use crate::network::{ConnEvent, NetError, NetworkTransport};
use async_trait::async_trait;
use bytes::Bytes;
use iroh::endpoint::{Connection, ConnectionError, VarInt};
use iroh::{Endpoint, EndpointId};
use std::collections::{HashMap, HashSet};
use std::sync::{Arc, Mutex as StdMutex};
use std::time::Duration;
use tokio::sync::mpsc;
use tokio::sync::mpsc::Receiver;

use crate::files::{AttachmentId, ChatAttachment};
use crate::protocol::{AUDIO_ALPN, FILES_ALPN};

/// Per-peer datagram send queue depth. Audio is real-time, so a backlog is
/// useless latency — keep it shallow and drop the oldest frame when full.
const SEND_QUEUE_DEPTH: usize = 8;

/// How many inbound connections we'll buffer for a single peer's supervisor.
/// During a healthy link the supervisor drains this promptly; a small buffer
/// just covers the brief window between detecting a drop and re-awaiting.
const INBOUND_QUEUE_DEPTH: usize = 4;

/// Reconnect backoff bounds for the dialing side. Starts gentle so a momentary
/// blip recovers almost instantly, and caps so a long outage doesn't hammer.
const INITIAL_BACKOFF: Duration = Duration::from_millis(250);
const MAX_BACKOFF: Duration = Duration::from_secs(5);

/// QUIC application error code sent when we leave/quit intentionally, so the
/// remote supervisor can tell a graceful departure from a transient drop. The
/// specific value is informational; any *application* close (vs a timeout/reset)
/// already means "the peer closed this on purpose."
const GOODBYE_CODE: u32 = 1;

/// Bound on each phase (connect, read) of a chat-attachment fetch, so a slow or
/// stalled sender can't hang the fetch indefinitely.
const FILE_FETCH_TIMEOUT: Duration = Duration::from_secs(30);

/// State shared between the transport, its protocol handler, and every per-peer
/// supervisor task. One supervisor owns a peer's whole connection lifecycle.
struct Shared {
    /// Used by dialer-side supervisors to (re)establish connections.
    endpoint: Endpoint,
    self_id: EndpointId,
    /// Sync-lockable send handles, so `broadcast` can fan out from the (non-async)
    /// capture/encode thread without touching the Tokio runtime. A supervisor
    /// inserts its handle when a link comes up and removes it when the link dies,
    /// so `broadcast` only ever targets peers that are currently reachable.
    senders: StdMutex<HashMap<EndpointId, mpsc::Sender<Bytes>>>,
    /// Last-known full address (relay + direct addrs) per peer, retained for the
    /// supervisor's lifetime and refreshed whenever the peer (re)announces. The
    /// dialer dials this directly so a reconnect never depends on the address
    /// lookup, which a transient gossip `Leave`/`NeighborDown` can purge — the
    /// bug that left the dialer redial-looping with "no address" forever.
    addrs: StdMutex<HashMap<EndpointId, iroh::EndpointAddr>>,
    /// One supervisor task per known peer.
    peers: tokio::sync::Mutex<HashMap<EndpointId, PeerHandle>>,
    /// The currently-live connection per peer, tracked so an intentional leave
    /// can explicitly close each one with [`GOODBYE_CODE`] (a prompt, reliable
    /// "I'm leaving" signal the remote can distinguish from a network drop). A
    /// supervisor inserts its connection when the link comes up and removes it
    /// when the link dies.
    live_conns: StdMutex<HashMap<EndpointId, Connection>>,
    /// Core-owned audio admission snapshot for this room session. It mirrors the
    /// verified gossip roster plus peers still inside reconnect grace; transport
    /// connections alone never mutate this set.
    admitted_audio: StdMutex<HashSet<EndpointId>>,
    /// Chat file attachments we're serving to room members this session, keyed by
    /// the random attachment id. Populated when we send a chat file; read by the
    /// file protocol handler to answer a member's fetch. Cleared on leave. Each
    /// blob is already byte-capped at send time.
    /// Blobs we serve to room members, bounded by count and byte budgets
    /// (Phase 3C) — an evicted id reads as "sender no longer has the file".
    served_files: StdMutex<crate::files::ServeStore>,
    incoming_tx: mpsc::Sender<(EndpointId, Bytes)>,
    /// Best-effort link-state notifications for the UI (connecting / connected).
    conn_events_tx: mpsc::Sender<ConnEvent>,
}

struct PeerHandle {
    /// The supervisor owning this peer's connect → run → reconnect loop.
    supervisor: tokio::task::JoinHandle<()>,
    /// Inbound connections accepted for this peer are routed here so the
    /// acceptor-side supervisor can pick them up (initial and reconnect).
    inbound_tx: mpsc::Sender<Connection>,
}

