//! AZ-653 integration tests for the ViewPro A40 transport.
//!
//! Strategy: bring up a fake A40 endpoint on a second `UdpSocket` in
//! the same process; pair it with the transport under test via a
//! pre-bound `peer` address; drive scenarios by scripting the fake's
//! reply behaviour (echo, drop, corrupt CRC).

use std::net::{Ipv4Addr, SocketAddr};
use std::sync::atomic::{AtomicU8, Ordering};
use std::sync::Arc;
use std::time::Duration;

use tokio::net::UdpSocket;
use tokio::sync::Mutex;

use gimbal_controller::{
    build_a1_angles, decode_frame, encode_frame, A40Transport, CameraCommand, FrameId,
    GimbalCommand, GimbalController, ImageSensor,
};
use shared::models::gimbal::GimbalState;

const LOCALHOST: Ipv4Addr = Ipv4Addr::new(127, 0, 0, 1);

fn loopback(port: u16) -> SocketAddr {
    SocketAddr::new(LOCALHOST.into(), port)
}

fn initial_state() -> GimbalState {
    GimbalState {
        yaw: 0.0,
        pitch: 0.0,
        zoom: 1.0,
        ts_monotonic_ns: 0,
        command_in_flight: false,
    }
}

/// Bind a UDP socket on an OS-chosen ephemeral port and return both
/// the socket and the bound address.
async fn bind_ephemeral() -> (Arc<UdpSocket>, SocketAddr) {
    let s = UdpSocket::bind(loopback(0)).await.expect("bind ephemeral");
    let addr = s.local_addr().expect("local_addr");
    (Arc::new(s), addr)
}

/// Helper — minimal fake A40 endpoint. Behaviour is supplied as a
/// closure invoked for every inbound frame.
struct FakeA40 {
    socket: Arc<UdpSocket>,
    addr: SocketAddr,
}

impl FakeA40 {
    async fn bind() -> Self {
        let (socket, addr) = bind_ephemeral().await;
        Self { socket, addr }
    }
}

#[tokio::test]
async fn ac1_crc_round_trip_no_faults() {
    // Arrange — bring up the fake; build a yaw-30 A1 frame; spawn a
    // task that echoes the (well-formed) command back as a
    // T1_F1_B1_D1 reply (the vendor's angle-feedback frame).
    let fake = FakeA40::bind().await;
    let (test_socket, test_addr) = bind_ephemeral().await;
    test_socket.connect(fake.addr).await.expect("connect");

    let fake_socket = fake.socket.clone();
    let echo_task = tokio::spawn(async move {
        let mut buf = [0u8; 128];
        let (n, from) = fake_socket
            .recv_from(&mut buf)
            .await
            .expect("fake recv_from");
        // Validate the incoming A1 frame parses cleanly.
        let inbound = decode_frame(&buf[..n]).expect("inbound decode");
        assert_eq!(inbound.frame_id, FrameId::A1);
        // Reply with T1_F1_B1_D1 (12 bytes of arbitrary feedback
        // payload — content unchecked by the transport).
        let reply = encode_frame(FrameId::T1F1B1D1, &[0; 12], 0).expect("encode reply");
        fake_socket
            .send_to(&reply, from)
            .await
            .expect("fake send_to");
    });

    let (transport, _recv_task) =
        A40Transport::from_socket(test_socket.clone(), fake.addr).expect("from_socket");
    let _ = test_addr;

    let payload = build_a1_angles(30.0, 0.0);

    // Act
    let reply = transport
        .send_with_response(FrameId::A1, &payload, FrameId::T1F1B1D1)
        .await
        .expect("send_with_response");

