pub mod bfd;
pub mod config;
pub mod control;
pub mod events;

use std::{
    fmt::{self, Display},
    net::IpAddr,
    sync::atomic::{AtomicU64, Ordering},
    time::{Duration, Instant},
};

use log::debug;
use nix::sys::socket::{getsockopt, setsockopt, sockopt};
use tokio::net::UdpSocket;

use crate::bfd::*;

/// A snapshot of the packet count and inter-packet interval statistics for one direction of a session.
#[derive(Debug, Clone, Copy, Default)]
pub struct IntervalStats {
    count: u64,
    min: Option<Duration>,
    max: Option<Duration>,
    mean: Option<Duration>,
}
impl IntervalStats {
    pub fn count(&self) -> u64 {
        self.count
    }
    pub fn min(&self) -> Option<Duration> {
        self.min
    }
    pub fn max(&self) -> Option<Duration> {
        self.max
    }
    pub fn mean(&self) -> Option<Duration> {
        self.mean
    }
}
impl Display for IntervalStats {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        let ms = |d: Option<Duration>| {
            d.map_or("-".to_string(), |d| {
                format!("{:.0}", d.as_secs_f64() * 1000.0)
            })
        };
        write!(
            f,
            "{} pkts, interval min/avg/max {}/{}/{} ms",
            self.count,
            ms(self.min),
            ms(self.mean),
            ms(self.max)
        )
    }
}

/// An optional `Instant` that can be shared between threads, stored as nanoseconds since its construction.
/// Instants earlier than the construction time are clamped to it.
#[derive(Debug)]
pub struct AtomicInstant {
    epoch: Instant,
    nanos: AtomicU64,
}
impl AtomicInstant {
    const NONE: u64 = u64::MAX;

    pub fn new() -> Self {
        Self {
            epoch: Instant::now(),
            nanos: AtomicU64::new(Self::NONE),
        }
    }
    pub fn load(&self) -> Option<Instant> {
        match self.nanos.load(Ordering::Relaxed) {
            Self::NONE => None,
            n => Some(self.epoch + Duration::from_nanos(n)),
        }
    }
    pub fn store(&self, value: Instant) {
        self.swap(value);
    }
    pub fn swap(&self, value: Instant) -> Option<Instant> {
        let n = u64::try_from(value.saturating_duration_since(self.epoch).as_nanos())
            .unwrap_or(Self::NONE - 1)
            .min(Self::NONE - 1);
        match self.nanos.swap(n, Ordering::Relaxed) {
            Self::NONE => None,
            prev => Some(self.epoch + Duration::from_nanos(prev)),
        }
    }
    pub fn clear(&self) {
        self.nanos.store(Self::NONE, Ordering::Relaxed);
    }
}
impl Default for AtomicInstant {
    fn default() -> Self {
        Self::new()
    }
}

/// Lock-free accumulator for packet counts and inter-packet intervals. Updates are not atomic as a group, so it
/// is intended for a single writer; a concurrent reader may observe a mix of old and new values.
#[derive(Debug)]
pub struct AtomicIntervalStats {
    count: AtomicU64,
    last: AtomicInstant,
    min_nanos: AtomicU64,
    max_nanos: AtomicU64,
    total_nanos: AtomicU64,
}
impl AtomicIntervalStats {
    pub fn new() -> Self {
        Self {
            count: AtomicU64::new(0),
            last: AtomicInstant::new(),
            min_nanos: AtomicU64::new(u64::MAX),
            max_nanos: AtomicU64::new(0),
            total_nanos: AtomicU64::new(0),
        }
    }
    pub fn record(&self, now: Instant) {
        self.count.fetch_add(1, Ordering::Relaxed);
        if let Some(prev) = self.last.swap(now) {
            let nanos =
                u64::try_from(now.saturating_duration_since(prev).as_nanos()).unwrap_or(u64::MAX);
            self.min_nanos.fetch_min(nanos, Ordering::Relaxed);
            self.max_nanos.fetch_max(nanos, Ordering::Relaxed);
            self.total_nanos.fetch_add(nanos, Ordering::Relaxed);
        }
    }
    pub fn reset(&self) {
        self.count.store(0, Ordering::Relaxed);
        self.last.clear();
        self.min_nanos.store(u64::MAX, Ordering::Relaxed);
        self.max_nanos.store(0, Ordering::Relaxed);
        self.total_nanos.store(0, Ordering::Relaxed);
    }
    pub fn snapshot(&self) -> IntervalStats {
        let count = self.count.load(Ordering::Relaxed);
        let intervals = count.saturating_sub(1);
        if intervals == 0 {
            return IntervalStats {
                count,
                ..Default::default()
            };
        }
        let total = self.total_nanos.load(Ordering::Relaxed);
        IntervalStats {
            count,
            min: Some(Duration::from_nanos(self.min_nanos.load(Ordering::Relaxed))),
            max: Some(Duration::from_nanos(self.max_nanos.load(Ordering::Relaxed))),
            mean: Some(Duration::from_nanos(total / intervals)),
        }
    }
}
impl Default for AtomicIntervalStats {
    fn default() -> Self {
        Self::new()
    }
}

fn fmt_ago(t: Option<Instant>) -> String {
    t.map_or("never".to_string(), |t| {
        format!("{}s ago", t.elapsed().as_secs())
    })
}