/// Aborts a spawned task when dropped. The supervisor holds its send/read loops
/// in these so that cancelling the supervisor (via `remove`'s `abort`) tears the
/// loops down too — otherwise they'd keep their `Connection` clones alive and
/// the link would never actually close.
struct AbortOnDrop(tokio::task::JoinHandle<()>);

impl Drop for AbortOnDrop {
    fn drop(&mut self) {
        self.0.abort();
    }
}

impl Shared {
    /// Ensure a supervisor task exists for `peer_id`, returning its inbound
    /// connection sender. Idempotent: a second call for a known peer just hands
    /// back the existing sender. Both the reactive `connect_peer` path and the
    /// inbound `accept()` path funnel through here, so whichever fires first
    /// spins the peer up and the roles stay deterministic by id.
    async fn ensure_supervisor(self: &Arc<Self>, peer_id: EndpointId) -> mpsc::Sender<Connection> {
        let mut peers = self.peers.lock().await;
        if let Some(handle) = peers.get(&peer_id) {
            return handle.inbound_tx.clone();
        }

        let (inbound_tx, inbound_rx) = mpsc::channel::<Connection>(INBOUND_QUEUE_DEPTH);
        let shared = self.clone();
        let supervisor = tokio::spawn(supervise(shared, peer_id, inbound_rx));
        let inbound_tx_ret = inbound_tx.clone();
        peers.insert(
            peer_id,
            PeerHandle {
                supervisor,
                inbound_tx,
            },
        );
        crate::log_msg(&format!("Transport: supervising peer {:?}", peer_id));
        inbound_tx_ret
    }

    /// Permanently retire a peer (it left the room). Stops its supervisor — which
    /// cancels any in-flight dial or live link — and drops its send handle.
    async fn remove(&self, peer_id: EndpointId) {
        self.senders.lock().unwrap().remove(&peer_id);
        self.addrs.lock().unwrap().remove(&peer_id);
        if let Some(handle) = self.peers.lock().await.remove(&peer_id) {
            handle.supervisor.abort();
            crate::log_msg(&format!(
                "Transport: stopped supervising peer {:?}",
                peer_id
            ));
        }
    }

    fn audio_sender_admitted(&self, peer_id: EndpointId) -> bool {
        let roster = self.admitted_audio.lock().unwrap();
        audio_sender_admitted(peer_id, &roster)
    }

    fn apply_audio_admission(&self, peer_id: EndpointId, event: AudioAdmissionEvent) {
        let mut roster = self.admitted_audio.lock().unwrap();
        apply_audio_admission_event(&mut roster, peer_id, event);
    }
}

/// Why a peer's live-link wait woke up.
enum Wake {
    /// The QUIC connection closed; the error says how. An *application* close
    /// means the peer left on purpose (reconnect would be wrong); a timeout/reset
    /// is a transient drop we should reconnect through.
    Closed(ConnectionError),
    /// A fresh inbound connection arrived (acceptor side) — switch to it.
    Replacement(Connection),
    /// The peer was retired; tear down.
    Shutdown,
}

/// True when the peer closed the connection with our [`GOODBYE_CODE`] — i.e. an
/// intentional leave/quit via [`IrohTransport::leave`]. Any other close (idle
/// timeout, reset, or an application close with a different code) is treated as a
/// transient drop to reconnect through, so this never mistakes a blip for a
/// departure.
fn is_graceful_leave(err: &ConnectionError) -> bool {
    matches!(err, ConnectionError::ApplicationClosed(frame) if frame.error_code == VarInt::from_u32(GOODBYE_CODE))
}

