use std::{
    io,
    io::{Read, Write},
    sync::mpsc::{sync_channel, Receiver, SyncSender, TrySendError},
    thread,
    time::Duration,
};

use curl::easy::Easy2;
use git_features::io::pipe;

use crate::client::blocking_io::http;

#[derive(Default)]
struct Handler {
    send_header: Option<pipe::Writer>,
    send_data: Option<pipe::Writer>,
    receive_body: Option<pipe::Reader>,
    checked_status: bool,
}

impl Handler {
    fn reset(&mut self) {
        self.checked_status = false;
    }
    fn parse_status_inner(data: &[u8]) -> Result<usize, Box<dyn std::error::Error + Send + Sync>> {
        let code = data
            .split(|b| *b == b' ')
            .nth(1)
            .ok_or("Expected HTTP/<VERSION> STATUS")?;
        let code = std::str::from_utf8(code)?;
        code.parse().map_err(Into::into)
    }
    fn parse_status(data: &[u8]) -> Option<(usize, Box<dyn std::error::Error + Send + Sync>)> {
        match Self::parse_status_inner(data) {
            Ok(status) if !(200..=299).contains(&status) => {
                Some((status, format!("Received HTTP status {}", status).into()))
            }
            Ok(_) => None,
            Err(err) => Some((500, err)),
        }
    }
}

impl curl::easy::Handler for Handler {
    fn write(&mut self, data: &[u8]) -> Result<usize, curl::easy::WriteError> {
        drop(self.send_header.take()); // signal header readers to stop trying
        match self.send_data.as_mut() {
            Some(writer) => writer.write_all(data).map(|_| data.len()).or(Ok(0)),
            None => Ok(0), // nothing more to receive, reader is done
        }
    }
    fn read(&mut self, data: &mut [u8]) -> Result<usize, curl::easy::ReadError> {
        match self.receive_body.as_mut() {
            Some(reader) => reader.read(data).map_err(|_err| curl::easy::ReadError::Abort),
            None => Ok(0), // nothing more to read/writer depleted
        }
    }

    fn header(&mut self, data: &[u8]) -> bool {
        match self.send_header.as_mut() {
            Some(writer) => {
                if self.checked_status {
                    writer.write_all(data).is_ok()
                } else {
                    self.checked_status = true;
                    match Handler::parse_status(data) {
                        None => true,
                        Some((status, err)) => {
                            writer
                                .channel
                                .send(Err(io::Error::new(
                                    if status == 401 {
                                        io::ErrorKind::PermissionDenied
                                    } else {
                                        io::ErrorKind::Other
                                    },
                                    err,
                                )))
                                .ok();
                            false
                        }
                    }
                }
            }
            None => false,
        }
    }
}

pub struct Request {
    pub url: String,
    pub headers: curl::easy::List,
    pub upload: bool,
}

pub struct Response {
    pub headers: pipe::Reader,
    pub body: pipe::Reader,
    pub upload_body: pipe::Writer,
}

pub fn new() -> (
    thread::JoinHandle<Result<(), curl::Error>>,
    SyncSender<Request>,
    Receiver<Response>,
) {
    let (req_send, req_recv) = sync_channel(0);
    let (res_send, res_recv) = sync_channel(0);
    let handle = std::thread::spawn(move || -> Result<(), curl::Error> {
        let mut handle = Easy2::new(Handler::default());

        for Request { url, headers, upload } in req_recv {
            handle.url(&url)?;

            // GitHub sends 'chunked' to avoid unknown clients to choke on the data, I suppose
            handle.post(upload)?;
            handle.http_headers(headers)?;
            handle.transfer_encoding(false)?;
            handle.connect_timeout(Duration::from_secs(20))?;
            // handle.proxy("http://localhost:9090")?; // DEBUG
            let low_bytes_per_second = 1024;
            handle.low_speed_limit(low_bytes_per_second)?;
            handle.low_speed_time(Duration::from_secs(20))?;

            let (receive_data, receive_headers, send_body) = {
                let handler = handle.get_mut();
                let (send, receive_data) = pipe::unidirectional(1);
                handler.send_data = Some(send);
                let (send, receive_headers) = pipe::unidirectional(1);
                handler.send_header = Some(send);
                let (send_body, receive_body) = pipe::unidirectional(None);
                handler.receive_body = Some(receive_body);
                (receive_data, receive_headers, send_body)
            };

            if res_send
                .send(Response {
                    headers: receive_headers,
                    body: receive_data,
                    upload_body: send_body,
                })
                .is_err()
            {
                break;
            }

            #[allow(clippy::branches_sharing_code)]
            if let Err(err) = handle.perform() {
                let handler = handle.get_mut();
                handler.reset();
                let err = Err(io::Error::new(io::ErrorKind::Other, err));
                handler.receive_body.take();
                match (handler.send_header.take(), handler.send_data.take()) {
                    (Some(header), mut data) => {
                        if let Err(TrySendError::Disconnected(err)) | Err(TrySendError::Full(err)) =
                            header.channel.try_send(err)
                        {
                            if let Some(body) = data.take() {
                                body.channel.try_send(err).ok();
                            }
                        }
                    }
                    (None, Some(body)) => {
                        body.channel.try_send(err).ok();
                    }
                    (None, None) => {}
                };
            } else {
                let handler = handle.get_mut();
                handler.reset();
                handler.receive_body.take();
                handler.send_header.take();
                handler.send_data.take();
            }
        }
        Ok(())
    });
    (handle, req_send, res_recv)
}

impl From<curl::Error> for http::Error {
    fn from(err: curl::Error) -> Self {
        http::Error::Detail(err.to_string())
    }
}