#[derive(Debug)]
pub struct BfdSessionStats {
    pub local_ip: IpAddr,
    pub remote_ip: IpAddr,
    pub local_discr: BfdDiscriminator,
    pub remote_discr: BfdDiscriminator,
    pub state: BfdState,
    pub last_diag: BfdDiagnostic,
    /// Packet statistics since the session last entered Up
    pub rx: IntervalStats,
    pub tx: IntervalStats,
    pub last_up: Option<Instant>,
    pub last_down: Option<Instant>,
    pub last_change: Instant,
    pub detect_time: BfdInterval,
    pub base_interval: BfdInterval,
}
impl BfdSessionStats {
    pub fn with_base_interval(mut self, base_interval: BfdInterval) -> Self {
        self.base_interval = base_interval;
        self
    }
}
impl Display for BfdSessionStats {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        writeln!(
            f,
            "{:<20} {:<9} {:>6} {:>6}",
            self.remote_ip,
            self.state,
            self.rx.count(),
            self.tx.count()
        )?;
        writeln!(
            f,
            "  LocalDiscr:{} RemoteDiscr:{} DetectTime: {} TxTime: {} Diag:{} Last: {}s",
            self.local_discr,
            self.remote_discr,
            self.detect_time,
            self.base_interval,
            self.last_diag,
            Instant::now().duration_since(self.last_change).as_secs()
        )?;
        writeln!(f, "  Rx: {}", self.rx)?;
        writeln!(f, "  Tx: {}", self.tx)?;
        write!(
            f,
            "  Last Up: {}  Last Down: {}",
            fmt_ago(self.last_up),
            fmt_ago(self.last_down)
        )
    }
}

pub fn set_ttl_or_hop_limit(sock: &UdpSocket, hop_limit: u8) -> Result<(), std::io::Error> {
    let addr = sock.local_addr()?;
    if addr.is_ipv4() {
        debug!("IPv4 socket, setting ttl {}", hop_limit as u32);
        sock.set_ttl(hop_limit as u32)
    } else if addr.is_ipv6() {
        debug!("IPv6 socket, setting hop limit {}", hop_limit as i32);
        let i32_hop_limit = hop_limit as i32;
        if let Err(e) = setsockopt(sock, sockopt::Ipv6Ttl, &i32_hop_limit) {
            Err(std::io::Error::from_raw_os_error(e as i32))
        } else {
            let res = getsockopt(sock, sockopt::Ipv6Ttl)?;
            debug!("Got {} after setting {}", res, i32_hop_limit);
            Ok(())
        }
    } else {
        panic!("UdpSocket with no address family ?!")
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn interval_stats_empty() {
        let s = AtomicIntervalStats::new().snapshot();
        assert_eq!(s.count(), 0);
        assert_eq!((s.min(), s.max(), s.mean()), (None, None, None));
    }

    #[test]
    fn interval_stats_single_packet_has_no_intervals() {
        let stats = AtomicIntervalStats::new();
        stats.record(Instant::now());
        let s = stats.snapshot();
        assert_eq!(s.count(), 1);
        assert_eq!((s.min(), s.max(), s.mean()), (None, None, None));
    }

    #[test]
    fn interval_stats_min_max_mean() {
        let stats = AtomicIntervalStats::new();
        let t0 = Instant::now();
        for ms in [0, 100, 400, 500] {
            stats.record(t0 + Duration::from_millis(ms));
        }
        let s = stats.snapshot();
        assert_eq!(s.count(), 4);
        assert_eq!(s.min(), Some(Duration::from_millis(100)));
        assert_eq!(s.max(), Some(Duration::from_millis(300)));
        assert_eq!(s.mean().unwrap().as_millis(), 166);
    }

    #[test]
    fn interval_stats_reset() {
        let stats = AtomicIntervalStats::new();
        let t0 = Instant::now();
        stats.record(t0);
        stats.record(t0 + Duration::from_millis(100));
        stats.reset();
        let s = stats.snapshot();
        assert_eq!(s.count(), 0);
        assert_eq!((s.min(), s.max(), s.mean()), (None, None, None));
        stats.record(t0 + Duration::from_millis(900));
        stats.record(t0 + Duration::from_millis(1000));
        assert_eq!(stats.snapshot().max(), Some(Duration::from_millis(100)));
    }

    #[test]
    fn atomic_instant_roundtrip() {
        let a = AtomicInstant::new();
        assert_eq!(a.load(), None);
        let t = Instant::now() + Duration::from_secs(5);
        assert_eq!(a.swap(t), None);
        assert_eq!(a.load(), Some(t));
        a.clear();
        assert_eq!(a.load(), None);
    }
}