/// Pure S8 membership decision: iroh already authenticated `remote` as the
/// connection's endpoint id, so audio admission is exactly live roster membership.
pub(crate) fn audio_sender_admitted(remote: EndpointId, roster: &HashSet<EndpointId>) -> bool {
    roster.contains(&remote)
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub(crate) enum AudioAdmissionEvent {
    /// A signed gossip Announce/Update says the peer is in the live room roster.
    RosterPresent,
    /// Gossip reported a transient drop; keep admission during reconnect grace.
    TransientDropGrace,
    /// Graceful leave, transport Left eviction, or reconnect-grace expiry.
    Remove,
}

pub(crate) fn apply_audio_admission_event(
    roster: &mut HashSet<EndpointId>,
    peer_id: EndpointId,
    event: AudioAdmissionEvent,
) {
    match event {
        AudioAdmissionEvent::RosterPresent => {
            roster.insert(peer_id);
        }
        AudioAdmissionEvent::TransientDropGrace => {
            // Grace is not an authority to add membership; it only preserves an
            // already-admitted peer until either rejoin or grace expiry.
        }
        AudioAdmissionEvent::Remove => {
            roster.remove(&peer_id);
        }
    }
}

/// Owns a single peer's connection lifecycle for as long as the peer is in the
/// room: obtain a link, run the send/read loops, and on loss obtain a new one —
/// with capped backoff on the dialing side. The deterministic-initiator rule
/// (lower id dials, higher id accepts) is the same on first connect and every
/// reconnect, so exactly one shared connection forms each time.
async fn supervise(
    shared: Arc<Shared>,
    peer_id: EndpointId,
    mut inbound_rx: mpsc::Receiver<Connection>,
) {
    let is_dialer = shared.self_id.to_string() < peer_id.to_string();
    let mut backoff = INITIAL_BACKOFF;

    // Show "connecting" until the first link is actually up.
    let _ = shared
        .conn_events_tx
        .try_send(ConnEvent::Connecting(peer_id));

    let mut conn =
        match obtain_conn(&shared, peer_id, is_dialer, &mut inbound_rx, &mut backoff).await {
            Some(conn) => conn,
            None => return, // retired before we ever connected
        };

    loop {
        // A healthy link resets the dialer's backoff for the next outage.
        backoff = INITIAL_BACKOFF;

        let (send_tx, mut send_rx) = mpsc::channel::<Bytes>(SEND_QUEUE_DEPTH);
        shared.senders.lock().unwrap().insert(peer_id, send_tx);
        // Publish the live connection so an intentional leave can close it with
        // the goodbye code.
        shared
            .live_conns
            .lock()
            .unwrap()
            .insert(peer_id, conn.clone());
        let _ = shared
            .conn_events_tx
            .try_send(ConnEvent::Connected(peer_id));
        crate::log_msg(&format!("Transport: peer {:?} link up", peer_id));

        // Run until the link dies, a replacement arrives, or we're retired. The
        // send/read loops are held in abort-on-drop guards scoped to this block,
        // so however we leave it — normal exit or the supervisor being aborted
        // mid-`select` — both loops stop and release their `Connection` clones.
        let wake = {
            let conn_send = conn.clone();
            let _send_guard = AbortOnDrop(tokio::spawn(async move {
                while let Some(data) = send_rx.recv().await {
                    if conn_send.send_datagram(data).is_err() {
                        break;
                    }
                }
            }));

            let conn_read = conn.clone();
            let incoming_tx = shared.incoming_tx.clone();
            let _read_guard = AbortOnDrop(tokio::spawn(async move {
                while let Ok(bytes) = conn_read.read_datagram().await {
                    if incoming_tx.send((peer_id, bytes)).await.is_err() {
                        break;
                    }
                }
            }));

            // Only the acceptor watches for replacements: if the dialer notices
            // the drop and re-dials before our own `closed()` fires, we switch to
            // the new link immediately instead of waiting out the idle timeout.
            tokio::select! {
                reason = conn.closed() => Wake::Closed(reason),
                inbound = inbound_rx.recv(), if !is_dialer => match inbound {
                    Some(new_conn) => Wake::Replacement(new_conn),
                    None => Wake::Shutdown,
                },
            }
        };

        // Dropping the send handle makes `broadcast` skip this peer until the
        // link is back, instead of piling frames into a dead connection. The
        // live connection is gone too until a new one is established.
        shared.senders.lock().unwrap().remove(&peer_id);
        shared.live_conns.lock().unwrap().remove(&peer_id);

