use std::{fs, net::SocketAddr, path::PathBuf};
#[cfg(windows)]
use std::{
    sync::{Arc, mpsc},
    thread,
    time::Duration,
};

use anyhow::{Context, Result, bail};
use clap::Parser;
#[cfg(windows)]
use lanparty_client_core::ClientRelayIo;
use lanparty_client_core::{
    ClientIdentity, ClientIdentityStore, ClientSession, ClientSessionConfig, connect_client,
};
#[cfg(windows)]
use lanparty_client_route::{
    IpInterfaceFamily, NetworkInterfaceIdentity, PinnedRelayRoute, RouteSnapshot,
    ScopedDefaultRoutes, ScopedInterfaceMetric, ScopedInterfaceMtu,
};
#[cfg(windows)]
use lanparty_client_tap::TapAdapter;
use lanparty_ctrl::RoomCode;
use lanparty_proto::MacAddr;

#[cfg(windows)]
const TAP_INTERFACE_METRIC: u32 = 9_000;
#[cfg(windows)]
const RELAY_ROUTE_VERIFY_INTERVAL: Duration = Duration::from_secs(5);

#[derive(Debug, Parser)]
#[command(
    name = "lanparty-client-win",
    about = "Windows TAP client for the LAN party L2 tunnel"
)]
struct ClientArgs {
    /// Relay UDP socket address, for example 203.0.113.10:443.
    #[arg(long)]
    relay: SocketAddr,

    /// TLS server name expected in the relay certificate.
    #[arg(long, default_value = "lanparty-relay.local")]
    server_name: String,

    /// DER-encoded relay CA/certificate to trust.
    #[arg(long, value_name = "PATH")]
    relay_ca_cert: PathBuf,

    /// Room code to join as a remote client.
    #[arg(long)]
    room: RoomCode,

    /// Identity JSON file used to persist the generated virtual MAC.
    #[arg(
        long = "identity-file",
        value_name = "PATH",
        default_value = "lanparty-client-identity.json"
    )]
    identity_file: PathBuf,

    /// Override the generated locally administered TAP MAC address.
    #[arg(long)]
    virtual_mac: Option<MacAddr>,

    /// Client's advertised QUIC datagram budget before relay clamping.
    #[arg(long, default_value_t = 1400)]
    max_datagram_size: u16,
}

impl ClientArgs {
    fn into_config(self) -> Result<ClientSessionConfig> {
        let relay_ca_cert = fs::read(&self.relay_ca_cert).with_context(|| {
            format!(
                "failed to read relay CA certificate {}",
                self.relay_ca_cert.display()
            )
        })?;

        let identity = match self.virtual_mac {
            Some(virtual_mac) => ClientIdentity::new(virtual_mac)?,
            None => ClientIdentityStore::new(self.identity_file)?.load_or_create()?,
        };

        ClientSessionConfig::new(
            self.relay,
            self.server_name,
            relay_ca_cert,
            self.room,
            identity.virtual_mac(),
            self.max_datagram_size,
        )
    }
}

#[tokio::main]
async fn main() -> Result<()> {
    let config = ClientArgs::parse().into_config()?;
    println!(
        "lanparty-client-win connecting virtual MAC {} to relay {} room {}",
        config.virtual_mac(),
        config.relay_addr(),
        config.room()
    );

    let session = connect_client(config).await?;
    println!(
        "lanparty-client-win connected as peer {} in room id {} with TAP MTU {}",
        session.welcome().peer_id(),
        session.welcome().room_id(),
        session.welcome().effective_tap_mtu()
    );
    #[cfg(windows)]
    let relay_route_pin = match pin_relay_route_before_tap(session.config().relay_addr().ip()) {
        Ok(pin) => pin,
        Err(error) => {
            session.shutdown("client startup failed").await;
            return Err(error);
        }
    };
    #[cfg(windows)]
    let run_result = run_client(&session, &relay_route_pin).await;
    #[cfg(not(windows))]
    let run_result = run_client(&session).await;
    session.shutdown("client shutting down").await;
    #[cfg(windows)]
    drop(relay_route_pin);

    run_result
}

#[cfg(windows)]
async fn run_client(session: &ClientSession, relay_route_pin: &PinnedRelayRoute) -> Result<()> {
    let OpenedTapAdapter { tap, _route_guard } = open_tap_adapter(session)?;
    let relay_route =
        verify_relay_route_is_pinned(session.config().relay_addr().ip(), relay_route_pin)
            .context("relay route changed after TAP activation")?;
    print_verified_relay_route(&relay_route);
    println!(
        "bridging TAP frames; relay route is pinned and TAP route policy is scoped; press Ctrl-C to stop"
    );

