use bincode;
use middleman::Middleman;
use mio::{
    net::{TcpListener, TcpStream},
    Events, Poll, PollOpt, Ready, Token,
};
use mio_extras::channel::{channel, Receiver, Sender};
use serde;
use std::{
    collections::VecDeque,
    convert::TryFrom,
    fmt,
    io::{self, Read, Write},
    net::{Shutdown, SocketAddr},
    sync::mpsc::TryRecvError,
    thread,
    time::Duration,
};

#[derive(Clone, Debug, PartialEq)]
pub enum Error {
    Disconnect,
    Network,
    InvalidMsg,
    Internal,
}

impl From<io::Error> for Error {
    fn from(err: io::Error) -> Self { Error::Network }
}

impl From<TryRecvError> for Error {
    fn from(err: TryRecvError) -> Self { Error::Internal }
}

impl From<bincode::ErrorKind> for Error {
    fn from(err: bincode::ErrorKind) -> Self { Error::InvalidMsg }
}

impl<T> From<mio_extras::channel::SendError<T>> for Error {
    fn from(err: mio_extras::channel::SendError<T>) -> Self { Error::Internal }
}

pub trait PostSend = 'static + serde::Serialize + Send + middleman::Message;
pub trait PostRecv = 'static + serde::de::DeserializeOwned + Send + middleman::Message;

const TCP_TOK: Token = Token(0);
const CTRL_TOK: Token = Token(1);
const POSTBOX_TOK: Token = Token(2);
const SEND_TOK: Token = Token(3);
const RECV_TOK: Token = Token(4);
const MIDDLEMAN_TOK: Token = Token(5);

const MAX_MSG_BYTES: usize = 1 << 28;

enum CtrlMsg {
    Shutdown,
}

pub struct PostOffice<S: PostSend, R: PostRecv> {
    worker: Option<thread::JoinHandle<Result<(), Error>>>,
    ctrl_tx: Sender<CtrlMsg>,
    postbox_rx: Receiver<Result<PostBox<S, R>, Error>>,
    poll: Poll,
    err: Option<Error>,
}

impl<S: PostSend, R: PostRecv> PostOffice<S, R> {
    pub fn bind<A: Into<SocketAddr>>(addr: A) -> Result<Self, Error> {
        let tcp_listener = TcpListener::bind(&addr.into())?;

        let (ctrl_tx, ctrl_rx) = channel();
        let (postbox_tx, postbox_rx) = channel();

        let worker_poll = Poll::new()?;
        worker_poll.register(&tcp_listener, TCP_TOK, Ready::readable(), PollOpt::edge())?;
        worker_poll.register(&ctrl_rx, CTRL_TOK, Ready::readable(), PollOpt::edge())?;

        let office_poll = Poll::new()?;
        office_poll.register(&postbox_rx, POSTBOX_TOK, Ready::readable(), PollOpt::edge())?;

        let worker =
            thread::spawn(move || office_worker(worker_poll, tcp_listener, ctrl_rx, postbox_tx));

        Ok(Self {
            worker: Some(worker),
            ctrl_tx,
            postbox_rx,
            poll: office_poll,
            err: None,
        })
    }

    pub fn error(&self) -> Option<Error> { self.err.clone() }

    pub fn new_connections(&mut self) -> impl ExactSizeIterator<Item = PostBox<S, R>> {
        let mut conns = VecDeque::new();

        if self.err.is_some() {
            return conns.into_iter();
        }

        let mut events = Events::with_capacity(64);
        if let Err(err) = self.poll.poll(&mut events, Some(Duration::new(0, 0))) {
            self.err = Some(err.into());
            return conns.into_iter();
        }

        for event in events {
            match event.token() {
                // Keep reading new postboxes from the channel
                POSTBOX_TOK => loop {
                    match self.postbox_rx.try_recv() {
                        Ok(Ok(conn)) => conns.push_back(conn),
                        Err(TryRecvError::Empty) => break,
                        Err(err) => {
                            self.err = Some(err.into());
                            return conns.into_iter();
                        },
                        Ok(Err(err)) => {
                            self.err = Some(err);
                            return conns.into_iter();
                        },
                    }
                },
                tok => panic!("Unexpected event token '{:?}'", tok),
            }
        }

