#![deny(
    missing_docs,
    missing_debug_implementations,
    missing_copy_implementations,
    trivial_casts,
    trivial_numeric_casts,
    unsafe_code,
    unstable_features,
    unused_import_braces,
    unused_qualifications
)]

//!
//! libFenrir is the official rust library implementing the Fenrir protocol

pub mod auth;
mod config;
pub mod connection;
pub mod dnssec;
pub mod enc;
mod inner;

use ::std::{sync::Arc, vec::Vec};
use ::tokio::{net::UdpSocket, sync::Mutex};

use crate::{
    auth::{Domain, ServiceID, TokenChecker},
    connection::{
        handshake,
        socket::{SocketList, UdpClient, UdpServer},
        AuthServerConnections, Packet,
    },
    inner::{
        worker::{ConnectInfo, RawUdp, Work, Worker},
        ThreadTracker,
    },
};
pub use config::Config;

/// Main fenrir library errors
#[derive(::thiserror::Error, Debug)]
pub enum Error {
    /// The library was not initialized (run .start())
    #[error("not initialized")]
    NotInitialized,
    /// Error in setting up worker threads
    #[error("Setup err: {0}")]
    Setup(String),
    /// General I/O error
    #[error("IO: {0:?}")]
    IO(#[from] ::std::io::Error),
    /// Dnssec errors
    #[error("Dnssec: {0:?}")]
    Dnssec(#[from] dnssec::Error),
    /// Handshake errors
    #[error("Handshake: {0:?}")]
    Handshake(#[from] handshake::Error),
    /// Key error
    #[error("key: {0:?}")]
    Key(#[from] crate::enc::Error),
    /// Resolution problems. wrong or incomplete DNSSEC data
    #[error("DNSSEC resolution: {0}")]
    Resolution(String),
    /// Wrapper on encryption errors
    #[error("Encrypt: {0}")]
    Encrypt(enc::Error),
}

/// Instance of a fenrir endpoint
#[allow(missing_copy_implementations, missing_debug_implementations)]
pub struct Fenrir {
    /// library Configuration
    cfg: Config,
    /// listening udp sockets
    sockets: SocketList,
    /// DNSSEC resolver, with failovers
    dnssec: Option<dnssec::Dnssec>,
    /// Broadcast channel to tell workers to stop working
    stop_working: ::tokio::sync::broadcast::Sender<bool>,
    /// where to ask for token check
    token_check: Option<Arc<::tokio::sync::Mutex<TokenChecker>>>,
    /// tracks the connections to authentication servers
    /// so that we can reuse them
    conn_auth_srv: Mutex<AuthServerConnections>,
    // TODO: find a way to both increase and decrease these two in a thread-safe
    // manner
    _thread_pool: Vec<::std::thread::JoinHandle<()>>,
    _thread_work: Arc<Vec<::async_channel::Sender<Work>>>,
}

// TODO: graceful vs immediate stop

impl Drop for Fenrir {
    fn drop(&mut self) {
        self.stop_sync()
    }
}

impl Fenrir {
    /// Create a new Fenrir endpoint
    pub fn new(config: &Config) -> Result<Self, Error> {
        let (sender, _) = ::tokio::sync::broadcast::channel(1);
        let endpoint = Fenrir {
            cfg: config.clone(),
            sockets: SocketList::new(),
            dnssec: None,
            stop_working: sender,
            token_check: None,
            conn_auth_srv: Mutex::new(AuthServerConnections::new()),
            _thread_pool: Vec::new(),
            _thread_work: Arc::new(Vec::new()),
        };
        Ok(endpoint)
    }

    /// Start all workers, listeners
    pub async fn start(
        &mut self,
        tokio_rt: Arc<::tokio::runtime::Runtime>,
    ) -> Result<(), Error> {
        self.start_work_threads_pinned(tokio_rt).await?;
        if let Err(e) = self.add_sockets().await {
            self.stop().await;
            return Err(e.into());
        }
        self.dnssec = Some(dnssec::Dnssec::new(&self.cfg.resolvers).await?);
        Ok(())
    }

    /// Stop all workers, listeners
    /// asyncronous version for Drop
    fn stop_sync(&mut self) {
        let _ = self.stop_working.send(true);
        let toempty_sockets = self.sockets.rm_all();
        let task = ::tokio::task::spawn(toempty_sockets.stop_all());
        let _ = ::futures::executor::block_on(task);
        let mut old_thread_pool = Vec::new();
        ::std::mem::swap(&mut self._thread_pool, &mut old_thread_pool);
        let _ = old_thread_pool.into_iter().map(|th| th.join());
        self.dnssec = None;
    }