        match wake {
            Wake::Shutdown => return,
            Wake::Replacement(new_conn) => {
                crate::log_msg(&format!(
                    "Transport: peer {:?} replaced with new inbound link",
                    peer_id
                ));
                let _ = shared
                    .conn_events_tx
                    .try_send(ConnEvent::Connecting(peer_id));
                conn = new_conn;
            }
            Wake::Closed(reason) => {
                // A graceful application close means the peer left on purpose —
                // don't reconnect; tell the core to evict it now.
                if is_graceful_leave(&reason) {
                    crate::log_msg(&format!(
                        "Transport: peer {:?} left gracefully ({:?})",
                        peer_id, reason
                    ));
                    let _ = shared.conn_events_tx.try_send(ConnEvent::Left(peer_id));
                    return;
                }
                crate::log_msg(&format!(
                    "Transport: peer {:?} link dropped; reconnecting",
                    peer_id
                ));
                let _ = shared
                    .conn_events_tx
                    .try_send(ConnEvent::Connecting(peer_id));
                conn = match obtain_conn(&shared, peer_id, is_dialer, &mut inbound_rx, &mut backoff)
                    .await
                {
                    Some(conn) => conn,
                    None => return, // retired while reconnecting
                };
            }
        }
    }
}

/// Block until we hold a live connection to the peer, or `None` if the peer was
/// retired first. The dialer redials with capped exponential backoff; the
/// acceptor waits for the dialer to come to it (a closed `inbound_rx` means the
/// supervisor was retired).
async fn obtain_conn(
    shared: &Arc<Shared>,
    peer_id: EndpointId,
    is_dialer: bool,
    inbound_rx: &mut mpsc::Receiver<Connection>,
    backoff: &mut Duration,
) -> Option<Connection> {
    if is_dialer {
        loop {
            // Dial the retained full address (relay + direct addrs) so reconnects
            // don't depend on the address lookup; it's re-read each attempt so a
            // refreshed address (peer back on a new one) is picked up next retry.
            // Fall back to the bare id (lookup/relay resolution) only if we somehow
            // never recorded an address — the dialer path always carries one.
            let target = shared.addrs.lock().unwrap().get(&peer_id).cloned();
            let result = match target {
                Some(addr) => shared.endpoint.connect(addr, AUDIO_ALPN).await,
                None => shared.endpoint.connect(peer_id, AUDIO_ALPN).await,
            };
            match result {
                Ok(conn) => return Some(conn),
                Err(e) => {
                    crate::log_msg(&format!(
                        "Transport: dial to {:?} failed: {:?}; retrying in {:?}",
                        peer_id, e, backoff
                    ));
                    tokio::time::sleep(*backoff).await;
                    *backoff = (*backoff * 2).min(MAX_BACKOFF);
                }
            }
        }
    } else {
        inbound_rx.recv().await
    }
}

/// The persistent audio protocol handler. Registered ONCE on the app's single
/// long-lived [`Router`](iroh::protocol::Router), it delegates each inbound audio
/// connection to whatever session's [`Shared`] is currently bound, or drops it
/// when idle (no active call). This is what lets the endpoint + router outlive any
/// individual room session — the W7 friends listener needs the endpoint reachable
/// *between* calls — while the per-peer connection state stays per-session.
#[derive(Clone, Default)]
pub struct AudioRouter {
    /// The active session's transport state, swapped in on join and cleared on
    /// leave. `None` means "no call" → inbound audio links are dropped.
    current: Arc<StdMutex<Option<Arc<Shared>>>>,
}

impl std::fmt::Debug for AudioRouter {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("AudioRouter").finish_non_exhaustive()
    }
}

impl AudioRouter {
    pub fn new() -> Self {
        Self::default()
    }

    /// Route inbound audio connections to `transport`'s session (called on join).
    pub fn bind(&self, transport: &IrohTransport) {
        *self.current.lock().unwrap() = Some(transport.shared.clone());
    }

    /// Stop routing — drop inbound audio links until the next [`bind`](Self::bind)
    /// (called on leave). The endpoint/router stay alive; we just have nowhere to
    /// hand a fresh audio connection.
    pub fn clear(&self) {
        *self.current.lock().unwrap() = None;
    }
}

