#[cfg(coverage)]
fn upstream_stale_drop_budget() -> Duration {
    let drop_ms = std::env::var("LESAVKA_UPSTREAM_STALE_DROP_MS")
        .ok()
        .and_then(|value| value.trim().parse::<u64>().ok())
        .unwrap_or(80);
    Duration::from_millis(drop_ms)
}

#[cfg(coverage)]
fn retain_freshest_video_packet(
    pending: &mut std::collections::VecDeque<VideoPacket>,
) -> usize {
    if pending.len() <= 1 {
        return 0;
    }
    let newest = pending.pop_back().expect("non-empty pending video queue");
    let dropped = pending.len();
    pending.clear();
    pending.push_back(newest);
    dropped
}

#[cfg(coverage)]
fn retain_freshest_audio_packet(
    pending: &mut std::collections::VecDeque<AudioPacket>,
) -> usize {
    if pending.len() <= 1 {
        return 0;
    }
    let newest = pending.pop_back().expect("non-empty pending audio queue");
    let dropped = pending.len();
    pending.clear();
    pending.push_back(newest);
    dropped
}

#[cfg(coverage)]
#[tonic::async_trait]
impl Relay for Handler {
    type StreamKeyboardStream = ReceiverStream<Result<KeyboardReport, Status>>;
    type StreamMouseStream = ReceiverStream<Result<MouseReport, Status>>;
    type CaptureVideoStream = VideoStream;
    type CaptureAudioStream = AudioStream;
    type StreamMicrophoneStream = ReceiverStream<Result<Empty, Status>>;
    type StreamCameraStream = ReceiverStream<Result<Empty, Status>>;

    async fn stream_keyboard(
        &self,
        req: Request<tonic::Streaming<KeyboardReport>>,
    ) -> Result<Response<Self::StreamKeyboardStream>, Status> {
        let (tx, rx) = tokio::sync::mpsc::channel(32);
        let kb = self.kb.clone();
        let report_delay = live_keyboard_report_delay();

        tokio::spawn(async move {
            let mut s = req.into_inner();
            while let Some(pkt) = s.next().await.transpose()? {
                let _ = runtime_support::write_hid_report(&kb, &hid_endpoint(0), &pkt.data).await;
                tx.send(Ok(pkt)).await.ok();
                if !report_delay.is_zero() {
                    #[cfg(not(coverage))]
                    tokio::time::sleep(report_delay).await;
                }
            }
            Ok::<(), Status>(())
        });

        Ok(Response::new(ReceiverStream::new(rx)))
    }

    async fn stream_mouse(
        &self,
        req: Request<tonic::Streaming<MouseReport>>,
    ) -> Result<Response<Self::StreamMouseStream>, Status> {
        let (tx, rx) = tokio::sync::mpsc::channel(32);
        let ms = self.ms.clone();

        tokio::spawn(async move {
            let mut s = req.into_inner();
            while let Some(pkt) = s.next().await.transpose()? {
                let _ = runtime_support::write_hid_report(&ms, &hid_endpoint(1), &pkt.data).await;
                tx.send(Ok(pkt)).await.ok();
            }
            Ok::<(), Status>(())
        });

        Ok(Response::new(ReceiverStream::new(rx)))
    }

    async fn stream_microphone(
        &self,
        req: Request<tonic::Streaming<AudioPacket>>,
    ) -> Result<Response<Self::StreamMicrophoneStream>, Status> {
        let lease = self.upstream_media_rt.activate_microphone();
        let Some(microphone_sink_permit) = self
            .upstream_media_rt
            .reserve_microphone_sink(lease.generation)
            .await
        else {
            return Err(Status::aborted(
                "microphone stream superseded before sink became available",
            ));
        };
        let uac_dev = std::env::var("LESAVKA_UAC_DEV").unwrap_or_else(|_| "hw:UAC2Gadget,0".into());
        let mut sink = runtime_support::open_voice_with_retry(&uac_dev)
            .await
            .map_err(|e| {
                self.upstream_media_rt.close_microphone(lease.generation);
                Status::internal(format!("{e:#}"))
            })?;
        let (tx, rx) = tokio::sync::mpsc::channel(1);
        let upstream_media_rt = self.upstream_media_rt.clone();

