//! select tests. Beyond the functional cases, the *_stays_precise tests are
//! soundness probes for the consuming-wake protocol: they fire stale loser-
//! arm wakes at an actor and then run a one-shot park (`sleep`, whose early
//! return would be observable as a short elapsed time) to prove the stale
//! wake died at its epoch CAS instead of corrupting the next wait.

use smarm::{channel, run, select, spawn};
use std::sync::atomic::{AtomicI64, Ordering};
use std::time::{Duration, Instant};

static OUT: AtomicI64 = AtomicI64::new(0);

#[test]
fn ready_arm_returns_immediately_without_parking() {
    OUT.store(0, Ordering::SeqCst);
    run(|| {
        let (txa, rxa) = channel::<i64>();
        let (_txb, rxb) = channel::<i64>();
        txa.send(42).unwrap();
        let i = select(&[&rxb, &rxa]);
        assert_eq!(i, 1);
        OUT.store(rxa.try_recv().unwrap().expect("ready arm must hold a message"), Ordering::SeqCst);
    });
    assert_eq!(OUT.load(Ordering::SeqCst), 42);
}

#[test]
fn lower_index_wins_when_several_arms_are_ready() {
    run(|| {
        let (txa, rxa) = channel::<i64>();
        let (txb, rxb) = channel::<i64>();
        txa.send(1).unwrap();
        txb.send(2).unwrap();
        // Documented priority order: index 0 first, regardless of send order.
        assert_eq!(select(&[&rxa, &rxb]), 0);
        assert_eq!(select(&[&rxb, &rxa]), 0);
    });
}

#[test]
fn parks_until_any_arm_fires() {
    OUT.store(0, Ordering::SeqCst);
    run(|| {
        let (txa, _rxa_keepalive) = (channel::<i64>().0, ());
        let _hold = txa; // arm a: sender alive, never sends
        let (txa, rxa) = channel::<i64>();
        let (txb, rxb) = channel::<i64>();
        let _keep_a_open = txa;
        let h = spawn(move || {
            smarm::sleep(Duration::from_millis(10));
            txb.send(7).unwrap();
        });
        let i = select(&[&rxa, &rxb]);
        assert_eq!(i, 1);
        OUT.store(rxb.try_recv().unwrap().unwrap(), Ordering::SeqCst);
        h.join().unwrap();
    });
    assert_eq!(OUT.load(Ordering::SeqCst), 7);
}

#[test]
fn closed_arm_counts_as_ready() {
    run(|| {
        let (_keep, rxa) = channel::<i64>();
        let (txb, rxb) = channel::<i64>();
        drop(txb);
        let i = select(&[&rxa, &rxb]);
        assert_eq!(i, 1);
        // The caller observes the closure on the arm itself.
        assert!(rxb.try_recv().is_err());
    });
}

#[test]
fn closure_while_parked_wakes_the_select() {
    run(|| {
        let (_keep, rxa) = channel::<i64>();
        let (txb, rxb) = channel::<i64>();
        let h = spawn(move || {
            smarm::sleep(Duration::from_millis(10));
            drop(txb);
        });
        assert_eq!(select(&[&rxa, &rxb]), 1);
        assert!(rxb.try_recv().is_err());
        h.join().unwrap();
    });
}

#[test]
fn loser_arm_wake_after_parked_select_stays_precise() {
    // Both arms registered; arm 0 wins the wake; arm 1's sender then fires
    // a wake stamped with the consumed epoch. The subsequent sleep is a
    // one-shot park: an early return would mean the stale wake landed.
    run(|| {
        let (txa, rxa) = channel::<i64>();
        let (txb, rxb) = channel::<i64>();
        let h = spawn(move || {
            smarm::sleep(Duration::from_millis(10));
            txa.send(1).unwrap(); // wins
            txb.send(2).unwrap(); // loser arm: stale-epoch wake
        });
        assert_eq!(select(&[&rxa, &rxb]), 0);
        assert_eq!(rxa.try_recv().unwrap(), Some(1));
        let t0 = Instant::now();
        smarm::sleep(Duration::from_millis(40));
        assert!(
            t0.elapsed() >= Duration::from_millis(40),
            "one-shot park returned early: a stale loser-arm wake landed"
        );
        // The loser's message was never lost.
        assert_eq!(select(&[&rxa, &rxb]), 1);
        assert_eq!(rxb.try_recv().unwrap(), Some(2));
        h.join().unwrap();
    });
}