impl iroh::protocol::ProtocolHandler for AudioRouter {
    fn accept(
        &self,
        connection: Connection,
    ) -> impl std::future::Future<Output = Result<(), iroh::protocol::AcceptError>> + Send {
        let peer_id = connection.remote_id();
        // Snapshot the current session (clone the Arc) and release the lock before
        // any await — the guard isn't held across suspension points.
        let shared = self.current.lock().unwrap().clone();
        async move {
            // No active call → nothing to route this inbound link to; drop it.
            let Some(shared) = shared else {
                return Ok(());
            };
            // Deterministic roles: the lower id dials, the higher id accepts.
            // If we're the dialer for this peer we never consume inbound links
            // (we make our own), so just let this one drop.
            if shared.self_id.to_string() < peer_id.to_string() {
                return Ok(());
            }
            if !shared.audio_sender_admitted(peer_id) {
                crate::log_msg(&format!(
                    "Transport: rejected inbound audio from non-member {}",
                    crate::short_id(&peer_id.to_string())
                ));
                return Ok(());
            }
            // Route the connection to this peer's supervisor (creating it if the
            // inbound link arrives after the signed gossip Announce admitted it).
            // try_send keeps the protocol handler from ever blocking; a full queue
            // only happens if links are churning, and the supervisor gets the next one.
            let inbound_tx = shared.ensure_supervisor(peer_id).await;
            if inbound_tx.try_send(connection).is_err() {
                crate::log_msg(&format!(
                    "Transport: dropped inbound link from {:?} (queue full)",
                    peer_id
                ));
            }
            Ok(())
        }
    }
}

/// Protocol handler for the file-transfer plane (`FILES_ALPN`). Mirrors
/// [`AudioRouter`]: it's persistent on the router and bound to the active
/// session's [`Shared`] on join. On an inbound stream it authenticates the peer
/// (iroh ALPN handshake gives us `remote_id`), gates on **live room membership**
/// (same invariant as audio admission, so a former member can't pull files),
/// reads a single 32-byte attachment id, and streams back the matching blob from
/// the session serve store — or nothing if the id is unknown.
#[derive(Clone, Default)]
pub struct FileRouter {
    current: Arc<StdMutex<Option<Arc<Shared>>>>,
}

impl std::fmt::Debug for FileRouter {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("FileRouter").finish_non_exhaustive()
    }
}

impl FileRouter {
    pub fn new() -> Self {
        Self::default()
    }

    /// Route inbound file fetches to `transport`'s session (called on join).
    pub fn bind(&self, transport: &IrohTransport) {
        *self.current.lock().unwrap() = Some(transport.shared.clone());
    }

    /// Stop serving files until the next [`bind`](Self::bind) (called on leave).
    pub fn clear(&self) {
        *self.current.lock().unwrap() = None;
    }
}

/// Max bytes we'll read for a fetch *request* frame. A request is exactly one
/// 32-byte id; this small ceiling rejects a peer trying to stream us a huge
/// "request" as a cheap DoS.
const FILE_REQUEST_MAX: usize = 64;

impl iroh::protocol::ProtocolHandler for FileRouter {
    fn accept(
        &self,
        connection: Connection,
    ) -> impl std::future::Future<Output = Result<(), iroh::protocol::AcceptError>> + Send {
        let peer_id = connection.remote_id();
        let shared = self.current.lock().unwrap().clone();
        async move {
            // No active call → nothing to serve.
            let Some(shared) = shared else {
                return Ok(());
            };
            // Member gating: only current room members may fetch our files. Reuses
            // the audio admission roster (the authoritative room membership set).
            if !shared.audio_sender_admitted(peer_id) {
                crate::log_msg(&format!(
                    "Transport: rejected file fetch from non-member {}",
                    crate::short_id(&peer_id.to_string())
                ));
                return Ok(());
            }
            // Accept one bidirectional stream: read the id, write the bytes.
            let Ok((mut send, mut recv)) = connection.accept_bi().await else {
                return Ok(());
            };
            let Ok(req) = recv.read_to_end(FILE_REQUEST_MAX).await else {
                return Ok(());
            };
            let Some(id) = crate::files::parse_request(&req) else {
                return Ok(());
            };
            let blob = shared.served_files.lock().unwrap().get(&id);
            if let Some(blob) = blob {
                let _ = send.write_all(&blob).await;
            }
            // Finish either way: an unknown id closes with an empty body, which
            // the fetcher reads as a zero-length result and treats as "gone".
            let _ = send.finish();
            // CRITICAL: `finish()` only marks the stream's EOF — it does NOT wait
            // for the written bytes to be delivered and acknowledged. If we return
            // here the `connection` drops, and its CONNECTION_CLOSE can race ahead
            // of the still-in-flight stream data, so the fetcher's read aborts with
            // "connection lost". Wait for the fetcher to receive everything and
            // close the connection itself (it drops `conn` right after read_to_end);
            // that close is our signal the transfer landed. Bounded so a fetcher
            // that vanishes can't pin this task forever.
            let _ = tokio::time::timeout(FILE_FETCH_TIMEOUT, connection.closed()).await;
            Ok(())
        }
    }
}

