use std::cell::RefCell;
use std::collections::BTreeMap;
use std::io::{Cursor, ErrorKind, Read, Write};
use std::net::SocketAddr;
use std::rc::Rc;
use std::sync::atomic::{AtomicUsize, Ordering};
use std::sync::Arc;
use std::time::Duration;

use aquatic_common::access_list::AccessList;
use aquatic_http_protocol::common::InfoHash;
use aquatic_http_protocol::request::{Request, RequestParseError, ScrapeRequest};
use aquatic_http_protocol::response::{
    FailureResponse, Response, ScrapeResponse, ScrapeStatistics,
};
use either::Either;
use futures_lite::{AsyncReadExt, AsyncWriteExt, StreamExt};
use glommio::channels::channel_mesh::{MeshBuilder, Partial, Role, Senders};
use glommio::channels::local_channel::{new_bounded, LocalReceiver, LocalSender};
use glommio::channels::shared_channel::ConnectedReceiver;
use glommio::net::{TcpListener, TcpStream};
use glommio::task::JoinHandle;
use glommio::timer::TimerActionRepeat;
use glommio::{enclose, prelude::*};
use rustls::ServerConnection;
use slab::Slab;

use crate::common::num_digits_in_usize;
use crate::config::Config;

use super::common::*;

const INTERMEDIATE_BUFFER_SIZE: usize = 1024;
const MAX_REQUEST_SIZE: usize = 2048;

struct PendingScrapeResponse {
    pending_worker_responses: usize,
    stats: BTreeMap<InfoHash, ScrapeStatistics>,
}

struct ConnectionReference {
    response_sender: LocalSender<ChannelResponse>,
    handle: JoinHandle<()>,
}

struct Connection {
    config: Rc<Config>,
    access_list: Rc<RefCell<AccessList>>,
    request_senders: Rc<Senders<ChannelRequest>>,
    response_receiver: LocalReceiver<ChannelResponse>,
    response_consumer_id: ConsumerId,
    tls: ServerConnection,
    stream: TcpStream,
    connection_id: ConnectionId,
    request_buffer: [u8; MAX_REQUEST_SIZE],
    request_buffer_position: usize,
}

pub async fn run_socket_worker(
    config: Config,
    tls_config: Arc<rustls::ServerConfig>,
    request_mesh_builder: MeshBuilder<ChannelRequest, Partial>,
    response_mesh_builder: MeshBuilder<ChannelResponse, Partial>,
    num_bound_sockets: Arc<AtomicUsize>,
    access_list: AccessList,
) {
    let config = Rc::new(config);
    let access_list = Rc::new(RefCell::new(access_list));

    let listener = TcpListener::bind(config.network.address).expect("bind socket");
    num_bound_sockets.fetch_add(1, Ordering::SeqCst);

    let (request_senders, _) = request_mesh_builder.join(Role::Producer).await.unwrap();
    let request_senders = Rc::new(request_senders);

    let (_, mut response_receivers) = response_mesh_builder.join(Role::Consumer).await.unwrap();
    let response_consumer_id = ConsumerId(response_receivers.consumer_id().unwrap());

    let connection_slab = Rc::new(RefCell::new(Slab::new()));
    let connections_to_remove = Rc::new(RefCell::new(Vec::new()));

    // Periodically update access list
    TimerActionRepeat::repeat(enclose!((config, access_list) move || {
        enclose!((config, access_list) move || async move {
            update_access_list(config.clone(), access_list.clone()).await;

            Some(Duration::from_secs(config.cleaning.interval))
        })()
    }));

    // Periodically remove closed connections
    TimerActionRepeat::repeat(
        enclose!((config, connection_slab, connections_to_remove) move || {
            enclose!((config, connection_slab, connections_to_remove) move || async move {
                let connections_to_remove = connections_to_remove.replace(Vec::new());

                for connection_id in connections_to_remove {
                    if let Some(_) = connection_slab.borrow_mut().try_remove(connection_id) {
                        ::log::debug!("removed connection with id {}", connection_id);
                    } else {
                        ::log::error!(
                            "couldn't remove connection with id {}, it is not in connection slab",
                            connection_id
                        );
                    }
                }

                Some(Duration::from_secs(config.cleaning.interval))
            })()
        }),
    );

    for (_, response_receiver) in response_receivers.streams() {
        spawn_local(receive_responses(
            response_receiver,
            connection_slab.clone(),
        ))
        .detach();
    }

    let mut incoming = listener.incoming();

    while let Some(stream) = incoming.next().await {
        match stream {
            Ok(stream) => {
                let (response_sender, response_receiver) = new_bounded(config.request_workers);

                let mut slab = connection_slab.borrow_mut();
                let entry = slab.vacant_entry();
                let key = entry.key();

                let mut conn = Connection {
                    config: config.clone(),
                    access_list: access_list.clone(),
                    request_senders: request_senders.clone(),
                    response_receiver,
                    response_consumer_id,
                    tls: ServerConnection::new(tls_config.clone()).unwrap(),
                    stream,
                    connection_id: ConnectionId(entry.key()),
                    request_buffer: [0u8; MAX_REQUEST_SIZE],
                    request_buffer_position: 0,
                };