#[test]
fn no_park_exit_retires_the_wait() {
    // Arm 1 is ready at registration time, so select returns WITHOUT
    // parking while arm 0 holds a live-epoch registration. Arm 0's sender
    // then fires. retire_wait must have invalidated/eaten that wake;
    // the sleep proves it.
    run(|| {
        let (txa, rxa) = channel::<i64>();
        let (txb, rxb) = channel::<i64>();
        txb.send(2).unwrap();
        assert_eq!(select(&[&rxa, &rxb]), 1);
        assert_eq!(rxb.try_recv().unwrap(), Some(2));

        let h = spawn(move || {
            txa.send(1).unwrap(); // fires at the (retired) select epoch
        });
        h.join().unwrap();

        let t0 = Instant::now();
        smarm::sleep(Duration::from_millis(40));
        assert!(
            t0.elapsed() >= Duration::from_millis(40),
            "one-shot park returned early: the no-park exit leaked a wake"
        );
        assert_eq!(rxa.try_recv().unwrap(), Some(1));
    });
}

#[test]
fn select_then_plain_recv_on_a_loser_arm() {
    // A leftover own-registration from a select must not trip the next
    // direct wait on that channel (it is overwritten, not asserted away).
    run(|| {
        let (txa, rxa) = channel::<i64>();
        let (txb, rxb) = channel::<i64>();
        txa.send(1).unwrap();
        assert_eq!(select(&[&rxa, &rxb]), 0); // rxb may keep a registration
        assert_eq!(rxa.try_recv().unwrap(), Some(1));
        let h = spawn(move || {
            smarm::sleep(Duration::from_millis(5));
            txb.send(9).unwrap();
        });
        assert_eq!(rxb.recv().unwrap(), 9);
        h.join().unwrap();
    });
}

#[test]
fn select_loop_drains_two_producers_completely() {
    const N: i64 = 200;
    OUT.store(0, Ordering::SeqCst);
    run(|| {
        let (txa, rxa) = channel::<i64>();
        let (txb, rxb) = channel::<i64>();
        let ha = spawn(move || {
            for v in 0..N {
                txa.send(v).unwrap();
                if v % 7 == 0 {
                    smarm::yield_now();
                }
            }
        });
        let hb = spawn(move || {
            for v in 0..N {
                txb.send(v).unwrap();
                if v % 5 == 0 {
                    smarm::yield_now();
                }
            }
        });
        // A closed arm stays permanently ready, so it must leave the arm
        // set once observed (keeping it would starve the other arm at
        // priority order) — select until the FIRST closure, then drain the
        // survivor with plain recv.
        let mut sum = 0i64;
        let survivor: &smarm::Receiver<i64> = loop {
            let i = select(&[&rxa, &rxb]);
            let arm: &smarm::Receiver<i64> = if i == 0 { &rxa } else { &rxb };
            match arm.try_recv() {
                Ok(Some(v)) => sum += v,
                Ok(None) => {} // defensive: ready arm already drained
                Err(_) => break if i == 0 { &rxb } else { &rxa },
            }
        };
        loop {
            match survivor.recv() {
                Ok(v) => sum += v,
                Err(_) => break,
            }
        }
        OUT.store(sum, Ordering::SeqCst);
        ha.join().unwrap();
        hb.join().unwrap();
    });
    assert_eq!(OUT.load(Ordering::SeqCst), 2 * (0..200i64).sum::<i64>());
}

#[test]
fn motivating_pattern_inbox_plus_monitor_down() {
    // The gen_server/handle_info shape select unlocks: a server waiting on
    // its request inbox AND a monitor Down channel in one park.
    use smarm::monitor;
    run(|| {
        let (req_tx, req_rx) = channel::<i64>();
        let worker = spawn(|| {
            smarm::sleep(Duration::from_millis(10));
            // worker exits -> Down fires
        });
        let m = monitor(worker.pid());
        let _keep_inbox_open = req_tx;

        let mut served = 0;
        loop {
            match select(&[&m.rx, &req_rx]) {
                0 => {
                    let _down = m.rx.try_recv().unwrap().expect("Down message");
                    break;
                }
                _ => {
                    if let Ok(Some(_)) = req_rx.try_recv() {
                        served += 1;
                    }
                }
            }
        }
        assert_eq!(served, 0);
        worker.join().unwrap();
    });
}