#![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

use ::std::{net::SocketAddr, sync::Arc};
use ::tokio::{net::UdpSocket, task::JoinHandle};

mod config;
pub use config::Config;
pub mod dnssec;

/// Main fenrir library errors
#[derive(::thiserror::Error, Debug)]
pub enum Error {
    /// General I/O error
    #[error("IO: {0:?}")]
    IO(#[from] ::std::io::Error),
    /// Dnssec errors
    #[error("Dnssec: {0:?}")]
    Dnssec(#[from] dnssec::Error),
    /// The library was not initialized (run .start())
    #[error("not initialized")]
    NotInitialized,
}

/// Instance of a fenrir endpoint
#[allow(missing_copy_implementations, missing_debug_implementations)]
pub struct Fenrir {
    /// library Configuration
    cfg: Config,
    /// listening udp sockets
    sockets: Vec<(Arc<UdpSocket>, JoinHandle<::std::io::Result<()>>)>,
    /// DNSSEC resolver, with failovers
    dnssec: Option<dnssec::Dnssec>,
    /// Broadcast channel to tell workers to stop working
    stop_working: ::tokio::sync::broadcast::Sender<bool>,
}

// 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 listen_num = config.listen.len();
        let (sender, _) = ::tokio::sync::broadcast::channel(1);
        let endpoint = Fenrir {
            cfg: config.clone(),
            sockets: Vec::with_capacity(listen_num),
            dnssec: None,
            stop_working: sender,
        };
        Ok(endpoint)
    }
    /// Start all workers, listeners
    pub async fn start(&mut self) -> Result<(), Error> {
        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 mut toempty_socket = Vec::new();
        ::std::mem::swap(&mut self.sockets, &mut toempty_socket);
        let task = ::tokio::task::spawn(Self::stop_sockets(toempty_socket));
        let _ = ::futures::executor::block_on(task);
        self.dnssec = None;
    }
    /// Stop all workers, listeners
    pub async fn stop(&mut self) {
        let _ = self.stop_working.send(true);
        let mut toempty_socket = Vec::new();
        ::std::mem::swap(&mut self.sockets, &mut toempty_socket);
        Self::stop_sockets(toempty_socket).await;
        self.dnssec = None;
    }
    /// actually do the work of stopping resolvers and listeners
    async fn stop_sockets(
        sockets: Vec<(Arc<UdpSocket>, JoinHandle<::std::io::Result<()>>)>,
    ) {
        for s in sockets.into_iter() {
            let _ = s.1.await;
        }
    }
    /// Add all UDP sockets found in config
    /// and start listening for packets
    async fn add_sockets(&mut self) -> ::std::io::Result<()> {
        let sockets = self.cfg.listen.iter().map(|s_addr| async {
            let socket = ::tokio::spawn(bind_udp(s_addr.clone())).await??;
            Ok(Arc::new(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 join =
                        ::tokio::spawn(listen_udp(stop_working, s.clone()));
                    self.sockets.push((s, join));
                }
                Err(e) => {
                    return Err(e);
                }
            }
        }
        Ok(())
    }
    /// Get the raw TXT record of a Fenrir domain
    pub async fn resolv_str(&self, domain: &str) -> 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: &str) -> Result<dnssec::Record, Error> {
        let record_str = self.resolv_str(domain).await?;
        Ok(dnssec::Dnssec::parse_txt_record(&record_str)?)
    }
}

/// Add an async udp listener
async fn bind_udp(sock: SocketAddr) -> ::std::io::Result<UdpSocket> {
    let socket = UdpSocket::bind(sock).await?;
    // PERF: SO_REUSEADDR/REUSEPORT
    Ok(socket)
}

/// Run a dedicated loop to read packets on the listening socket
async fn listen_udp(
    mut stop_working: ::tokio::sync::broadcast::Receiver<bool>,
    socket: Arc<UdpSocket>,
) -> ::std::io::Result<()> {
    // jumbo frames are 9K max
    let mut buffer: [u8; 9000] = [0; 9000];
    loop {
        let (bytes, sock_from) = ::tokio::select! {
            _done = stop_working.recv() => {
                break;
            }
            result = socket.recv_from(&mut buffer) => {
                result?
            }
        };
        work(&buffer[0..bytes], sock_from).await;
    }
    Ok(())
}

/// Read and do stuff with the udp packet
async fn work(_buffer: &[u8], _sock_from: SocketAddr) {
    // Do nothing for now
}