//! Windows route-table inspection for protecting the relay path.
//!
//! The client binary uses this crate to keep Win32 route/metric calls out of
//! the relay session code. The crate can snapshot the current relay route and
//! install scoped route/interface overrides that are restored when dropped.

use std::net::IpAddr;

#[cfg(not(windows))]
use anyhow::{Result, bail};

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct RouteSnapshot {
    destination: IpAddr,
    source: IpAddr,
    next_hop: Option<IpAddr>,
    route_prefix: IpAddr,
    route_prefix_len: u8,
    interface_index: u32,
    interface_luid: u64,
    metric: u32,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct NetworkInterfaceIdentity {
    index: u32,
    luid: u64,
}

impl NetworkInterfaceIdentity {
    #[cfg_attr(not(windows), allow(dead_code))]
    const fn new(index: u32, luid: u64) -> Self {
        Self { index, luid }
    }

    #[must_use]
    pub const fn index(self) -> u32 {
        self.index
    }

    #[must_use]
    pub const fn luid(self) -> u64 {
        self.luid
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum IpInterfaceFamily {
    Ipv4,
    Ipv6,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct InterfaceMetricSnapshot {
    identity: NetworkInterfaceIdentity,
    family: IpInterfaceFamily,
    automatic_metric: bool,
    metric: u32,
    disable_default_routes: bool,
}

impl InterfaceMetricSnapshot {
    #[cfg_attr(not(windows), allow(dead_code))]
    const fn new(
        identity: NetworkInterfaceIdentity,
        family: IpInterfaceFamily,
        automatic_metric: bool,
        metric: u32,
        disable_default_routes: bool,
    ) -> Self {
        Self {
            identity,
            family,
            automatic_metric,
            metric,
            disable_default_routes,
        }
    }

    #[must_use]
    pub const fn identity(self) -> NetworkInterfaceIdentity {
        self.identity
    }

    #[must_use]
    pub const fn family(self) -> IpInterfaceFamily {
        self.family
    }

    #[must_use]
    pub const fn automatic_metric(self) -> bool {
        self.automatic_metric
    }

    #[must_use]
    pub const fn metric(self) -> u32 {
        self.metric
    }

    #[must_use]
    pub const fn disable_default_routes(self) -> bool {
        self.disable_default_routes
    }
}

impl RouteSnapshot {
    #[cfg_attr(not(windows), allow(dead_code))]
    #[allow(clippy::too_many_arguments)]
    const fn new(
        destination: IpAddr,
        source: IpAddr,
        next_hop: Option<IpAddr>,
        route_prefix: IpAddr,
        route_prefix_len: u8,
        interface_index: u32,
        interface_luid: u64,
        metric: u32,
    ) -> Self {
        Self {
            destination,
            source,
            next_hop,
            route_prefix,
            route_prefix_len,
            interface_index,
            interface_luid,
            metric,
        }
    }

    #[must_use]
    pub const fn destination(&self) -> IpAddr {
        self.destination
    }

    #[must_use]
    pub const fn source(&self) -> IpAddr {
        self.source
    }

    #[must_use]
    pub const fn next_hop(&self) -> Option<IpAddr> {
        self.next_hop
    }

    #[must_use]
    pub const fn route_prefix(&self) -> IpAddr {
        self.route_prefix
    }

    #[must_use]
    pub const fn route_prefix_len(&self) -> u8 {
        self.route_prefix_len
    }

    #[must_use]
    pub const fn interface_index(&self) -> u32 {
        self.interface_index
    }

    #[must_use]
    pub const fn interface_luid(&self) -> u64 {
        self.interface_luid
    }

    #[must_use]
    pub const fn interface_identity(&self) -> NetworkInterfaceIdentity {
        NetworkInterfaceIdentity::new(self.interface_index, self.interface_luid)
    }

    #[must_use]
    pub const fn metric(&self) -> u32 {
        self.metric
    }

    #[must_use]
    pub fn is_host_route_to(&self, destination: IpAddr) -> bool {
        self.route_prefix == destination && self.route_prefix_len == host_prefix_len(destination)
    }
}

const fn host_prefix_len(destination: IpAddr) -> u8 {
    match destination {
        IpAddr::V4(_) => 32,
        IpAddr::V6(_) => 128,
    }
}

#[cfg(windows)]
mod windows;

#[cfg(windows)]
pub use windows::{PinnedRelayRoute, best_route_to, interface_identity_from_guid, pin_relay_route};
#[cfg(windows)]
pub use windows::{
    ScopedDefaultRoutes, ScopedInterfaceMetric, interface_metric,
    set_scoped_default_routes_disabled, set_scoped_interface_metric,
};

#[cfg(not(windows))]
pub fn best_route_to(_destination: IpAddr) -> Result<RouteSnapshot> {
    bail!("Windows route inspection is only available on Windows");
}

#[cfg(not(windows))]
#[derive(Debug)]
pub struct PinnedRelayRoute {
    _private: (),
}

#[cfg(not(windows))]
pub fn pin_relay_route(_route: &RouteSnapshot) -> Result<PinnedRelayRoute> {
    bail!("Windows route pinning is only available on Windows");
}

#[cfg(not(windows))]
pub fn interface_identity_from_guid(_interface_guid: &str) -> Result<NetworkInterfaceIdentity> {
    bail!("Windows interface identity lookup is only available on Windows");
}

