//! Shared upstream media telemetry for the relay child and launcher.

use serde::{Deserialize, Serialize};
use std::{
    fs,
    path::{Path, PathBuf},
    sync::{Arc, Mutex},
    time::{Duration, Instant, SystemTime, UNIX_EPOCH},
};

/// Environment variable used to point the relay child at the upstream telemetry file.
pub const UPLINK_TELEMETRY_ENV: &str = "LESAVKA_UPLINK_TELEMETRY";

/// Default JSON file used by the relay child to publish upstream queue telemetry.
pub const DEFAULT_UPLINK_TELEMETRY_PATH: &str = "/tmp/lesavka-uplink-telemetry.json";

const FLUSH_INTERVAL: Duration = Duration::from_millis(250);

/// Camera/microphone telemetry sampled by the launcher diagnostics pane.
#[derive(Debug, Clone, Default, Serialize, Deserialize, PartialEq)]
pub struct UplinkTelemetrySnapshot {
    /// Last time the relay child wrote this snapshot, in Unix milliseconds.
    pub updated_at_unix_ms: u128,
    /// Upstream webcam queue telemetry.
    pub camera: UpstreamStreamTelemetry,
    /// Upstream microphone queue telemetry.
    pub microphone: UpstreamStreamTelemetry,
}

/// Per-stream state for measuring reconnect churn and queue staleness.
#[derive(Debug, Clone, Default, Serialize, Deserialize, PartialEq)]
pub struct UpstreamStreamTelemetry {
    /// Whether the stream is enabled for the current relay session.
    pub enabled: bool,
    /// Whether the stream is currently attached to an active gRPC uplink.
    pub connected: bool,
    /// Number of gRPC connection attempts during the current relay child lifetime.
    pub reconnect_count: u64,
    /// Current bounded queue depth inside the relay child.
    pub queue_depth: u32,
    /// Highest observed bounded queue depth inside the relay child.
    pub queue_peak: u32,
    /// Age of the most recently enqueued packet, measured at queue admission time.
    pub latest_enqueue_age_ms: f32,
    /// Highest observed packet age at queue admission time.
    pub enqueue_age_peak_ms: f32,
    /// Highest observed time spent blocked while enqueuing into the async uplink queue.
    pub enqueue_block_peak_ms: f32,
    /// Number of packets admitted into the async uplink queue.
    pub packets_enqueued: u64,
    /// Number of packets emitted from the async uplink queue into the gRPC stream.
    pub packets_streamed: u64,
    /// Number of packets intentionally dropped before queue admission.
    pub dropped_packets: u64,
    /// Number of packets dropped because the bounded queue was already full.
    pub dropped_queue_full_packets: u64,
    /// Number of packets dropped because they exceeded the live-call age budget.
    pub dropped_stale_packets: u64,
    /// Age of the most recently streamed packet after queue residence was accounted for.
    pub latest_delivery_age_ms: f32,
    /// Highest observed streamed packet age after queue residence was accounted for.
    pub delivery_age_peak_ms: f32,
    /// Most recent queue/setup failure for this stream, if any.
    pub last_error: String,
}

#[derive(Clone, Copy, Debug)]
pub enum UpstreamStreamKind {
    Camera,
    Microphone,
}

#[derive(Debug)]
struct TelemetryState {
    path: PathBuf,
    snapshot: UplinkTelemetrySnapshot,
    last_flush: Instant,
}

/// Shared publisher used by the relay child to update queue telemetry.
#[derive(Clone, Debug)]
pub struct UplinkTelemetryPublisher {
    inner: Arc<Mutex<TelemetryState>>,
}

/// Per-stream handle used by individual uplink loops.
#[derive(Clone, Debug)]
pub struct UplinkTelemetryHandle {
    kind: UpstreamStreamKind,
    inner: Arc<Mutex<TelemetryState>>,
}

impl UplinkTelemetryPublisher {
    /// Creates a publisher seeded with the current session's enabled uplinks.
    #[must_use]
    pub fn from_env(camera_enabled: bool, microphone_enabled: bool) -> Self {
        let path = std::env::var(UPLINK_TELEMETRY_ENV)
            .map(PathBuf::from)
            .unwrap_or_else(|_| PathBuf::from(DEFAULT_UPLINK_TELEMETRY_PATH));
        Self::new(path, camera_enabled, microphone_enabled)
    }

