use super::*;
use crate::{
    config_client::{ClientEvent, tests::pending_close},
    state::tests::unknown_board,
};
use std::{io, os::fd::FromRawFd, sync::mpsc};

fn pty() -> (File, File, String) {
    let (mut master, mut slave) = (-1, -1);
    // SAFETY: valid out-pointers receive two owned fds. Optional settings are null.
    let opened = unsafe {
        libc::openpty(
            &mut master,
            &mut slave,
            std::ptr::null_mut(),
            std::ptr::null(),
            std::ptr::null(),
        )
    };
    assert_eq!(opened, 0);
    // SAFETY: openpty returned fresh fds whose ownership is transferred once.
    let master = unsafe { File::from_raw_fd(master) };
    // SAFETY: the second fresh fd is distinct and is transferred once.
    let slave = unsafe { File::from_raw_fd(slave) };
    // SAFETY: this live fd accepts the integer flags passed to fcntl.
    let configured = unsafe { libc::fcntl(master.as_raw_fd(), libc::F_SETFL, libc::O_NONBLOCK) };
    assert_eq!(configured, 0);
    let path = format!("/proc/self/fd/{}", slave.as_raw_fd());
    (master, slave, path)
}

fn fill_transmit_queue(file: &mut File) {
    for _ in 0..4096 {
        match file.write(&[0; 4096]) {
            Ok(count) => assert_ne!(count, 0),
            Err(error) if error.kind() == io::ErrorKind::WouldBlock => return,
            Err(error) => panic!("cannot fill PTY: {error}"),
        }
    }
    panic!("PTY transmit queue did not reach its bound")
}

fn stall_frame(session: &mut Session, frame: MavlinkFrame) {
    // PTY line-discipline work can free a little space after the first EAGAIN.
    // Keep filling the unread peer until an actual frame write is backpressured.
    for _ in 0..64 {
        fill_transmit_queue(session.link.as_mut().unwrap());
        write_raw(session, frame).unwrap();
        if !flush_pending(session).unwrap() {
            return;
        }
    }
    panic!("PTY did not backpressure a configuration frame")
}

#[test]
fn queued_save_and_reset_recheck_connection_and_configuration_before_effects() {
    for reconnect in [false, true] {
        for action in [Action::Save, Action::ResetSaved] {
            let state = SharedState::default();
            let connection = state.connected("A".into());
            state.configuration_event(ClientEvent::Configuration(unknown_board()));
            state.edit(401, &serde_json::json!(30)).unwrap();
            let intent = state
                .begin_intent(state.snapshot().context, action.kind())
                .unwrap();
            let (_master, _slave, path) = pty();
            let mut session = Session::new(Principal::new(255, 190));
            session.link = Some(open_serial(&path, SerialBaud::DEFAULT).unwrap());
            session.connection = Some(connection);
            if reconnect {
                state.disconnected(None);
                session.connection = Some(state.connected("B".into()));
            }
            state.configuration_event(ClientEvent::Configuration(unknown_board()));
            let before = state.snapshot();
            handle_command(Command { intent, action }, &mut session, &state);
            assert!(session.outbound.is_none());
            assert!(session.client.target().is_err());
            assert_eq!(state.snapshot().config_revision, before.config_revision);
            assert_eq!(state.snapshot().context, before.context);
            assert_eq!(state.snapshot().path, before.path);
        }
    }
}

#[test]
fn partial_writes_keep_exact_offsets_and_total_deadlines() {
    struct ShortWriter {
        bytes: Vec<u8>,
        stalled: bool,
    }
    impl Write for ShortWriter {
        fn write(&mut self, bytes: &[u8]) -> io::Result<usize> {
            if self.stalled {
                return Err(io::ErrorKind::WouldBlock.into());
            }
            let count = bytes.len().min(3);
            self.bytes.extend_from_slice(&bytes[..count]);
            Ok(count)
        }
        fn flush(&mut self) -> io::Result<()> {
            Ok(())
        }
    }
    let (_, frame) = pending_close();
    let mut pending = PendingWrite {
        frame,
        position: 0,
        deadline: Instant::now() + WRITE_TIMEOUT,
    };
    let mut output = ShortWriter {
        bytes: Vec::new(),
        stalled: false,
    };
    assert!(!pending.advance(&mut output).unwrap());
    output.stalled = true;
    assert!(!pending.advance(&mut output).unwrap());
    assert_eq!(pending.position, 3);
    output.stalled = false;
    for _ in 0..frame.raw_bytes().len() {
        if pending.advance(&mut output).unwrap() {
            break;
        }
    }
    assert_eq!(output.bytes, frame.raw_bytes());
    pending.position = 0;
    pending.deadline = Instant::now();
    assert!(
        pending
            .advance(&mut output)
            .unwrap_err()
            .contains("deadline")
    );
    assert_eq!(output.bytes, frame.raw_bytes());
}

#[test]
fn nonblocking_pty_backpressure_can_be_cancelled_and_shutdown_preserves_close_uncertainty() {
    let (_master, _slave, path) = pty();
    let mut file = open_serial(&path, SerialBaud::DEFAULT).unwrap();
    // SAFETY: fcntl reads flags for this still-owned valid fd.
    let flags = unsafe { libc::fcntl(file.as_raw_fd(), libc::F_GETFL) };
    assert_ne!(flags & libc::O_NONBLOCK, 0);
    fill_transmit_queue(&mut file);
    let state = Arc::new(SharedState::default());
    let connection = state.connected(path);
    state.configuration_event(ClientEvent::Configuration(unknown_board()));
    let (client, frame) = pending_close();
    let mut session = Session::new(Principal::new(255, 190));
    session.client = client;
    session.connection = Some(connection);
    session.link = Some(file);
    let started = Instant::now();
    stall_frame(&mut session, frame);
    assert!(started.elapsed() < Duration::from_millis(100));

    let stopping = Arc::new(AtomicBool::new(false));
    let (commands, receiver) = sync_channel(COMMAND_CAPACITY);
    let worker_state = Arc::clone(&state);
    let worker_stop = Arc::clone(&stopping);
    let worker = thread::spawn(move || worker(receiver, worker_state, session, worker_stop));
    let controller = SerialController {
        commands,
        worker: Mutex::new(Some(worker)),
        baud: SerialBaud::DEFAULT,
        state: Arc::clone(&state),
        stopping,
    };
    let (done, completed) = mpsc::channel();
    let shutdown = thread::spawn(move || {
        drop(controller);
        done.send(()).unwrap();
    });
    completed
        .recv_timeout(Duration::from_millis(500))
        .expect("shutdown must cancel a stalled write");
    shutdown.join().unwrap();
    assert!(state.snapshot().path.is_none());
    assert!(state.snapshot().durable_state_unknown);
    assert!(state.snapshot().error.unwrap().contains("unknown"));
}

#[test]
fn stalled_pty_write_hits_its_deadline_without_blocking_the_worker() {
    let (_master, _slave, path) = pty();
    let mut file = open_serial(&path, SerialBaud::DEFAULT).unwrap();
    fill_transmit_queue(&mut file);
    let mut session = Session::new(Principal::new(255, 190));
    session.link = Some(file);
    let (_, frame) = pending_close();
    stall_frame(&mut session, frame);
    session.outbound.as_mut().unwrap().deadline = Instant::now();
    assert!(
        flush_pending(&mut session)
            .unwrap_err()
            .contains("deadline")
    );
}