        conns.into_iter()
    }
}

impl<S: PostSend, R: PostRecv> Drop for PostOffice<S, R> {
    fn drop(&mut self) {
        let _ = self.ctrl_tx.send(CtrlMsg::Shutdown);
        let _ = self.worker.take().map(|w| w.join());
    }
}

fn office_worker<S: PostSend, R: PostRecv>(
    poll: Poll,
    tcp_listener: TcpListener,
    ctrl_rx: Receiver<CtrlMsg>,
    postbox_tx: Sender<Result<PostBox<S, R>, Error>>,
) -> Result<(), Error> {
    let mut events = Events::with_capacity(64);
    loop {
        if let Err(err) = poll.poll(&mut events, None) {
            postbox_tx.send(Err(err.into()))?;
            return Ok(());
        }

        for event in &events {
            match event.token() {
                CTRL_TOK => loop {
                    match ctrl_rx.try_recv() {
                        Ok(CtrlMsg::Shutdown) => return Ok(()),
                        Err(TryRecvError::Empty) => {},
                        Err(err) => {
                            postbox_tx.send(Err(err.into()))?;
                            return Ok(());
                        },
                    }
                },
                TCP_TOK => postbox_tx.send(match tcp_listener.accept() {
                    Ok((stream, _)) => PostBox::from_tcpstream(stream),
                    Err(err) => Err(err.into()),
                })?,
                tok => panic!("Unexpected event token '{:?}'", tok),
            }
        }
    }
}

pub struct PostBox<S: PostSend, R: PostRecv> {
    worker: Option<thread::JoinHandle<Result<(), Error>>>,
    ctrl_tx: Sender<CtrlMsg>,
    send_tx: Sender<S>,
    recv_rx: Receiver<Result<R, Error>>,
    poll: Poll,
    err: Option<Error>,
}

impl<S: PostSend, R: PostRecv> PostBox<S, R> {
    pub fn to_server<A: Into<SocketAddr>>(addr: A) -> Result<Self, Error> {
        Self::from_tcpstream(TcpStream::from_stream(std::net::TcpStream::connect(
            &addr.into(),
        )?)?)
    }

    fn from_tcpstream(tcp_stream: TcpStream) -> Result<Self, Error> {
        let (ctrl_tx, ctrl_rx) = channel();
        let (send_tx, send_rx) = channel();
        let (recv_tx, recv_rx) = channel();

        let worker_poll = Poll::new()?;
        worker_poll.register(
            &tcp_stream,
            TCP_TOK,
            Ready::readable() | Ready::writable(),
            PollOpt::edge(),
        )?;
        worker_poll.register(&ctrl_rx, CTRL_TOK, Ready::readable(), PollOpt::edge())?;
        worker_poll.register(&send_rx, SEND_TOK, Ready::readable(), PollOpt::edge())?;

        let postbox_poll = Poll::new()?;
        postbox_poll.register(&recv_rx, RECV_TOK, Ready::readable(), PollOpt::edge())?;

        let worker = thread::spawn(move || {
            postbox_worker(worker_poll, tcp_stream, ctrl_rx, send_rx, recv_tx)
        });

        Ok(Self {
            worker: Some(worker),
            ctrl_tx,
            send_tx,
            recv_rx,
            poll: postbox_poll,
            err: None,
        })
    }

    pub fn error(&self) -> Option<Error> { self.err.clone() }

    pub fn send(&mut self, data: S) { let _ = self.send_tx.send(data); }

    // TODO: This method is super messy.
    pub fn next_message(&mut self) -> Option<R> {
        if self.err.is_some() {
            return None;
        }

        loop {
            let mut events = Events::with_capacity(10);
            if let Err(err) = self.poll.poll(&mut events, Some(Duration::new(0, 0))) {
                self.err = Some(err.into());
                return None;
            }

            for event in events {
                match event.token() {
                    // Keep reading new messages from the channel
                    RECV_TOK => loop {
                        match self.recv_rx.try_recv() {
                            Ok(Ok(msg)) => return Some(msg),
                            Err(TryRecvError::Empty) => break,
                            Err(err) => {
                                self.err = Some(err.into());
                                return None;
                            },
                            Ok(Err(err)) => {
                                self.err = Some(err);
                                return None;
                            },
                        }
                    },
                    tok => panic!("Unexpected event token '{:?}'", tok),
                }
            }
        }
    }