                let connections_to_remove = connections_to_remove.clone();

                let handle = spawn_local(async move {
                    if let Err(err) = conn.handle_stream().await {
                        ::log::info!("conn.handle_stream() error: {:?}", err);
                    }

                    connections_to_remove.borrow_mut().push(key);
                })
                .detach();

                let connection_reference = ConnectionReference {
                    response_sender,
                    handle,
                };

                entry.insert(connection_reference);
            }
            Err(err) => {
                ::log::error!("accept connection: {:?}", err);
            }
        }
    }
}

async fn receive_responses(
    mut response_receiver: ConnectedReceiver<ChannelResponse>,
    connection_references: Rc<RefCell<Slab<ConnectionReference>>>,
) {
    while let Some(channel_response) = response_receiver.next().await {
        if let Some(reference) = connection_references
            .borrow()
            .get(channel_response.get_connection_id().0)
        {
            if let Err(err) = reference.response_sender.try_send(channel_response) {
                ::log::error!("Couldn't send response to local receiver: {:?}", err);
            }
        }
    }
}

impl Connection {
    async fn handle_stream(&mut self) -> anyhow::Result<()> {
        let mut close_after_writing = false;

        loop {
            match self.read_tls().await? {
                Some(Either::Left(request)) => {
                    let response = match self.handle_request(request).await? {
                        Some(Either::Left(response)) => response,
                        Some(Either::Right(pending_scrape_response)) => {
                            self.wait_for_response(Some(pending_scrape_response))
                                .await?
                        }
                        None => self.wait_for_response(None).await?,
                    };

                    self.queue_response(&response)?;

                    if !self.config.network.keep_alive {
                        close_after_writing = true;
                    }
                }
                Some(Either::Right(response)) => {
                    self.queue_response(&Response::Failure(response))?;

                    close_after_writing = true;
                }
                None => {
                    // Still handshaking
                }
            }

            self.write_tls().await?;

            if close_after_writing {
                let _ = self.stream.shutdown(std::net::Shutdown::Both).await;

                break;
            }
        }

        Ok(())
    }

    async fn read_tls(&mut self) -> anyhow::Result<Option<Either<Request, FailureResponse>>> {
        loop {
            ::log::debug!("read_tls");

            let mut buf = [0u8; INTERMEDIATE_BUFFER_SIZE];

            let bytes_read = self.stream.read(&mut buf).await?;

            if bytes_read == 0 {
                return Err(anyhow::anyhow!("Peer has closed connection"));
            }

            let _ = self.tls.read_tls(&mut &buf[..bytes_read]).unwrap();

            let io_state = self.tls.process_new_packets()?;

            let mut added_plaintext = false;

            if io_state.plaintext_bytes_to_read() != 0 {
                loop {
                    match self.tls.reader().read(&mut buf) {
                        Ok(0) => {
                            break;
                        }
                        Ok(amt) => {
                            let end = self.request_buffer_position + amt;

                            if end > self.request_buffer.len() {
                                return Err(anyhow::anyhow!("request too large"));
                            } else {
                                let request_buffer_slice =
                                    &mut self.request_buffer[self.request_buffer_position..end];

                                request_buffer_slice.copy_from_slice(&buf[..amt]);

                                self.request_buffer_position = end;

                                added_plaintext = true;
                            }
                        }
                        Err(err) if err.kind() == ErrorKind::WouldBlock => {
                            break;
                        }
                        Err(err) => {
                            // Should never happen
                            ::log::error!("tls.reader().read error: {:?}", err);

                            break;
                        }
                    }
                }
            }

            if added_plaintext {
                match Request::from_bytes(&self.request_buffer[..self.request_buffer_position]) {
                    Ok(request) => {
                        ::log::debug!("received request: {:?}", request);

                        self.request_buffer_position = 0;

                        return Ok(Some(Either::Left(request)));
                    }
                    Err(RequestParseError::NeedMoreData) => {
                        ::log::debug!(
                            "need more request data. current data: {:?}",
                            std::str::from_utf8(&self.request_buffer)
                        );
                    }
                    Err(RequestParseError::Invalid(err)) => {
                        ::log::debug!("invalid request: {:?}", err);

                        let response = FailureResponse {
                            failure_reason: "Invalid request".into(),
                        };

                        return Ok(Some(Either::Right(response)));
                    }
                }
            }

            if self.tls.wants_write() {
                break;
            }
        }

        Ok(None)
    }

    async fn write_tls(&mut self) -> anyhow::Result<()> {
        if !self.tls.wants_write() {
            return Ok(());
        }

        ::log::debug!("write_tls (wants write)");

        let mut buf = Vec::new();
        let mut buf = Cursor::new(&mut buf);

        while self.tls.wants_write() {
            self.tls.write_tls(&mut buf).unwrap();
        }

        self.stream.write_all(&buf.into_inner()).await?;
        self.stream.flush().await?;