    /// Stop all workers, listeners
    pub async fn stop(&mut self) {
        let _ = self.stop_working.send(true);
        let toempty_sockets = self.sockets.rm_all();
        toempty_sockets.stop_all().await;
        let mut old_thread_pool = Vec::new();
        ::std::mem::swap(&mut self._thread_pool, &mut old_thread_pool);
        let _ = old_thread_pool.into_iter().map(|th| th.join());
        self.dnssec = None;
    }
    /// Add all UDP sockets found in config
    /// and start listening for packets
    async fn add_sockets(&self) -> ::std::io::Result<()> {
        let sockets = self.cfg.listen.iter().map(|s_addr| async {
            let socket =
                ::tokio::spawn(connection::socket::bind_udp(s_addr.clone()))
                    .await??;
            Ok(socket)
        });
        let sockets = ::futures::future::join_all(sockets).await;
        for s_res in sockets.into_iter() {
            match s_res {
                Ok(s) => {
                    let stop_working = self.stop_working.subscribe();
                    let arc_s = Arc::new(s);
                    let join = ::tokio::spawn(Self::listen_udp(
                        stop_working,
                        self._thread_work.clone(),
                        arc_s.clone(),
                    ));
                    self.sockets.add_socket(arc_s, join).await;
                }
                Err(e) => {
                    return Err(e);
                }
            }
        }
        Ok(())
    }

    /// Run a dedicated loop to read packets on the listening socket
    async fn listen_udp(
        mut stop_working: ::tokio::sync::broadcast::Receiver<bool>,
        work_queues: Arc<Vec<::async_channel::Sender<Work>>>,
        socket: Arc<UdpSocket>,
    ) -> ::std::io::Result<()> {
        // jumbo frames are 9K max
        let sock_receiver = UdpServer(socket.local_addr()?);
        let mut buffer: [u8; 9000] = [0; 9000];
        let queues_num = work_queues.len() as u64;
        loop {
            let (bytes, sock_sender) = ::tokio::select! {
                _done = stop_working.recv() => {
                    break;
                }
                result = socket.recv_from(&mut buffer) => {
                    result?
                }
            };
            let data: Vec<u8> = buffer[..bytes].to_vec();

            // we very likely have multiple threads, pinned to different cpus.
            // use the ConnectionID to send the same connection
            // to the same thread.
            // Handshakes have connection ID 0, so we use the sender's UDP port

            let packet = match Packet::deserialize_id(&data) {
                Ok(packet) => packet,
                Err(_) => continue, // packet way too short, ignore.
            };
            let thread_idx: usize = {
                use connection::packet::ConnectionID;
                match packet.id {
                    ConnectionID::Handshake => {
                        let send_port = sock_sender.port() as u64;
                        ((send_port % queues_num) - 1) as usize
                    }
                    ConnectionID::ID(id) => {
                        ((id.get() % queues_num) - 1) as usize
                    }
                }
            };
            let _ = work_queues[thread_idx]
                .send(Work::Recv(RawUdp {
                    src: UdpClient(sock_sender),
                    dst: sock_receiver,
                    packet,
                    data,
                }))
                .await;
        }
        Ok(())
    }
    /// Get the raw TXT record of a Fenrir domain
    pub async fn resolv_txt(&self, domain: &Domain) -> Result<String, Error> {
        match &self.dnssec {
            Some(dnssec) => Ok(dnssec.resolv(domain).await?),
            None => Err(Error::NotInitialized),
        }
    }

    /// Get the raw TXT record of a Fenrir domain
    pub async fn resolv(
        &self,
        domain: &Domain,
    ) -> Result<dnssec::Record, Error> {
        let record_str = self.resolv_txt(domain).await?;
        Ok(dnssec::Dnssec::parse_txt_record(&record_str)?)
    }

    /// Connect to a service
    pub async fn connect(
        &self,
        domain: &Domain,
        service: ServiceID,
    ) -> Result<(), Error> {
        let resolved = self.resolv(domain).await?;
        loop {
            // check if we already have a connection to that auth. srv
            let is_reserved = {
                let mut conn_auth_lock = self.conn_auth_srv.lock().await;
                conn_auth_lock.get_or_reserve(&resolved)
            };
            use connection::Reservation;
            match is_reserved {
                Reservation::Waiting => {
                    use ::std::time::Duration;
                    use ::tokio::time::sleep;
                    // PERF: exponential backoff.
                    // or we can have a broadcast channel
                    sleep(Duration::from_millis(50)).await;
                    continue;
                }
                Reservation::Reserved => break,
                Reservation::Present(_id_send) => {
                    //TODO: reuse connection
                    todo!()
                }
            }
        }
        // Spot reserved for the connection

        // find the thread with less connections
        let th_num = self._thread_work.len();
        let mut conn_count = Vec::<usize>::with_capacity(th_num);
        let mut wait_res =
            Vec::<::tokio::sync::oneshot::Receiver<usize>>::with_capacity(
                th_num,
            );
        for th in self._thread_work.iter() {
            let (send, recv) = ::tokio::sync::oneshot::channel();
            wait_res.push(recv);
            let _ = th.send(Work::CountConnections(send)).await;
        }
        for ch in wait_res.into_iter() {
            if let Ok(conn_num) = ch.await {
                conn_count.push(conn_num);
            }
        }
        if conn_count.len() != th_num {
            return Err(Error::IO(::std::io::Error::new(
                ::std::io::ErrorKind::NotConnected,
                "can't connect to a thread",
            )));
        }
        let thread_idx = conn_count
            .iter()
            .enumerate()
            .max_by(|(_, a), (_, b)| a.cmp(b))
            .map(|(index, _)| index)
            .unwrap();