    pub fn new_messages(&mut self) -> impl ExactSizeIterator<Item = R> {
        let mut msgs = VecDeque::new();

        if self.err.is_some() {
            return msgs.into_iter();
        }

        let mut events = Events::with_capacity(64);
        if let Err(err) = self.poll.poll(&mut events, Some(Duration::new(0, 0))) {
            self.err = Some(err.into());
            return msgs.into_iter();
        }

        for event in events {
            match event.token() {
                // Keep reading new messages from the channel
                RECV_TOK => loop {
                    match self.recv_rx.try_recv() {
                        Ok(Ok(msg)) => msgs.push_back(msg),
                        Err(TryRecvError::Empty) => break,
                        Err(err) => {
                            self.err = Some(err.into());
                            return msgs.into_iter();
                        },
                        Ok(Err(err)) => {
                            self.err = Some(err);
                            return msgs.into_iter();
                        },
                    }
                },
                tok => panic!("Unexpected event token '{:?}'", tok),
            }
        }

        msgs.into_iter()
    }
}

impl<S: PostSend, R: PostRecv> Drop for PostBox<S, R> {
    fn drop(&mut self) {
        let _ = self.ctrl_tx.send(CtrlMsg::Shutdown);
        let _ = self.worker.take().map(|w| w.join());
    }
}

fn postbox_worker<S: PostSend, R: PostRecv>(
    poll: Poll,
    mut tcp_stream: TcpStream,
    ctrl_rx: Receiver<CtrlMsg>,
    send_rx: Receiver<S>,
    recv_tx: Sender<Result<R, Error>>,
) -> Result<(), Error> {
    fn try_tcp_send(
        tcp_stream: &mut TcpStream,
        chunks: &mut VecDeque<Vec<u8>>,
    ) -> Result<(), Error> {
        loop {
            let chunk = match chunks.pop_front() {
                Some(chunk) => chunk,
                None => break,
            };

            match tcp_stream.write_all(&chunk) {
                Ok(()) => {},
                Err(err) if err.kind() == io::ErrorKind::WouldBlock => {
                    chunks.push_front(chunk);
                    break;
                },
                Err(err) => {
                    println!("Error: {:?}", err);
                    return Err(err.into());
                },
            }
        }

        Ok(())
    }

    enum RecvState {
        ReadHead(Vec<u8>),
        ReadBody(usize, Vec<u8>),
    }

    let mut recv_state = RecvState::ReadHead(Vec::new());
    let mut chunks = VecDeque::new();

    //let mut recv_state = RecvState::ReadHead(Vec::with_capacity(8));
    let mut events = Events::with_capacity(64);

    'work: loop {
        if let Err(err) = poll.poll(&mut events, None) {
            recv_tx.send(Err(err.into()))?;
            break 'work;
        }

        for event in &events {
            match event.token() {
                CTRL_TOK => match ctrl_rx.try_recv() {
                    Ok(CtrlMsg::Shutdown) => {
                        break 'work;
                    },
                    Err(TryRecvError::Empty) => (),
                    Err(err) => {
                        recv_tx.send(Err(err.into()))?;
                        break 'work;
                    },
                },
                SEND_TOK => loop {
                    match send_rx.try_recv() {
                        Ok(outgoing_msg) => {
                            let mut msg_bytes = match bincode::serialize(&outgoing_msg) {
                                Ok(bytes) => bytes,
                                Err(err) => {
                                    recv_tx.send(Err((*err).into()))?;
                                    break 'work;
                                },
                            };

                            let mut bytes = msg_bytes.len().to_le_bytes().as_ref().to_vec();
                            bytes.append(&mut msg_bytes);

                            bytes
                                .chunks(1024)
                                .map(|chunk| chunk.to_vec())
                                .for_each(|chunk| chunks.push_back(chunk));