    let frame_pump = run_tap_frame_pump(session.relay_io(), tap);
    tokio::pin!(frame_pump);
    let shutdown = tokio::signal::ctrl_c();
    tokio::pin!(shutdown);
    let mut relay_route_check = tokio::time::interval_at(
        tokio::time::Instant::now() + RELAY_ROUTE_VERIFY_INTERVAL,
        RELAY_ROUTE_VERIFY_INTERVAL,
    );
    relay_route_check.set_missed_tick_behavior(tokio::time::MissedTickBehavior::Delay);

    loop {
        tokio::select! {
            result = &mut frame_pump => return result,
            result = &mut shutdown => return result.context("failed to wait for Ctrl-C"),
            _ = relay_route_check.tick() => {
                verify_relay_route_is_pinned(
                    session.config().relay_addr().ip(),
                    relay_route_pin,
                )
                .context("relay route changed while bridging")?;
            }
        }
    }
}

#[cfg(not(windows))]
async fn run_client(session: &ClientSession) -> Result<()> {
    open_tap_adapter(session);
    println!("TAP frame pump and route pinning are not wired yet; press Ctrl-C to stop");

    tokio::signal::ctrl_c()
        .await
        .context("failed to wait for Ctrl-C")
}

#[cfg(windows)]
fn pin_relay_route_before_tap(destination: std::net::IpAddr) -> Result<PinnedRelayRoute> {
    let route = lanparty_client_route::best_route_to(destination)
        .context("failed to inspect relay route before TAP activation")?;
    print_relay_route(&route);
    let pin = lanparty_client_route::pin_relay_route(&route)
        .context("failed to pin relay route before TAP activation")?;
    print_pinned_relay_route(&pin);

    Ok(pin)
}

#[cfg(windows)]
fn print_relay_route(route: &RouteSnapshot) {
    println!(
        "relay route before TAP: destination {} source {} next hop {} interface index {} LUID {} prefix {}/{} metric {}",
        route.destination(),
        route.source(),
        route
            .next_hop()
            .map_or_else(|| "on-link".to_string(), |next_hop| next_hop.to_string()),
        route.interface_index(),
        route.interface_luid(),
        route.route_prefix(),
        route.route_prefix_len(),
        route.metric()
    );
}

#[cfg(windows)]
fn print_pinned_relay_route(route: &PinnedRelayRoute) {
    println!(
        "relay route pinned before TAP: destination {} next hop {} interface index {} LUID {}",
        route.destination(),
        route
            .next_hop()
            .map_or_else(|| "on-link".to_string(), |next_hop| next_hop.to_string()),
        route.interface_index(),
        route.interface_luid()
    );
}

#[cfg(windows)]
fn verify_relay_route_is_pinned(
    destination: std::net::IpAddr,
    pin: &PinnedRelayRoute,
) -> Result<RouteSnapshot> {
    let route = lanparty_client_route::best_route_to(destination)
        .context("failed to inspect relay route")?;
    if !relay_route_matches_pin(&route, pin) {
        bail!(
            "relay route to {} uses prefix {}/{} next hop {} interface index {} LUID {}, expected pinned host route via next hop {} interface index {} LUID {}",
            route.destination(),
            route.route_prefix(),
            route.route_prefix_len(),
            route_next_hop_label(route.next_hop()),
            route.interface_index(),
            route.interface_luid(),
            route_next_hop_label(pin.next_hop()),
            pin.interface_index(),
            pin.interface_luid(),
        );
    }

    Ok(route)
}

#[cfg(windows)]
fn relay_route_matches_pin(route: &RouteSnapshot, pin: &PinnedRelayRoute) -> bool {
    route.destination() == pin.destination()
        && route.is_host_route_to(pin.destination())
        && route.next_hop() == pin.next_hop()
        && route.interface_index() == pin.interface_index()
        && route.interface_luid() == pin.interface_luid()
}

#[cfg(windows)]
fn print_verified_relay_route(route: &RouteSnapshot) {
    println!(
        "relay route verified after TAP activation: destination {} next hop {} interface index {} LUID {} prefix {}/{} metric {}",
        route.destination(),
        route_next_hop_label(route.next_hop()),
        route.interface_index(),
        route.interface_luid(),
        route.route_prefix(),
        route.route_prefix_len(),
        route.metric()
    );
}

#[cfg(windows)]
fn route_next_hop_label(next_hop: Option<std::net::IpAddr>) -> String {
    next_hop.map_or_else(|| "on-link".to_string(), |next_hop| next_hop.to_string())
}

#[cfg(windows)]
struct OpenedTapAdapter {
    tap: TapAdapter,
    _route_guard: TapRouteProtectionGuard,
}