        Ok(())
    }

    /// Take a request and:
    /// - Return error response if request is not allowed
    /// - If it is an announce requests, pass it on to request workers and return None
    /// - If it is a scrape requests, split it up and pass on parts to
    ///   relevant request workers, and return PendingScrapeResponse struct.
    async fn handle_request(
        &self,
        request: Request,
    ) -> anyhow::Result<Option<Either<Response, PendingScrapeResponse>>> {
        let peer_addr = self.get_peer_addr()?;

        match request {
            Request::Announce(request) => {
                let info_hash = request.info_hash;

                if self
                    .access_list
                    .borrow()
                    .allows(self.config.access_list.mode, &info_hash.0)
                {
                    let request = ChannelRequest::Announce {
                        request,
                        connection_id: self.connection_id,
                        response_consumer_id: self.response_consumer_id,
                        peer_addr,
                    };

                    let consumer_index = calculate_request_consumer_index(&self.config, info_hash);

                    // Only fails when receiver is closed
                    self.request_senders
                        .send_to(consumer_index, request)
                        .await
                        .unwrap();

                    Ok(None)
                } else {
                    let response = Response::Failure(FailureResponse {
                        failure_reason: "Info hash not allowed".into(),
                    });

                    Ok(Some(Either::Left(response)))
                }
            }
            Request::Scrape(ScrapeRequest { info_hashes }) => {
                let mut info_hashes_by_worker: BTreeMap<usize, Vec<InfoHash>> = BTreeMap::new();

                for info_hash in info_hashes.into_iter() {
                    let info_hashes = info_hashes_by_worker
                        .entry(calculate_request_consumer_index(&self.config, info_hash))
                        .or_default();

                    info_hashes.push(info_hash);
                }

                let pending_worker_responses = info_hashes_by_worker.len();

                for (consumer_index, info_hashes) in info_hashes_by_worker {
                    let request = ChannelRequest::Scrape {
                        request: ScrapeRequest { info_hashes },
                        peer_addr,
                        response_consumer_id: self.response_consumer_id,
                        connection_id: self.connection_id,
                    };

                    // Only fails when receiver is closed
                    self.request_senders
                        .send_to(consumer_index, request)
                        .await
                        .unwrap();
                }

                let pending_scrape_response = PendingScrapeResponse {
                    pending_worker_responses,
                    stats: Default::default(),
                };

                Ok(Some(Either::Right(pending_scrape_response)))
            }
        }
    }

    /// Wait for announce response or partial scrape responses to arrive,
    /// return full response
    async fn wait_for_response(
        &self,
        mut opt_pending_scrape_response: Option<PendingScrapeResponse>,
    ) -> anyhow::Result<Response> {
        loop {
            if let Some(channel_response) = self.response_receiver.recv().await {
                if channel_response.get_peer_addr() != self.get_peer_addr()? {
                    return Err(anyhow::anyhow!("peer addressess didn't match"));
                }

                match channel_response {
                    ChannelResponse::Announce { response, .. } => {
                        break Ok(Response::Announce(response));
                    }
                    ChannelResponse::Scrape { response, .. } => {
                        if let Some(mut pending) = opt_pending_scrape_response.take() {
                            pending.stats.extend(response.files);
                            pending.pending_worker_responses -= 1;

                            if pending.pending_worker_responses == 0 {
                                let response = Response::Scrape(ScrapeResponse {
                                    files: pending.stats,
                                });

                                break Ok(response);
                            } else {
                                opt_pending_scrape_response = Some(pending);
                            }
                        } else {
                            return Err(anyhow::anyhow!(
                                "received channel scrape response without pending scrape response"
                            ));
                        }
                    }
                };
            } else {
                // TODO: this is a serious error condition and should maybe be handled differently
                return Err(anyhow::anyhow!(
                    "response receiver can't receive - sender is closed"
                ));
            }
        }
    }

    fn queue_response(&mut self, response: &Response) -> anyhow::Result<()> {
        let mut body = Vec::new();

        response.write(&mut body).unwrap();

        let content_len = body.len() + 2; // 2 is for newlines at end
        let content_len_num_digits = num_digits_in_usize(content_len);

        let mut response_bytes = Vec::with_capacity(39 + content_len_num_digits + body.len());

        response_bytes.extend_from_slice(b"HTTP/1.1 200 OK\r\nContent-Length: ");
        ::itoa::write(&mut response_bytes, content_len)?;
        response_bytes.extend_from_slice(b"\r\n\r\n");
        response_bytes.append(&mut body);
        response_bytes.extend_from_slice(b"\r\n");

        self.tls.writer().write(&response_bytes[..])?;

        Ok(())
    }

    fn get_peer_addr(&self) -> anyhow::Result<SocketAddr> {
        self.stream
            .peer_addr()
            .map_err(|err| anyhow::anyhow!("Couldn't get peer addr: {:?}", err))
    }
}

fn calculate_request_consumer_index(config: &Config, info_hash: InfoHash) -> usize {
    (info_hash.0[0] as usize) % config.request_workers
}