        tokio::spawn(async move {
            let _microphone_sink_permit = microphone_sink_permit;
            let mut inbound = req.into_inner();
            let mut pending = std::collections::VecDeque::new();
            let mut inbound_closed = false;
            let stale_drop_budget = upstream_stale_drop_budget();
            loop {
                if !upstream_media_rt.is_microphone_active(lease.generation) {
                    break;
                }
                if !inbound_closed {
                    let next_packet = tokio::select! {
                        packet = inbound.next() => Some(packet),
                        _ = tokio::time::sleep(Duration::from_millis(25)) => None,
                    };
                    if let Some(next_packet) = next_packet {
                        match next_packet.transpose()? {
                            Some(pkt) => {
                                pending.push_back(pkt);
                                let _ = retain_freshest_audio_packet(&mut pending);
                            }
                            None => inbound_closed = true,
                        }
                    }
                }
                let Some(mut pkt) = pending.pop_front() else {
                    if inbound_closed {
                        break;
                    }
                    continue;
                };
                let plan = match upstream_media_rt.plan_audio_pts(pkt.pts) {
                    lesavka_server::upstream_media_runtime::UpstreamPlanDecision::AwaitingPair => {
                        if inbound_closed {
                            continue;
                        }
                        pending.push_front(pkt);
                        continue;
                    }
                    lesavka_server::upstream_media_runtime::UpstreamPlanDecision::DropBeforeOverlap => {
                        continue;
                    }
                    lesavka_server::upstream_media_runtime::UpstreamPlanDecision::Play(plan) => plan,
                };
                if plan.late_by > stale_drop_budget {
                    continue;
                }
                tokio::time::sleep_until(plan.due_at).await;
                let actual_late_by = tokio::time::Instant::now()
                    .checked_duration_since(plan.due_at)
                    .unwrap_or_default();
                if actual_late_by > stale_drop_budget {
                    continue;
                }
                pkt.pts = plan.local_pts_us;
                sink.push(&pkt);
            }
            sink.finish();
            upstream_media_rt.close_microphone(lease.generation);
            let _ = tx.send(Ok(Empty {})).await;
            Ok::<(), Status>(())
        });

        Ok(Response::new(ReceiverStream::new(rx)))
    }

    async fn stream_camera(
        &self,
        req: Request<tonic::Streaming<VideoPacket>>,
    ) -> Result<Response<Self::StreamCameraStream>, Status> {
        let cfg = camera::current_camera_config();
        let upstream_lease = self.upstream_media_rt.activate_camera();
        let (session_id, relay, _relay_reused) = self.camera_rt.activate(&cfg).await?;
        let camera_rt = self.camera_rt.clone();
        let upstream_media_rt = self.upstream_media_rt.clone();
        let (tx, rx) = tokio::sync::mpsc::channel(1);
        let frame_step_us = (1_000_000u64 / u64::from(cfg.fps.max(1))).max(1);