#[cfg(windows)]
struct TapRouteProtectionGuard {
    _ipv4_metric: ScopedInterfaceMetric,
    _ipv4_default_routes: ScopedDefaultRoutes,
    _ipv4_mtu: ScopedInterfaceMtu,
    _ipv6_metric: Option<ScopedInterfaceMetric>,
    _ipv6_default_routes: Option<ScopedDefaultRoutes>,
    _ipv6_mtu: Option<ScopedInterfaceMtu>,
}

#[cfg(windows)]
fn open_tap_adapter(session: &ClientSession) -> Result<OpenedTapAdapter> {
    let tap = lanparty_client_tap::open_first_adapter()?;
    let tap_interface =
        lanparty_client_route::interface_identity_from_guid(tap.info().instance_id())
            .context("failed to resolve TAP interface identity")?;
    let route_guard = protect_tap_routes(tap_interface, session.welcome().effective_tap_mtu())?;
    let driver_mac = tap.driver_mac()?;
    let driver_mtu = tap.driver_mtu()?;
    validate_tap_driver_mac(session.config().virtual_mac(), driver_mac)?;
    tap.set_media_connected(true)?;

    println!(
        "lanparty-client-win opened TAP adapter {}",
        tap.info().device_path()
    );
    println!(
        "TAP driver reports MAC {} and MTU {}; relay selected TAP MTU {}",
        driver_mac,
        driver_mtu,
        session.welcome().effective_tap_mtu()
    );
    println!(
        "TAP interface index {} LUID {}",
        tap_interface.index(),
        tap_interface.luid()
    );

    Ok(OpenedTapAdapter {
        tap,
        _route_guard: route_guard,
    })
}

#[cfg_attr(not(windows), allow(dead_code))]
fn validate_tap_driver_mac(expected_mac: MacAddr, driver_mac: MacAddr) -> Result<()> {
    if driver_mac != expected_mac {
        bail!(
            "TAP driver MAC {driver_mac} does not match tunnel identity {expected_mac}; automatic MAC configuration is not wired yet"
        );
    }

    Ok(())
}

#[cfg(windows)]
fn protect_tap_routes(
    identity: NetworkInterfaceIdentity,
    tap_mtu: u16,
) -> Result<TapRouteProtectionGuard> {
    let tap_mtu = u32::from(tap_mtu);
    let ipv4_mtu =
        lanparty_client_route::set_scoped_interface_mtu(identity, IpInterfaceFamily::Ipv4, tap_mtu)
            .context("failed to set TAP IPv4 MTU")?;
    print_tap_mtu_override(IpInterfaceFamily::Ipv4, tap_mtu, &ipv4_mtu);

    let ipv4_metric = lanparty_client_route::set_scoped_interface_metric(
        identity,
        IpInterfaceFamily::Ipv4,
        TAP_INTERFACE_METRIC,
    )
    .context("failed to set TAP IPv4 interface metric")?;
    print_tap_metric_override(IpInterfaceFamily::Ipv4, &ipv4_metric);

    let ipv4_default_routes = lanparty_client_route::set_scoped_default_routes_disabled(
        identity,
        IpInterfaceFamily::Ipv4,
        true,
    )
    .context("failed to disable TAP IPv4 default routes")?;
    print_tap_default_routes_override(IpInterfaceFamily::Ipv4, &ipv4_default_routes);

    let ipv6_mtu = match lanparty_client_route::set_scoped_interface_mtu(
        identity,
        IpInterfaceFamily::Ipv6,
        tap_mtu,
    ) {
        Ok(mtu) => {
            print_tap_mtu_override(IpInterfaceFamily::Ipv6, tap_mtu, &mtu);
            Some(mtu)
        }
        Err(error) => {
            eprintln!("failed to set TAP IPv6 MTU; IPv6 may use the previous MTU: {error:#}");
            None
        }
    };

    let ipv6_metric = match lanparty_client_route::set_scoped_interface_metric(
        identity,
        IpInterfaceFamily::Ipv6,
        TAP_INTERFACE_METRIC,
    ) {
        Ok(metric) => {
            print_tap_metric_override(IpInterfaceFamily::Ipv6, &metric);
            Some(metric)
        }
        Err(error) => {
            eprintln!(
                "failed to set TAP IPv6 interface metric; IPv6 route protection may be incomplete: {error:#}"
            );
            None
        }
    };

    let ipv6_default_routes = match lanparty_client_route::set_scoped_default_routes_disabled(
        identity,
        IpInterfaceFamily::Ipv6,
        true,
    ) {
        Ok(default_routes) => {
            print_tap_default_routes_override(IpInterfaceFamily::Ipv6, &default_routes);
            Some(default_routes)
        }
        Err(error) => {
            eprintln!(
                "failed to disable TAP IPv6 default routes; IPv6 route protection may be incomplete: {error:#}"
            );
            None
        }
    };

