//! AZ-649 acceptance criteria.
//!
//! AC-1 — telemetry reaches all three downstream consumers at the
//! arriving rate.
//! AC-2 — slow consumer drops, fast consumers unaffected.
//! AC-3 — `latest_snapshot()` is monotonic across concurrent reads.

use std::sync::atomic::{AtomicU64, Ordering};
use std::sync::Arc;
use std::time::Duration;

use mission_executor::{Consumer, MavlinkProjection, TelemetryForwarder};
use shared::models::telemetry::{UavAttitude, UavPosition};
use tokio::time::timeout;

fn pos(lat: i32) -> UavPosition {
    UavPosition {
        lat_e7: lat,
        lon_e7: 0,
        alt_m: 100.0,
        relative_alt_m: 50.0,
        vx_mps: 0.0,
        vy_mps: 0.0,
        vz_mps: 0.0,
        heading_deg: 0.0,
        ts_boot_ms: lat as u32,
    }
}

fn att(yaw: f32) -> UavAttitude {
    UavAttitude {
        roll: 0.0,
        pitch: 0.0,
        yaw,
        rollspeed: 0.0,
        pitchspeed: 0.0,
        yawspeed: 0.0,
        ts_boot_ms: 0,
    }
}

#[tokio::test]
async fn ac1_telemetry_reaches_all_three_consumers() {
    // Arrange — three fast consumers and a producer that publishes
    // 10 alternating position/attitude updates (simulating 10 Hz).
    let f = Arc::new(TelemetryForwarder::new());
    let mut rx_scan = f.subscribe(Consumer::ScanController);
    let mut rx_movement = f.subscribe(Consumer::MovementDetector);
    let mut rx_telemetry = f.subscribe(Consumer::TelemetryStream);

    // Act — publish 10 updates (5 position, 5 attitude).
    for i in 0..10 {
        if i % 2 == 0 {
            f.publish_from_mavlink(&MavlinkProjection::Position(pos(i)));
        } else {
            f.publish_from_mavlink(&MavlinkProjection::Attitude(att(i as f32)));
        }
    }

    // Assert — each consumer received exactly 10 snapshots; the last
    // one carries the latest position and last-set attitude.
    let mut count_scan = 0;
    let mut last_scan = None;
    while let Ok(snap) = rx_scan.try_recv() {
        count_scan += 1;
        last_scan = Some(snap);
    }
    assert_eq!(count_scan, 10);
    let snap = last_scan.unwrap();
    assert_eq!(snap.position.unwrap().lat_e7, 8);
    assert_eq!(snap.attitude.unwrap().yaw, 9.0);

    let count_movement = drain_count(&mut rx_movement);
    let count_telemetry = drain_count(&mut rx_telemetry);
    assert_eq!(count_movement, 10);
    assert_eq!(count_telemetry, 10);

    // No drops on any channel — every consumer kept up.
    for c in Consumer::ALL {
        assert_eq!(f.drop_count(c), 0, "{} drop count should be 0", c.as_str());
    }
}

fn drain_count(rx: &mut mission_executor::DropCountingReceiver) -> usize {
    let mut count = 0;
    while rx.try_recv().is_ok() {
        count += 1;
    }
    count
}

#[tokio::test]
async fn ac2_slow_consumer_drops_fast_consumers_unaffected() {
    // Arrange — channel cap = 4. We publish 16 messages with a slow
    // consumer that waits before reading. The 16 - 4 = 12 oldest
    // messages should be overwritten in its buffer and surface as
    // Lagged(12) on the next recv.
    let f = Arc::new(TelemetryForwarder::with_capacity(4));
    let mut slow = f.subscribe(Consumer::ScanController);
    let mut fast1 = f.subscribe(Consumer::MovementDetector);
    let mut fast2 = f.subscribe(Consumer::TelemetryStream);

    // Spawn fast consumers that drain into local counters as messages arrive.
    let fast1_count = Arc::new(AtomicU64::new(0));
    let fast2_count = Arc::new(AtomicU64::new(0));
    let fast1_count_h = fast1_count.clone();
    let fast2_count_h = fast2_count.clone();
    let fast1_task = tokio::spawn(async move {
        loop {
            match fast1.recv().await {
                Ok(_) => {
                    fast1_count_h.fetch_add(1, Ordering::SeqCst);
                }
                Err(_) => return,
            }
        }
    });
    let fast2_task = tokio::spawn(async move {
        loop {
            match fast2.recv().await {
                Ok(_) => {
                    fast2_count_h.fetch_add(1, Ordering::SeqCst);
                }
                Err(_) => return,
            }
        }
    });

    // Act — publish 16 messages with a tiny yield between each so the
    // fast consumers can keep up while the slow consumer stays
    // un-polled.
    for i in 0..16 {
        f.publish_from_mavlink(&MavlinkProjection::Position(pos(i)));
        tokio::time::sleep(Duration::from_millis(2)).await;
    }

    // Give the fast consumers a moment to flush.
    tokio::time::sleep(Duration::from_millis(50)).await;

    // Slow consumer reads ONE message — recv returns the next not-
    // yet-overwritten value AND the drop counter advances by
    // (16 - cap) under-the-hood.
    let _ = timeout(Duration::from_secs(1), slow.recv()).await.unwrap();

    // Assert — fast consumers saw every message; slow saw drops.
    assert_eq!(fast1_count.load(Ordering::SeqCst), 16);
    assert_eq!(fast2_count.load(Ordering::SeqCst), 16);
    let slow_drops = f.drop_count(Consumer::ScanController);
    assert!(
        slow_drops > 0,
        "expected slow consumer to register some drops, got {slow_drops}"
    );
    // Fast consumers saw zero drops.
    assert_eq!(f.drop_count(Consumer::MovementDetector), 0);
    assert_eq!(f.drop_count(Consumer::TelemetryStream), 0);

    // Cleanup
    fast1_task.abort();
    fast2_task.abort();
    let _ = fast1_task.await;
    let _ = fast2_task.await;
}

#[tokio::test]
async fn ac3_latest_snapshot_is_monotonic_under_concurrent_reads() {
    // Arrange — a producer that publishes 1 000 times in a tight
    // loop, and 4 reader tasks that each take 1 000 snapshots and
    // verify monotonicity in their own observed sequence.
    let f = Arc::new(TelemetryForwarder::new());
    let producer = {
        let f = f.clone();
        tokio::spawn(async move {
            for i in 0..1_000_i32 {
                f.publish_from_mavlink(&MavlinkProjection::Position(pos(i)));
                tokio::task::yield_now().await;
            }
        })
    };

    let mut readers = Vec::new();
    for _ in 0..4 {
        let f = f.clone();
        readers.push(tokio::spawn(async move {
            let mut prev = 0u64;
            for _ in 0..1_000 {
                let snap = f.latest_snapshot();
                assert!(
                    snap.monotonic_ts_ns >= prev,
                    "snapshot regressed: prev={} new={}",
                    prev,
                    snap.monotonic_ts_ns
                );
                prev = snap.monotonic_ts_ns;
                tokio::task::yield_now().await;
            }
        }));
    }

    // Act / Assert — every task must complete without panicking.
    producer.await.unwrap();
    for r in readers {
        r.await.unwrap();
    }

    // Final snapshot must have a non-zero monotonic timestamp.
    assert!(f.last_monotonic_ns() > 0);
}