    // Assert
    assert_eq!(reply.frame_id, FrameId::T1F1B1D1);
    assert_eq!(transport.faults().crc, 0);
    assert_eq!(transport.faults().timeout, 0);

    echo_task.await.expect("echo task");
}

#[tokio::test]
async fn ac2_crc_mismatch_counted_and_dropped() {
    // Arrange — fake echoes a frame whose checksum is one bit off.
    let fake = FakeA40::bind().await;
    let (test_socket, _) = bind_ephemeral().await;
    test_socket.connect(fake.addr).await.expect("connect");

    let fake_socket = fake.socket.clone();
    tokio::spawn(async move {
        let mut buf = [0u8; 128];
        let (_n, from) = fake_socket
            .recv_from(&mut buf)
            .await
            .expect("fake recv_from");
        // Craft a corrupt frame (flip the checksum).
        let mut reply = encode_frame(FrameId::T1F1B1D1, &[0; 12], 0).expect("encode reply");
        let last = reply.len() - 1;
        reply[last] ^= 0x01;
        fake_socket
            .send_to(&reply, from)
            .await
            .expect("fake send_to");
    });

    let (transport, _recv_task) =
        A40Transport::from_socket(test_socket, fake.addr).expect("from_socket");
    let transport = transport
        .with_command_deadline(Duration::from_millis(80))
        .with_max_retries(1);

    let payload = build_a1_angles(30.0, 0.0);

    // Act — must fail (the corrupt frame is dropped; no valid reply
    // arrives within the deadline).
    let result = transport
        .send_with_response(FrameId::A1, &payload, FrameId::T1F1B1D1)
        .await;

    // Assert — CRC counter incremented; timeout counter incremented
    // because no valid reply arrived.
    assert!(
        result.is_err(),
        "expected MaxRetriesExceeded; got {result:?}"
    );
    // The receive loop is asynchronous; give it a tick to record.
    tokio::time::sleep(Duration::from_millis(20)).await;
    let faults = transport.faults();
    assert!(faults.crc >= 1, "expected ≥1 CRC fault, got {}", faults.crc);
    assert!(
        faults.timeout >= 1,
        "expected ≥1 timeout fault, got {}",
        faults.timeout
    );
}

#[tokio::test]
async fn ac3_command_timeout_retries_then_succeeds() {
    // Arrange — fake drops the FIRST inbound frame silently; replies
    // to every subsequent one.
    let fake = FakeA40::bind().await;
    let (test_socket, _) = bind_ephemeral().await;
    test_socket.connect(fake.addr).await.expect("connect");

    let drop_count = Arc::new(AtomicU8::new(0));
    let fake_socket = fake.socket.clone();
    let drop_count_for_task = drop_count.clone();
    tokio::spawn(async move {
        loop {
            let mut buf = [0u8; 128];
            let Ok((_n, from)) = fake_socket.recv_from(&mut buf).await else {
                return;
            };
            let prior = drop_count_for_task.fetch_add(1, Ordering::Relaxed);
            if prior == 0 {
                // Silently drop the first command.
                continue;
            }
            let reply = encode_frame(FrameId::T1F1B1D1, &[0; 12], 0).expect("encode reply");
            let _ = fake_socket.send_to(&reply, from).await;
        }
    });

    let (transport, _recv_task) =
        A40Transport::from_socket(test_socket, fake.addr).expect("from_socket");
    let transport = transport
        .with_command_deadline(Duration::from_millis(80))
        .with_max_retries(3);

    let payload = build_a1_angles(30.0, 0.0);

    // Act
    let reply = transport
        .send_with_response(FrameId::A1, &payload, FrameId::T1F1B1D1)
        .await
        .expect("retry should succeed");

    // Assert — exactly one timeout (first attempt dropped); reply
    // arrived on the second attempt.
    assert_eq!(reply.frame_id, FrameId::T1F1B1D1);
    let faults = transport.faults();
    assert_eq!(
        faults.timeout, 1,
        "expected 1 timeout fault, got {}",
        faults.timeout
    );
    assert_eq!(faults.crc, 0);
    assert!(
        drop_count.load(Ordering::Relaxed) >= 2,
        "fake should have seen ≥2 commands"
    );
}

#[tokio::test]
async fn ac4_cap_exhaustion_returns_max_retries_exceeded() {
    // Arrange — fake never replies. The transport should fail after
    // exactly `max_retries` attempts with `MaxRetriesExceeded`.
    let fake = FakeA40::bind().await;
    let (test_socket, _) = bind_ephemeral().await;
    test_socket.connect(fake.addr).await.expect("connect");

    let attempts_seen = Arc::new(Mutex::new(0u32));
    let fake_socket = fake.socket.clone();
    let attempts_for_task = attempts_seen.clone();
    tokio::spawn(async move {
        loop {
            let mut buf = [0u8; 128];
            let Ok((_, _from)) = fake_socket.recv_from(&mut buf).await else {
                return;
            };
            *attempts_for_task.lock().await += 1;
            // Never reply.
        }
    });

    let (transport, _recv_task) =
        A40Transport::from_socket(test_socket, fake.addr).expect("from_socket");
    let transport = transport
        .with_command_deadline(Duration::from_millis(60))
        .with_max_retries(3);

    let payload = build_a1_angles(30.0, 0.0);