    Ok(TapRouteProtectionGuard {
        _ipv4_metric: ipv4_metric,
        _ipv4_default_routes: ipv4_default_routes,
        _ipv4_mtu: ipv4_mtu,
        _ipv6_metric: ipv6_metric,
        _ipv6_default_routes: ipv6_default_routes,
        _ipv6_mtu: ipv6_mtu,
    })
}

#[cfg(windows)]
fn print_tap_mtu_override(family: IpInterfaceFamily, mtu: u32, guard: &ScopedInterfaceMtu) {
    let previous = guard.previous();
    println!(
        "TAP {family:?} MTU set to {mtu}; previous MTU {}",
        previous.mtu()
    );
}

#[cfg(windows)]
fn print_tap_metric_override(family: IpInterfaceFamily, metric: &ScopedInterfaceMetric) {
    let previous = metric.previous();
    println!(
        "TAP {family:?} interface metric set to {TAP_INTERFACE_METRIC}; previous metric {} automatic {} default-routes-disabled {}",
        previous.metric(),
        previous.automatic_metric(),
        previous.disable_default_routes()
    );
}

#[cfg(windows)]
fn print_tap_default_routes_override(family: IpInterfaceFamily, routes: &ScopedDefaultRoutes) {
    let previous = routes.previous();
    println!(
        "TAP {family:?} default routes disabled; previous default-routes-disabled {}",
        previous.disable_default_routes()
    );
}

#[cfg(windows)]
async fn run_tap_frame_pump(relay_io: ClientRelayIo, tap: TapAdapter) -> Result<()> {
    let tap = Arc::new(tap);
    let (tap_error_tx, tap_error_rx) = mpsc::channel();
    spawn_tap_reader(Arc::clone(&tap), relay_io.clone(), tap_error_tx)?;

    let tap_reader_error = tokio::task::spawn_blocking(move || tap_error_rx.recv());
    tokio::pin!(tap_reader_error);

    loop {
        tokio::select! {
            reader_result = &mut tap_reader_error => {
                let reader_result = reader_result.context("TAP reader error watcher panicked")?;
                let error = reader_result
                    .context("TAP reader thread stopped without reporting an error")?;
                return Err::<(), _>(error).context("TAP reader thread stopped");
            }
            relay_frame = relay_io.recv_ethernet() => {
                let relay_frame = relay_frame.context("failed to receive relay Ethernet frame")?;
                let tap = Arc::clone(&tap);
                let payload = relay_frame.payload().to_vec();
                tokio::task::spawn_blocking(move || {
                    tap.write_ethernet_frame(&payload)
                        .context("failed to write relay Ethernet frame to TAP")
                })
                .await
                .context("TAP writer task panicked")??;
            }
        }
    }
}

#[cfg(windows)]
fn spawn_tap_reader(
    tap: Arc<TapAdapter>,
    relay_io: ClientRelayIo,
    tap_error_tx: mpsc::Sender<anyhow::Error>,
) -> Result<()> {
    thread::Builder::new()
        .name("lanparty-tap-reader".to_string())
        .spawn(move || {
            let mut buffer = vec![0_u8; lanparty_client_tap::TAP_FRAME_BUFFER_LEN];
            loop {
                let result = read_and_relay_tap_frame(&tap, &relay_io, &mut buffer);
                if let Err(error) = result {
                    let _ = tap_error_tx.send(error);
                    return;
                }
            }
        })
        .context("failed to spawn TAP reader thread")?;

    Ok(())
}

#[cfg(windows)]
fn read_and_relay_tap_frame(
    tap: &TapAdapter,
    relay_io: &ClientRelayIo,
    buffer: &mut [u8],
) -> Result<()> {
    let len = tap
        .read_ethernet_frame(buffer)
        .context("failed to read TAP Ethernet frame")?;
    relay_io
        .send_ethernet(&buffer[..len])
        .context("failed to send TAP Ethernet frame to relay")?;

    Ok(())
}

#[cfg(not(windows))]
fn open_tap_adapter(_session: &ClientSession) {
    println!("Windows TAP adapter opening is compiled only on Windows");
}

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

    #[test]
    fn accepts_matching_tap_driver_mac() {
        assert!(validate_tap_driver_mac(mac(1), mac(1)).is_ok());
    }

    #[test]
    fn rejects_tap_driver_mac_mismatch() {
        let error = validate_tap_driver_mac(mac(1), mac(2)).unwrap_err();

        assert!(error.to_string().contains("does not match tunnel identity"));
    }

    const fn mac(last_octet: u8) -> MacAddr {
        MacAddr::new([0x02, 0, 0, 0, 0, last_octet])
    }
}