pub struct IrohTransport {
    shared: Arc<Shared>,
    incoming_rx: tokio::sync::Mutex<Option<mpsc::Receiver<(EndpointId, Bytes)>>>,
    conn_events_rx: tokio::sync::Mutex<Option<mpsc::Receiver<ConnEvent>>>,
}

impl IrohTransport {
    /// Build a per-session transport over the app's persistent `endpoint`. The
    /// inbound audio handler is the persistent [`AudioRouter`] (registered once on
    /// the router) — call [`AudioRouter::bind`] with this transport to route this
    /// session's inbound links to it.
    pub fn new(endpoint: Endpoint) -> Self {
        let (incoming_tx, incoming_rx) = mpsc::channel(1000);
        let (conn_events_tx, conn_events_rx) = mpsc::channel(100);
        let self_id = endpoint.id();

        let shared = Arc::new(Shared {
            endpoint,
            self_id,
            senders: StdMutex::new(HashMap::new()),
            addrs: StdMutex::new(HashMap::new()),
            peers: tokio::sync::Mutex::new(HashMap::new()),
            live_conns: StdMutex::new(HashMap::new()),
            admitted_audio: StdMutex::new(HashSet::new()),
            served_files: StdMutex::new(crate::files::ServeStore::default()),
            incoming_tx,
            conn_events_tx,
        });

        Self {
            shared,
            incoming_rx: tokio::sync::Mutex::new(Some(incoming_rx)),
            conn_events_rx: tokio::sync::Mutex::new(Some(conn_events_rx)),
        }
    }

    /// Tear down for an intentional leave/quit: close every live connection with
    /// the graceful goodbye code so each remote peer evicts us promptly (its
    /// supervisor sees an application close, not a reconnectable drop), then stop
    /// all supervisors so none linger redialing the about-to-close endpoint.
    /// Call this before shutting the router down.
    pub async fn leave(&self) {
        let conns: Vec<Connection> = self
            .shared
            .live_conns
            .lock()
            .unwrap()
            .drain()
            .map(|(_, c)| c)
            .collect();
        for conn in &conns {
            conn.close(VarInt::from_u32(GOODBYE_CODE), b"leave");
        }
        // Stop every supervisor so it can't re-dial during/after teardown.
        let mut peers = self.shared.peers.lock().await;
        for (_, handle) in peers.drain() {
            handle.supervisor.abort();
        }
        self.shared.senders.lock().unwrap().clear();
        self.shared.addrs.lock().unwrap().clear();
        self.shared.admitted_audio.lock().unwrap().clear();
        self.shared.served_files.lock().unwrap().clear();
        // Give the CONNECTION_CLOSE frames a moment to flush before the caller
        // shuts the endpoint/router down (the `conns` clones are still alive
        // here, so the endpoint can still transmit them).
        tokio::time::sleep(Duration::from_millis(150)).await;
    }

    /// Admit a peer to this session's audio plane. Core calls this from verified
    /// gossip roster events; the transport never derives membership on its own.
    pub fn admit_audio_sender(&self, peer_id: EndpointId) {
        self.shared
            .apply_audio_admission(peer_id, AudioAdmissionEvent::RosterPresent);
    }

    /// Preserve an already-admitted peer through the reconnect grace window.
    pub fn keep_audio_sender_for_reconnect_grace(&self, peer_id: EndpointId) {
        self.shared
            .apply_audio_admission(peer_id, AudioAdmissionEvent::TransientDropGrace);
    }

    /// Remove a peer from audio admission before tearing down transport/jitter state.
    pub fn remove_audio_sender(&self, peer_id: EndpointId) {
        self.shared
            .apply_audio_admission(peer_id, AudioAdmissionEvent::Remove);
    }

    pub fn audio_sender_admitted(&self, peer_id: EndpointId) -> bool {
        self.shared.audio_sender_admitted(peer_id)
    }

    /// Make `bytes` available to room members under `id` for the rest of this
    /// session (served by the [`FileRouter`] handler). Called by core when we
    /// send a chat file. The blob is cleared on leave.
    pub fn serve_attachment(&self, id: AttachmentId, bytes: Arc<Vec<u8>>) {
        if !self.shared.served_files.lock().unwrap().insert(id, bytes) {
            crate::log_msg("Transport: refused to serve an over-budget blob");
        }
    }

    /// Drop a previously-served blob (e.g. a music track no longer current-or-next).
    pub fn forget_attachment(&self, id: AttachmentId) {
        self.shared.served_files.lock().unwrap().remove(&id);
    }