    // Act
    let err = transport
        .send_with_response(FrameId::A1, &payload, FrameId::T1F1B1D1)
        .await
        .expect_err("should hit cap");

    // Assert
    assert!(
        matches!(
            err,
            gimbal_controller::A40Error::MaxRetriesExceeded { attempts: 3, .. }
        ),
        "expected MaxRetriesExceeded(3); got {err:?}"
    );
    let faults = transport.faults();
    assert_eq!(
        faults.timeout, 3,
        "expected 3 timeout faults; got {}",
        faults.timeout
    );
    // Give the fake one final beat to record the final attempt.
    tokio::time::sleep(Duration::from_millis(20)).await;
    let seen = *attempts_seen.lock().await;
    assert_eq!(seen, 3, "fake should have seen exactly 3 attempts");
}

#[tokio::test]
async fn set_pose_via_transport_updates_state_stream() {
    // Arrange — full GimbalController + transport wired together;
    // fake echoes every A1 with a T1_F1_B1_D1 ack.
    let fake = FakeA40::bind().await;
    let (test_socket, _) = bind_ephemeral().await;
    test_socket.connect(fake.addr).await.expect("connect");

    let fake_socket = fake.socket.clone();
    tokio::spawn(async move {
        loop {
            let mut buf = [0u8; 128];
            let Ok((_, from)) = fake_socket.recv_from(&mut buf).await else {
                return;
            };
            let reply = encode_frame(FrameId::T1F1B1D1, &[0; 12], 0).expect("encode reply");
            let _ = fake_socket.send_to(&reply, from).await;
        }
    });

    let (transport, _recv_task) =
        A40Transport::from_socket(test_socket, fake.addr).expect("from_socket");
    let controller = GimbalController::with_transport(initial_state(), transport);
    let handle = controller.handle();
    let mut state_rx = handle.state_stream();

    // Act
    handle
        .set_pose(GimbalCommand {
            yaw_deg: 45.0,
            pitch_deg: -10.0,
        })
        .await
        .expect("set_pose");

    // Assert
    state_rx.changed().await.expect("state changed");
    let snapshot = *state_rx.borrow();
    assert_eq!(snapshot.yaw, 45.0);
    assert_eq!(snapshot.pitch, -10.0);
    assert_eq!(handle.faults().expect("transport present").timeout, 0);
}

#[tokio::test]
async fn zoom_via_transport_updates_zoom_state() {
    // Arrange
    let fake = FakeA40::bind().await;
    let (test_socket, _) = bind_ephemeral().await;
    test_socket.connect(fake.addr).await.expect("connect");

    let fake_socket = fake.socket.clone();
    tokio::spawn(async move {
        loop {
            let mut buf = [0u8; 128];
            let Ok((_, from)) = fake_socket.recv_from(&mut buf).await else {
                return;
            };
            let reply = encode_frame(FrameId::T1F1B1D1, &[0; 12], 0).expect("encode reply");
            let _ = fake_socket.send_to(&reply, from).await;
        }
    });

    let (transport, _recv_task) =
        A40Transport::from_socket(test_socket, fake.addr).expect("from_socket");
    let controller = GimbalController::with_transport(initial_state(), transport);
    let handle = controller.handle();

    // Act
    handle.zoom(4.0).await.expect("zoom");

    // Assert
    let snapshot = handle.state();
    assert_eq!(snapshot.zoom, 4.0);
}

#[tokio::test]
async fn build_c1_camera_payload_matches_vendor_layout() {
    // Arrange + Act
    let payload = gimbal_controller::build_c1_camera(ImageSensor::Eo1, CameraCommand::ZoomIn);

    // Assert — sanity-check the byte layout the transport will send.
    assert_eq!(payload, [0x01, 0x09]);
}