                            match try_tcp_send(&mut tcp_stream, &mut chunks) {
                                Ok(_) => {},
                                Err(err) => {
                                    recv_tx.send(Err(err.into()))?;
                                    return Err(Error::Network);
                                },
                            }
                        },
                        Err(TryRecvError::Empty) => break,
                        Err(err) => Err(err)?,
                    }
                },
                TCP_TOK => {
                    loop {
                        // Check TCP error
                        match tcp_stream.take_error() {
                            Ok(None) => {},
                            Ok(Some(err)) => {
                                recv_tx.send(Err(err.into()))?;
                                break 'work;
                            },
                            Err(err) => {
                                recv_tx.send(Err(err.into()))?;
                                break 'work;
                            },
                        }
                        match &mut recv_state {
                            RecvState::ReadHead(head) => {
                                if head.len() == 8 {
                                    let len = usize::from_le_bytes(
                                        <[u8; 8]>::try_from(head.as_slice()).unwrap(),
                                    );
                                    if len > MAX_MSG_BYTES {
                                        println!("TOO BIG! {:x}", len);
                                        recv_tx.send(Err(Error::InvalidMsg))?;
                                        break 'work;
                                    } else if len == 0 {
                                        recv_state = RecvState::ReadHead(Vec::with_capacity(8));
                                        break;
                                    } else {
                                        recv_state = RecvState::ReadBody(len, Vec::new());
                                    }
                                } else {
                                    let mut b = [0; 1];
                                    match tcp_stream.read(&mut b) {
                                        Ok(0) => {},
                                        Ok(_) => head.push(b[0]),
                                        Err(_) => break,
                                    }
                                }
                            },
                            RecvState::ReadBody(len, body) => {
                                if body.len() == *len {
                                    match bincode::deserialize(&body) {
                                        Ok(msg) => {
                                            recv_tx.send(Ok(msg))?;
                                            recv_state = RecvState::ReadHead(Vec::with_capacity(8));
                                        },
                                        Err(err) => {
                                            recv_tx.send(Err((*err).into()))?;
                                            break 'work;
                                        },
                                    }
                                } else {
                                    let left = *len - body.len();
                                    let mut buf = vec![0; left];
                                    match tcp_stream.read(&mut buf) {
                                        Ok(_) => body.append(&mut buf),
                                        Err(err) => {
                                            recv_tx.send(Err(err.into()))?;
                                            break 'work;
                                        },
                                    }
                                }
                            },
                        }
                    }

                    // Now, try sending TCP stuff
                    match try_tcp_send(&mut tcp_stream, &mut chunks) {
                        Ok(_) => {},
                        Err(err) => {
                            recv_tx.send(Err(err.into()))?;
                            return Err(Error::Network);
                        },
                    }
                },
                tok => panic!("Unexpected event token '{:?}'", tok),
            }
        }
    }

    //tcp_stream.shutdown(Shutdown::Both)?;
    Ok(())
}

// TESTS

/*
#[derive(Serialize, Deserialize)]
struct TestMsg<T>(T);

#[test]
fn connect() {
    let srv_addr = ([127, 0, 0, 1], 12345);

    let mut postoffice = PostOffice::<TestMsg<u32>, TestMsg<f32>>::bind(srv_addr).unwrap();

    // We should start off with 0 incoming connections.
    thread::sleep(Duration::from_millis(250));
    assert_eq!(postoffice.new_connections().len(), 0);
    assert_eq!(postoffice.error(), None);

    let postbox = PostBox::<TestMsg<f32>, TestMsg<u32>>::to_server(srv_addr).unwrap();

    // Now a postbox has been created, we should have 1 new.
    thread::sleep(Duration::from_millis(250));
    let incoming = postoffice.new_connections();
    assert_eq!(incoming.len(), 1);
    assert_eq!(postoffice.error(), None);
}

#[test]
fn connect_fail() {
    let listen_addr = ([0; 4], 12345);
    let connect_addr = ([127, 0, 0, 1], 12212);

    let mut postoffice = PostOffice::<TestMsg<u32>, TestMsg<f32>>::bind(listen_addr).unwrap();

    // We should start off with 0 incoming connections.
    thread::sleep(Duration::from_millis(250));
    assert_eq!(postoffice.new_connections().len(), 0);
    assert_eq!(postoffice.error(), None);

    assert!(PostBox::<TestMsg<f32>, TestMsg<u32>>::to_server(connect_addr).is_err());
}