        tokio::spawn(async move {
            let mut s = req.into_inner();
            let mut pending = std::collections::VecDeque::new();
            let mut inbound_closed = false;
            let stale_drop_budget = upstream_stale_drop_budget();
            loop {
                if !camera_rt.is_active(session_id)
                    || !upstream_media_rt.is_camera_active(upstream_lease.generation)
                {
                    break;
                }
                if !inbound_closed {
                    let next_packet = tokio::select! {
                        packet = s.next() => Some(packet),
                        _ = tokio::time::sleep(Duration::from_millis(25)) => None,
                    };
                    if let Some(next_packet) = next_packet {
                        match next_packet.transpose()? {
                            Some(pkt) => {
                                pending.push_back(pkt);
                                let _ = retain_freshest_video_packet(&mut pending);
                            }
                            None => inbound_closed = true,
                        }
                    }
                }
                let Some(mut pkt) = pending.pop_front() else {
                    if inbound_closed {
                        break;
                    }
                    continue;
                };
                let plan = match upstream_media_rt.plan_video_pts(pkt.pts, frame_step_us) {
                    lesavka_server::upstream_media_runtime::UpstreamPlanDecision::AwaitingPair => {
                        if inbound_closed {
                            continue;
                        }
                        pending.push_front(pkt);
                        continue;
                    }
                    lesavka_server::upstream_media_runtime::UpstreamPlanDecision::DropBeforeOverlap => {
                        continue;
                    }
                    lesavka_server::upstream_media_runtime::UpstreamPlanDecision::Play(plan) => plan,
                };
                if !upstream_media_rt
                    .wait_for_audio_master(plan.local_pts_us, plan.due_at)
                    .await
                {
                    continue;
                }
                if plan.late_by > stale_drop_budget {
                    let _ = retain_freshest_video_packet(&mut pending);
                    continue;
                }
                tokio::time::sleep_until(plan.due_at).await;
                let actual_late_by = tokio::time::Instant::now()
                    .checked_duration_since(plan.due_at)
                    .unwrap_or_default();
                if actual_late_by > stale_drop_budget {
                    let _ = retain_freshest_video_packet(&mut pending);
                    continue;
                }
                pkt.pts = plan.local_pts_us;
                relay.feed(pkt);
            }
            upstream_media_rt.close_camera(upstream_lease.generation);
            tx.send(Ok(Empty {})).await.ok();
            Ok::<(), Status>(())
        });

        Ok(Response::new(ReceiverStream::new(rx)))
    }

    async fn capture_video(
        &self,
        req: Request<MonitorRequest>,
    ) -> Result<Response<Self::CaptureVideoStream>, Status> {
        self.capture_video_reply(req.into_inner()).await
    }

    async fn capture_audio(
        &self,
        _req: Request<MonitorRequest>,
    ) -> Result<Response<Self::CaptureAudioStream>, Status> {
        Err(Status::internal(
            "audio capture unavailable in coverage harness",
        ))
    }

    async fn paste_text(&self, req: Request<PasteRequest>) -> Result<Response<PasteReply>, Status> {
        self.paste_text_reply(req).await
    }

    async fn reset_usb(&self, _req: Request<Empty>) -> Result<Response<ResetUsbReply>, Status> {
        self.reset_usb_reply().await
    }

    async fn recover_usb(
        &self,
        _req: Request<Empty>,
    ) -> Result<Response<ResetUsbReply>, Status> {
        self.recover_usb_reply().await
    }

    async fn recover_uac(
        &self,
        _req: Request<Empty>,
    ) -> Result<Response<ResetUsbReply>, Status> {
        self.recover_uac_reply().await
    }

    async fn recover_uvc(
        &self,
        _req: Request<Empty>,
    ) -> Result<Response<ResetUsbReply>, Status> {
        self.recover_uvc_reply().await
    }

    async fn get_capture_power(
        &self,
        _req: Request<Empty>,
    ) -> Result<Response<CapturePowerState>, Status> {
        self.get_capture_power_reply().await
    }

    async fn set_capture_power(
        &self,
        req: Request<SetCapturePowerRequest>,
    ) -> Result<Response<CapturePowerState>, Status> {
        self.set_capture_power_reply(req).await
    }

    async fn get_calibration(
        &self,
        _req: Request<Empty>,
    ) -> Result<Response<CalibrationState>, Status> {
        self.get_calibration_reply().await
    }

    async fn calibrate(
        &self,
        req: Request<CalibrationRequest>,
    ) -> Result<Response<CalibrationState>, Status> {
        self.calibrate_reply(req).await
    }
}