    /// Creates a publisher that writes to an explicit JSON path.
    #[must_use]
    pub fn new(path: PathBuf, camera_enabled: bool, microphone_enabled: bool) -> Self {
        let state = TelemetryState {
            path,
            snapshot: UplinkTelemetrySnapshot {
                updated_at_unix_ms: unix_time_ms(),
                camera: UpstreamStreamTelemetry {
                    enabled: camera_enabled,
                    ..UpstreamStreamTelemetry::default()
                },
                microphone: UpstreamStreamTelemetry {
                    enabled: microphone_enabled,
                    ..UpstreamStreamTelemetry::default()
                },
            },
            last_flush: Instant::now() - FLUSH_INTERVAL,
        };
        let publisher = Self {
            inner: Arc::new(Mutex::new(state)),
        };
        publisher.flush_now();
        publisher
    }

    /// Returns a per-stream handle for camera or microphone updates.
    #[must_use]
    pub fn handle(&self, kind: UpstreamStreamKind) -> UplinkTelemetryHandle {
        UplinkTelemetryHandle {
            kind,
            inner: Arc::clone(&self.inner),
        }
    }

    /// Forces an immediate write of the current snapshot.
    pub fn flush_now(&self) {
        if let Ok(mut state) = self.inner.lock() {
            write_snapshot(&mut state, true);
        }
    }
}

impl UplinkTelemetryHandle {
    /// Updates whether this feed is intentionally active in the current relay session.
    pub fn record_enabled(&self, enabled: bool) {
        self.update(true, |stream| {
            stream.enabled = enabled;
            if !enabled {
                stream.connected = false;
                stream.queue_depth = 0;
                stream.latest_enqueue_age_ms = 0.0;
                stream.latest_delivery_age_ms = 0.0;
                stream.last_error.clear();
            }
        });
    }

    /// Records a fresh gRPC connection attempt for this stream.
    pub fn record_reconnect_attempt(&self) {
        self.update(false, |stream| {
            stream.connected = false;
            stream.queue_depth = 0;
            stream.reconnect_count = stream.reconnect_count.saturating_add(1);
            stream.last_error.clear();
        });
    }

    /// Marks the stream as successfully connected to the relay server.
    pub fn record_connected(&self) {
        self.update(true, |stream| {
            stream.connected = true;
            stream.last_error.clear();
        });
    }

    /// Marks the stream as disconnected and stores the latest error detail.
    pub fn record_disconnect(&self, error: impl AsRef<str>) {
        let error = error.as_ref().trim().to_string();
        self.update(true, |stream| {
            stream.connected = false;
            stream.queue_depth = 0;
            stream.latest_enqueue_age_ms = 0.0;
            stream.latest_delivery_age_ms = 0.0;
            if !error.is_empty() {
                stream.last_error = error.clone();
            }
        });
    }

    /// Records one packet entering the async uplink queue.
    pub fn record_enqueue(&self, queue_depth: u32, enqueue_age_ms: f32, enqueue_block_ms: f32) {
        self.update(false, |stream| {
            stream.queue_depth = queue_depth;
            stream.queue_peak = stream.queue_peak.max(queue_depth);
            stream.latest_enqueue_age_ms = enqueue_age_ms.max(0.0);
            stream.enqueue_age_peak_ms = stream.enqueue_age_peak_ms.max(enqueue_age_ms.max(0.0));
            stream.enqueue_block_peak_ms =
                stream.enqueue_block_peak_ms.max(enqueue_block_ms.max(0.0));
            stream.packets_enqueued = stream.packets_enqueued.saturating_add(1);
            stream.last_error.clear();
        });
    }

    /// Records packets dropped because the bounded queue was already full.
    pub fn record_queue_full_drop(&self, count: u64) {
        self.update(false, |stream| {
            stream.dropped_packets = stream.dropped_packets.saturating_add(count);
            stream.dropped_queue_full_packets =
                stream.dropped_queue_full_packets.saturating_add(count);
        });
    }

    /// Records packets dropped because they exceeded the live-call age budget.
    pub fn record_stale_drop(&self, count: u64) {
        self.update(false, |stream| {
            stream.dropped_packets = stream.dropped_packets.saturating_add(count);
            stream.dropped_stale_packets = stream.dropped_stale_packets.saturating_add(count);
        });
    }

