_bytes.put_u8(b'\n');

                        let mut trailers_buf = [EMPTY_HEADER; 64];
                        let parsed_trailers =
                            match httparse::parse_headers(&trailer_bytes, &mut trailers_buf)
                                .map_err(|_| Error::HeaderParsingError)?
                            {
                                Status::Complete((_, headers)) => Ok(headers),
                                Status::Partial => Err(Error::HeaderParsingError),
                            }?;

                        let mut trailers = HeaderMap::with_capacity(parsed_trailers.len());

                        for parsed_trailer in parsed_trailers {
                            let header_name =
                                HeaderName::from_bytes(parsed_trailer.name.as_bytes())?;
                            let header_value = HeaderValue::from_bytes(parsed_trailer.value)?;
                            trailers.insert(header_name, header_value);
                        }

                        *this.trailer = Some(trailers);

                        *this.state = ReadState::Done;
                    }
                }
                ReadState::Done => return Ok(()),
            }
        }
    }
}

impl Body for ResponseBody {
    type Data = Bytes;

    type Error = Error;

    fn poll_frame(
        mut self: Pin<&mut Self>,
        cx: &mut Context<'_>,
    ) -> Poll<Option<Result<http_body::Frame<Self::Data>, Self::Error>>> {
        // Check if there's already some data in buffer and return that
        if self.data.is_some() {
            let data = self.data.take().unwrap();

            return Poll::Ready(Some(Ok(http_body::Frame::data(data.freeze()))));
        }

        // If reading data is finished return `None`
        if self.state.finished_data() {
            return Poll::Ready(None);
        }

        loop {
            // Read bytes from stream
            if let Err(e) = ready!(self.as_mut().read_stream(cx)) {
                return Poll::Ready(Some(Err(e)));
            }

            // Step the state machine
            if let Err(e) = self.as_mut().step() {
                return Poll::Ready(Some(Err(e)));
            }

            if self.data.is_some() {
                // If data is available in buffer, return that
                let data = self.data.take().unwrap();
                return Poll::Ready(Some(Ok(http_body::Frame::data(data.freeze()))));
            } else if self.state.finished_data() {
                // If we finished reading data continue return `None`
                return Poll::Ready(None);
            } else if self.finished_stream {
                // If stream is finished but data is not finished return error
                return Poll::Ready(Some(Err(Error::MalformedResponse)));
            }
        }
    }
}

impl Default for ResponseBody {
    fn default() -> Self {
        Self {
            body_stream: BodyStream::empty(),
            buf: EncodedBytes {
                encoding: Encoding::None,
                raw_buf: BytesMut::new(),
                buf: BytesMut::new(),
            },
            incomplete_data: BytesMut::new(),
            data: None,
            trailer: None,
            state: ReadState::Done,
            finished_stream: true,
        }
    }
}