#[test]
fn connection_count() {
    let srv_addr = ([127, 0, 0, 1], 12346);

    let mut postoffice = PostOffice::<TestMsg<u32>, TestMsg<f32>>::bind(srv_addr).unwrap();
    let mut postboxes = Vec::new();

    // We should start off with 0 incoming connections.
    thread::sleep(Duration::from_millis(250));
    assert_eq!(postoffice.new_connections().len(), 0);
    assert_eq!(postoffice.error(), None);

    for _ in 0..5 {
        postboxes.push(PostBox::<TestMsg<f32>, TestMsg<u32>>::to_server(srv_addr).unwrap());
    }

    // 5 postboxes created, we should have 5.
    thread::sleep(Duration::from_millis(3500));
    let incoming = postoffice.new_connections();
    assert_eq!(incoming.len(), 5);
    assert_eq!(postoffice.error(), None);
}

#[test]
fn disconnect() {
    let srv_addr = ([127, 0, 0, 1], 12347);

    let mut postoffice = PostOffice::<TestMsg<u32>, TestMsg<f32>>::bind(srv_addr).unwrap();

    let mut server_postbox = {
        let mut client_postbox = PostBox::<TestMsg<f32>, TestMsg<u32>>::to_server(srv_addr).unwrap();

        thread::sleep(Duration::from_millis(250));
        let mut incoming = postoffice.new_connections();
        assert_eq!(incoming.len(), 1);
        assert_eq!(postoffice.error(), None);

        incoming.next().unwrap()
    };

    // The client postbox has since been disconnected.
    thread::sleep(Duration::from_millis(2050));
    let incoming_msgs = server_postbox.new_messages();
    assert_eq!(incoming_msgs.len(), 0);
    // TODO
    // assert_eq!(server_postbox.error(), Some(Error::Disconnect));
}

#[test]
fn client_to_server() {
    let srv_addr = ([127, 0, 0, 1], 12348);

    let mut po = PostOffice::<TestMsg<u32>, TestMsg<f32>>::bind(srv_addr).unwrap();

    let mut client_pb = PostBox::<TestMsg<f32>, TestMsg<u32>>::to_server(srv_addr).unwrap();

    thread::sleep(Duration::from_millis(250));

    let mut server_pb = po.new_connections().next().unwrap();

    client_pb.send(TestMsg(1337.0));
    client_pb.send(TestMsg(9821.0));
    client_pb.send(TestMsg(-3.2));
    client_pb.send(TestMsg(17.0));

    thread::sleep(Duration::from_millis(250));

    let mut incoming_msgs = server_pb.new_messages();
    assert_eq!(incoming_msgs.len(), 4);
    assert_eq!(incoming_msgs.next().unwrap(), TestMsg(1337.0));
    assert_eq!(incoming_msgs.next().unwrap(), TestMsg(9821.0));
    assert_eq!(incoming_msgs.next().unwrap(), TestMsg(-3.2));
    assert_eq!(incoming_msgs.next().unwrap(), TestMsg(17.0));
}

#[test]
fn server_to_client() {
    let srv_addr = ([127, 0, 0, 1], 12349);

    let mut po = PostOffice::<TestMsg<u32>, TestMsg<f32>>::bind(srv_addr).unwrap();

    let mut client_pb = PostBox::<TestMsg<f32>, TestMsg<u32>>::to_server(srv_addr).unwrap();

    thread::sleep(Duration::from_millis(250));

    let mut server_pb = po.new_connections().next().unwrap();

    server_pb.send(TestMsg(1337));
    server_pb.send(TestMsg(9821));
    server_pb.send(TestMsg(39999999));
    server_pb.send(TestMsg(17));

    thread::sleep(Duration::from_millis(250));

    let mut incoming_msgs = client_pb.new_messages();
    assert_eq!(incoming_msgs.len(), 4);
    assert_eq!(incoming_msgs.next().unwrap(), TestMsg(1337));
    assert_eq!(incoming_msgs.next().unwrap(), TestMsg(9821));
    assert_eq!(incoming_msgs.next().unwrap(), TestMsg(39999999));
    assert_eq!(incoming_msgs.next().unwrap(), TestMsg(17));
}
*/