    /// Fetch `size` bytes stored under `id` from peer `from` over the files plane.
    /// Shared core of `fetch_attachment` and music-track fetching: dials
    /// `FILES_ALPN`, writes the 32-byte id, and reads bounded by `size`.
    pub async fn fetch_blob(
        &self,
        from: EndpointId,
        id: AttachmentId,
        size: u64,
    ) -> Result<Vec<u8>, NetError> {
        if !crate::files::size_within_cap(size) {
            return Err(NetError::Other("attachment size out of range".to_string()));
        }
        let addr = self.shared.addrs.lock().unwrap().get(&from).cloned();
        let connect = async {
            match addr {
                Some(addr) => self.shared.endpoint.connect(addr, FILES_ALPN).await,
                None => self.shared.endpoint.connect(from, FILES_ALPN).await,
            }
        };
        let conn = tokio::time::timeout(FILE_FETCH_TIMEOUT, connect)
            .await
            .map_err(|_| NetError::Other("file fetch: connect timed out".to_string()))?
            .map_err(|e| NetError::Other(format!("file fetch: connect failed: {e}")))?;

        let (mut send, mut recv) = conn
            .open_bi()
            .await
            .map_err(|e| NetError::Other(format!("file fetch: open stream failed: {e}")))?;
        send.write_all(&id)
            .await
            .map_err(|e| NetError::Other(format!("file fetch: request write failed: {e}")))?;
        send.finish()
            .map_err(|e| NetError::Other(format!("file fetch: request finish failed: {e}")))?;

        // `read_to_end(size)` errors if the stream exceeds `size`, rejecting an
        // overlong transfer; the exact-length check below rejects a short one.
        let read = recv.read_to_end(size as usize);
        let bytes = tokio::time::timeout(FILE_FETCH_TIMEOUT, read)
            .await
            .map_err(|_| NetError::Other("file fetch: read timed out".to_string()))?
            .map_err(|e| NetError::Other(format!("file fetch: read failed: {e}")))?;
        if bytes.is_empty() {
            return Err(NetError::Other(
                "file fetch: sender no longer has the file".to_string(),
            ));
        }
        // Exact transfer required (Phase 3C): a truncated body must not be
        // cached/saved/decoded as if it were the declared attachment.
        if bytes.len() as u64 != size {
            return Err(NetError::Other(format!(
                "file fetch: incomplete transfer ({} of {size} bytes)",
                bytes.len()
            )));
        }
        Ok(bytes)
    }

    /// Snapshot the selected QUIC path of every live audio connection, for the
    /// UI's per-peer connection badge (direct/relay, RTT, loss, bitrate).
    /// Cheap and lock-light: the `live_conns` guard is released before touching
    /// any connection, and `Connection::paths()` reads shared state without I/O.
    pub fn connection_stats(&self) -> Vec<(EndpointId, crate::network::PathSnapshot)> {
        // Clone the connections out so the map lock isn't held while we inspect
        // paths (a supervisor inserts/removes entries as links come and go).
        let conns: Vec<(EndpointId, Connection)> = self
            .shared
            .live_conns
            .lock()
            .unwrap()
            .iter()
            .map(|(id, conn)| (*id, conn.clone()))
            .collect();
        conns
            .into_iter()
            .filter_map(|(id, conn)| {
                let paths = conn.paths();
                // The selected path is the one carrying application data. In the
                // brief window where none is flagged (e.g. mid-migration), fall
                // back to the first open path rather than dropping the badge.
                let path = paths
                    .iter()
                    .find(|p| p.is_selected())
                    .or_else(|| paths.iter().next())?;
                let stats = path.stats();
                // Per-variant display: `TransportAddr`'s own `Display` prefixes
                // a scheme ("ip:1.2.3.4:5") that's noise next to the badge's
                // Direct/Relay label.
                let remote_addr = match path.remote_addr() {
                    iroh::TransportAddr::Ip(sock) => sock.to_string(),
                    iroh::TransportAddr::Relay(url) => url.to_string(),
                    other => other.to_string(),
                };
                Some((
                    id,
                    crate::network::PathSnapshot {
                        is_relay: path.remote_addr().is_relay(),
                        remote_addr,
                        rtt: stats.rtt,
                        tx_bytes: stats.udp_tx.bytes,
                        rx_bytes: stats.udp_rx.bytes,
                        tx_datagrams: stats.udp_tx.datagrams,
                        lost_packets: stats.lost_packets,
                    },
                ))
            })
            .collect()
    }