    /// Records one packet emitted from the bounded queue into the gRPC stream.
    pub fn record_streamed(&self, queue_depth: u32, delivery_age_ms: f32) {
        self.update(false, |stream| {
            stream.connected = true;
            stream.queue_depth = queue_depth;
            stream.latest_delivery_age_ms = delivery_age_ms.max(0.0);
            stream.delivery_age_peak_ms = stream.delivery_age_peak_ms.max(delivery_age_ms.max(0.0));
            stream.packets_streamed = stream.packets_streamed.saturating_add(1);
            stream.last_error.clear();
        });
    }

    fn update(&self, force_flush: bool, update_stream: impl FnOnce(&mut UpstreamStreamTelemetry)) {
        if let Ok(mut state) = self.inner.lock() {
            state.snapshot.updated_at_unix_ms = unix_time_ms();
            update_stream(stream_for_kind(&mut state.snapshot, self.kind));
            write_snapshot(&mut state, force_flush);
        }
    }
}

/// Loads the latest upstream telemetry snapshot written by the relay child.
pub fn load_uplink_telemetry(path: &Path) -> Option<UplinkTelemetrySnapshot> {
    let raw = fs::read_to_string(path).ok()?;
    serde_json::from_str(&raw).ok()
}

fn stream_for_kind(
    snapshot: &mut UplinkTelemetrySnapshot,
    kind: UpstreamStreamKind,
) -> &mut UpstreamStreamTelemetry {
    match kind {
        UpstreamStreamKind::Camera => &mut snapshot.camera,
        UpstreamStreamKind::Microphone => &mut snapshot.microphone,
    }
}

fn write_snapshot(state: &mut TelemetryState, force_flush: bool) {
    if !force_flush && state.last_flush.elapsed() < FLUSH_INTERVAL {
        return;
    }
    if let Ok(rendered) = serde_json::to_string(&state.snapshot) {
        let _ = fs::write(&state.path, rendered);
        state.last_flush = Instant::now();
    }
}

fn unix_time_ms() -> u128 {
    SystemTime::now()
        .duration_since(UNIX_EPOCH)
        .map(|duration| duration.as_millis())
        .unwrap_or_default()
}

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

    #[test]
    fn handle_updates_keep_queue_peaks_and_errors() {
        let temp_dir = tempfile::tempdir().expect("tempdir");
        let path = temp_dir.path().join("uplink.json");
        let publisher = UplinkTelemetryPublisher::new(path.clone(), true, false);
        let camera = publisher.handle(UpstreamStreamKind::Camera);

        camera.record_reconnect_attempt();
        camera.record_connected();
        camera.record_enqueue(3, 41.0, 6.0);
        camera.record_enqueue(1, 12.0, 2.0);
        camera.record_streamed(0, 55.0);
        camera.record_queue_full_drop(2);
        camera.record_stale_drop(3);
        camera.record_disconnect("stream ended");
        publisher.flush_now();

        let snapshot = load_uplink_telemetry(&path).expect("load snapshot");
        assert!(snapshot.camera.enabled);
        assert!(!snapshot.microphone.enabled);
        assert!(!snapshot.camera.connected);
        assert_eq!(snapshot.camera.reconnect_count, 1);
        assert_eq!(snapshot.camera.queue_peak, 3);
        assert_eq!(snapshot.camera.latest_enqueue_age_ms, 0.0);
        assert_eq!(snapshot.camera.enqueue_age_peak_ms, 41.0);
        assert_eq!(snapshot.camera.enqueue_block_peak_ms, 6.0);
        assert_eq!(snapshot.camera.packets_enqueued, 2);
        assert_eq!(snapshot.camera.packets_streamed, 1);
        assert_eq!(snapshot.camera.dropped_packets, 5);
        assert_eq!(snapshot.camera.dropped_queue_full_packets, 2);
        assert_eq!(snapshot.camera.dropped_stale_packets, 3);
        assert_eq!(snapshot.camera.delivery_age_peak_ms, 55.0);
        assert_eq!(snapshot.camera.last_error, "stream ended");
    }

    /// Soft-paused streams should report disabled without looking stale or crashed.
    #[test]
    fn handle_enabled_updates_expose_live_soft_pause_state() {
        let temp_dir = tempfile::tempdir().expect("tempdir");
        let path = temp_dir.path().join("uplink.json");
        let publisher = UplinkTelemetryPublisher::new(path.clone(), true, true);
        let microphone = publisher.handle(UpstreamStreamKind::Microphone);

        microphone.record_connected();
        microphone.record_enqueue(4, 12.0, 0.0);
        microphone.record_enabled(false);
        publisher.flush_now();

        let snapshot = load_uplink_telemetry(&path).expect("load snapshot");
        assert!(!snapshot.microphone.enabled);
        assert!(!snapshot.microphone.connected);
        assert_eq!(snapshot.microphone.queue_depth, 0);
        assert_eq!(snapshot.microphone.latest_enqueue_age_ms, 0.0);
        assert!(snapshot.microphone.last_error.is_empty());
    }
}