#[cfg(not(windows))]
#[derive(Debug)]
pub struct ScopedInterfaceMetric {
    _private: (),
}

#[cfg(not(windows))]
pub fn interface_metric(
    _identity: NetworkInterfaceIdentity,
    _family: IpInterfaceFamily,
) -> Result<InterfaceMetricSnapshot> {
    bail!("Windows interface metric lookup is only available on Windows");
}

#[cfg(not(windows))]
pub fn set_scoped_interface_metric(
    _identity: NetworkInterfaceIdentity,
    _family: IpInterfaceFamily,
    _metric: u32,
) -> Result<ScopedInterfaceMetric> {
    bail!("Windows interface metric updates are only available on Windows");
}

#[cfg(not(windows))]
#[derive(Debug)]
pub struct ScopedDefaultRoutes {
    _private: (),
}

#[cfg(not(windows))]
pub fn set_scoped_default_routes_disabled(
    _identity: NetworkInterfaceIdentity,
    _family: IpInterfaceFamily,
    _disabled: bool,
) -> Result<ScopedDefaultRoutes> {
    bail!("Windows interface default-route updates are only available on Windows");
}

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

    #[test]
    fn exposes_route_snapshot_fields() {
        let snapshot = RouteSnapshot::new(
            ip("203.0.113.10"),
            ip("192.0.2.44"),
            Some(ip("192.0.2.1")),
            ip("0.0.0.0"),
            0,
            12,
            34,
            25,
        );

        assert_eq!(snapshot.destination(), ip("203.0.113.10"));
        assert_eq!(snapshot.source(), ip("192.0.2.44"));
        assert_eq!(snapshot.next_hop(), Some(ip("192.0.2.1")));
        assert_eq!(snapshot.route_prefix(), ip("0.0.0.0"));
        assert_eq!(snapshot.route_prefix_len(), 0);
        assert_eq!(snapshot.interface_index(), 12);
        assert_eq!(snapshot.interface_luid(), 34);
        assert_eq!(
            snapshot.interface_identity(),
            NetworkInterfaceIdentity::new(12, 34)
        );
        assert_eq!(snapshot.metric(), 25);
        assert!(!snapshot.is_host_route_to(ip("203.0.113.10")));
    }

    #[test]
    fn identifies_host_routes_to_destination() {
        let snapshot = RouteSnapshot::new(
            ip("203.0.113.10"),
            ip("192.0.2.44"),
            Some(ip("192.0.2.1")),
            ip("203.0.113.10"),
            32,
            12,
            34,
            0,
        );
        assert!(snapshot.is_host_route_to(ip("203.0.113.10")));
        assert!(!snapshot.is_host_route_to(ip("203.0.113.11")));

        let snapshot = RouteSnapshot::new(
            ip("2001:db8::10"),
            ip("2001:db8::44"),
            None,
            ip("2001:db8::10"),
            128,
            12,
            34,
            0,
        );
        assert!(snapshot.is_host_route_to(ip("2001:db8::10")));
    }

    #[test]
    fn exposes_network_interface_identity_fields() {
        let identity = NetworkInterfaceIdentity::new(12, 34);

        assert_eq!(identity.index(), 12);
        assert_eq!(identity.luid(), 34);
    }

    #[test]
    fn exposes_interface_metric_snapshot_fields() {
        let identity = NetworkInterfaceIdentity::new(12, 34);
        let snapshot =
            InterfaceMetricSnapshot::new(identity, IpInterfaceFamily::Ipv4, true, 25, false);

        assert_eq!(snapshot.identity(), identity);
        assert_eq!(snapshot.family(), IpInterfaceFamily::Ipv4);
        assert!(snapshot.automatic_metric());
        assert_eq!(snapshot.metric(), 25);
        assert!(!snapshot.disable_default_routes());
    }

    #[cfg(not(windows))]
    #[test]
    fn rejects_route_inspection_on_non_windows() {
        assert!(best_route_to(ip("203.0.113.10")).is_err());
    }

    #[cfg(not(windows))]
    #[test]
    fn rejects_route_pinning_on_non_windows() {
        let snapshot = RouteSnapshot::new(
            ip("203.0.113.10"),
            ip("192.0.2.44"),
            Some(ip("192.0.2.1")),
            ip("0.0.0.0"),
            0,
            12,
            34,
            25,
        );

        assert!(pin_relay_route(&snapshot).is_err());
    }

    #[cfg(not(windows))]
    #[test]
    fn rejects_interface_lookup_on_non_windows() {
        assert!(interface_identity_from_guid("{00112233-4455-6677-8899-AABBCCDDEEFF}").is_err());
    }

    #[cfg(not(windows))]
    #[test]
    fn rejects_interface_metric_operations_on_non_windows() {
        let identity = NetworkInterfaceIdentity::new(12, 34);

        assert!(interface_metric(identity, IpInterfaceFamily::Ipv4).is_err());
        assert!(set_scoped_interface_metric(identity, IpInterfaceFamily::Ipv4, 500).is_err());
        assert!(
            set_scoped_default_routes_disabled(identity, IpInterfaceFamily::Ipv4, true).is_err()
        );
    }

    fn ip(value: &str) -> IpAddr {
        value.parse().unwrap()
    }
}