    /// Fetch a chat attachment's bytes from its sender over the file plane.
    pub async fn fetch_attachment(
        &self,
        from: EndpointId,
        att: &ChatAttachment,
    ) -> Result<Vec<u8>, NetError> {
        self.fetch_blob(from, att.id, att.size).await
    }
}

#[async_trait]
impl NetworkTransport for IrohTransport {
    async fn connect_peer(&self, addr: iroh::EndpointAddr) {
        let peer_id = addr.id;
        // Retain (or refresh) the peer's full address so the dialer can re-reach
        // it across reconnects without leaning on the address lookup.
        self.shared.addrs.lock().unwrap().insert(peer_id, addr);
        // Start (or confirm) the peer's supervisor. It owns dialing/accepting and
        // reconnection from here on; this call is just the reactive trigger.
        self.shared.ensure_supervisor(peer_id).await;
    }

    async fn disconnect_peer(&self, peer_id: EndpointId) {
        self.shared.remove(peer_id).await;
    }

    fn broadcast(&self, data: Bytes) {
        let senders = self.shared.senders.lock().unwrap();
        for tx in senders.values() {
            // Drop on a full queue: stale audio is worthless, and we must never
            // block the encode thread on a slow peer.
            let _ = tx.try_send(data.clone());
        }
    }

    async fn receive_datagrams(&self) -> Result<Receiver<(EndpointId, Bytes)>, NetError> {
        let mut rx_guard = self.incoming_rx.lock().await;
        rx_guard
            .take()
            .ok_or_else(|| NetError::Other("Datagram receiver already subscribed".to_string()))
    }

    async fn subscribe_conn_events(&self) -> Result<Receiver<ConnEvent>, NetError> {
        let mut rx_guard = self.conn_events_rx.lock().await;
        rx_guard
            .take()
            .ok_or_else(|| NetError::Other("Connection events already subscribed".to_string()))
    }
}

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

    fn endpoint_id() -> EndpointId {
        SecretKey::generate().public()
    }

    #[test]
    fn audio_sender_admission_accepts_roster_member() {
        let member = endpoint_id();
        let roster = HashSet::from([member]);

        assert!(audio_sender_admitted(member, &roster));
    }

    #[test]
    fn audio_sender_admission_rejects_unknown_sender() {
        let member = endpoint_id();
        let stranger = endpoint_id();
        let roster = HashSet::from([member]);

        assert!(!audio_sender_admitted(stranger, &roster));
    }

    #[test]
    fn audio_sender_admission_rejects_former_member_after_roster_removal() {
        let former = endpoint_id();
        let mut roster = HashSet::from([former]);
        assert!(audio_sender_admitted(former, &roster));

        roster.remove(&former);

        assert!(!audio_sender_admitted(former, &roster));
    }

    #[test]
    fn audio_sender_admission_waits_for_mid_join_announce() {
        let joining_peer = endpoint_id();
        let mut roster = HashSet::new();

        assert!(!audio_sender_admitted(joining_peer, &roster));

        roster.insert(joining_peer);

        assert!(audio_sender_admitted(joining_peer, &roster));
    }

    #[test]
    fn audio_admission_lifecycle_keeps_peer_through_transient_grace() {
        let peer = endpoint_id();
        let mut roster = HashSet::new();

        apply_audio_admission_event(&mut roster, peer, AudioAdmissionEvent::RosterPresent);
        assert!(audio_sender_admitted(peer, &roster));

        apply_audio_admission_event(&mut roster, peer, AudioAdmissionEvent::TransientDropGrace);
        assert!(audio_sender_admitted(peer, &roster));
    }

    #[test]
    fn audio_admission_lifecycle_does_not_add_unknown_peer_on_grace_event() {
        let peer = endpoint_id();
        let mut roster = HashSet::new();

        apply_audio_admission_event(&mut roster, peer, AudioAdmissionEvent::TransientDropGrace);

        assert!(!audio_sender_admitted(peer, &roster));
    }

    #[test]
    fn audio_admission_lifecycle_removes_peer_on_leave_or_grace_expiry() {
        let peer = endpoint_id();
        let mut roster = HashSet::from([peer]);

        apply_audio_admission_event(&mut roster, peer, AudioAdmissionEvent::Remove);

        assert!(!audio_sender_admitted(peer, &roster));
    }
}