        // and tell that thread to connect somewhere
        let (send, recv) = ::tokio::sync::oneshot::channel();
        let _ = self._thread_work[thread_idx]
            .send(Work::Connect(ConnectInfo {
                answer: send,
                resolved: resolved.clone(),
                service_id: service,
                domain: domain.clone(),
            }))
            .await;

        match recv.await {
            Ok(res) => {
                match res {
                    Err(e) => {
                        let mut conn_auth_lock =
                            self.conn_auth_srv.lock().await;
                        conn_auth_lock.remove_reserved(&resolved);
                        Err(e)
                    }
                    Ok((pubkey, id_send)) => {
                        let mut conn_auth_lock =
                            self.conn_auth_srv.lock().await;
                        conn_auth_lock.add(&pubkey, id_send, &resolved);

                        //FIXME: user needs to somehow track the connection
                        Ok(())
                    }
                }
            }
            Err(e) => {
                // Thread dropped the sender. no more thread?
                let mut conn_auth_lock = self.conn_auth_srv.lock().await;
                conn_auth_lock.remove_reserved(&resolved);
                Err(Error::IO(::std::io::Error::new(
                    ::std::io::ErrorKind::Interrupted,
                    "recv failure on connect: ".to_owned() + &e.to_string(),
                )))
            }
        }
    }

    // TODO: start work on a LocalSet provided by the user
    /// Start one working thread for each physical cpu
    /// threads are pinned to each cpu core.
    /// Work will be divided and rerouted so that there is no need to lock
    async fn start_work_threads_pinned(
        &mut self,
        tokio_rt: Arc<::tokio::runtime::Runtime>,
    ) -> ::std::result::Result<(), Error> {
        use ::std::sync::Mutex;
        let hw_topology = match ::hwloc2::Topology::new() {
            Some(hw_topology) => Arc::new(Mutex::new(hw_topology)),
            None => {
                return Err(Error::Setup(
                    "Can't get hardware topology".to_owned(),
                ))
            }
        };
        let cores;
        {
            let topology_lock = hw_topology.lock().unwrap();
            let all_cores = match topology_lock
                .objects_with_type(&::hwloc2::ObjectType::Core)
            {
                Ok(all_cores) => all_cores,
                Err(_) => {
                    return Err(Error::Setup("can't list cores".to_owned()))
                }
            };
            cores = all_cores.len();
            if cores <= 0 || !topology_lock.support().cpu().set_thread() {
                ::tracing::error!("No support for CPU pinning");
                return Err(Error::Setup("No cpu pinning support".to_owned()));
            }
        }
        for core in 0..cores {
            ::tracing::debug!("Spawning thread {}", core);
            let th_topology = hw_topology.clone();
            let th_tokio_rt = tokio_rt.clone();
            let th_config = self.cfg.clone();
            let (work_send, work_recv) = ::async_channel::unbounded::<Work>();
            let th_stop_working = self.stop_working.subscribe();
            let th_token_check = self.token_check.clone();
            let th_socket_addrs = self.cfg.listen.clone();
            let thread_id = ThreadTracker {
                total: cores as u16,
                id: 1 + (core as u16),
            };

            let join_handle = ::std::thread::spawn(move || {
                // bind to a specific core
                let th_pinning;
                {
                    let mut th_topology_lock = th_topology.lock().unwrap();
                    let th_cores = th_topology_lock
                        .objects_with_type(&::hwloc2::ObjectType::Core)
                        .unwrap();
                    let cpuset = th_cores.get(core).unwrap().cpuset().unwrap();
                    th_pinning = th_topology_lock.set_cpubind(
                        cpuset,
                        ::hwloc2::CpuBindFlags::CPUBIND_THREAD,
                    );
                }
                match th_pinning {
                    Ok(_) => {}
                    Err(_) => {
                        ::tracing::error!("Can't bind thread to cpu");
                        return;
                    }
                }
                // finally run the main worker.
                // make sure things stay on this thread
                let tk_local = ::tokio::task::LocalSet::new();
                let _ = tk_local.block_on(
                    &th_tokio_rt,
                    Worker::new_and_loop(
                        th_config,
                        thread_id,
                        th_stop_working,
                        th_token_check,
                        th_socket_addrs,
                        work_recv,
                    ),
                );
            });
            loop {
                let queues_lock = match Arc::get_mut(&mut self._thread_work) {
                    Some(queues_lock) => queues_lock,
                    None => {
                        ::tokio::time::sleep(
                            ::std::time::Duration::from_millis(50),
                        )
                        .await;
                        continue;
                    }
                };
                queues_lock.push(work_send);
                break;
            }
            self._thread_pool.push(join_handle);
        }
        Ok(())
    }
}