//! RFC 016 Chunk 4 — the observer gen_server. The whole file is gated on the
//! `observer` feature (run with `cargo test --features observer`); without it
//! the module does not exist and there is nothing to compile.
//!
//! The point these prove: the observer is *transport over the same reads*. Each
//! verb returns exactly what the corresponding Chunk-1 primitive would, just
//! marshalled over the gen_server call channel — so a known spawned actor that
//! `snapshot()` / `actor_info()` would see is equally visible through the
//! observer.
#![cfg(feature = "observer")]

use smarm::observer::{self, ObserverReply, ObserverRequest};
use smarm::{channel, run, ActorState, SNAPSHOT_FORMAT_VERSION};

#[test]
fn observer_relays_snapshot_tree_and_actor_info() {
    run(|| {
        // A worker parked on an empty gate: a known, stable actor for the
        // observer to find across all three verbs.
        let (ready_tx, ready_rx) = channel::<()>();
        let (gate_tx, gate_rx) = channel::<()>();
        let worker = smarm::spawn(move || {
            ready_tx.send(()).unwrap();
            gate_rx.recv().unwrap();
        });
        ready_rx.recv().unwrap();

        let obs = observer::start();

        // Snapshot: the worker is present, and so is the observer itself — it
        // is a scheduled actor like any other.
        let ObserverReply::Snapshot(snap) = obs.call(ObserverRequest::Snapshot).unwrap() else {
            panic!("Snapshot verb must reply Snapshot");
        };
        assert_eq!(snap.format_version, SNAPSHOT_FORMAT_VERSION);
        assert!(
            snap.actors.iter().any(|a| a.pid == worker.pid()),
            "observer's snapshot should contain the spawned worker"
        );
        assert!(
            snap.actors.iter().any(|a| a.pid == obs.pid()),
            "observer should appear in the snapshot it produced"
        );

        // Tree: same data folded into the parentage forest, same version.
        let ObserverReply::Tree(t) = obs.call(ObserverRequest::Tree).unwrap() else {
            panic!("Tree verb must reply Tree");
        };
        assert_eq!(t.format_version, SNAPSHOT_FORMAT_VERSION);
        fn contains(nodes: &[smarm::TreeNode], pid: smarm::Pid) -> bool {
            nodes
                .iter()
                .any(|n| n.info.pid == pid || contains(&n.children, pid))
        }
        assert!(
            contains(&t.roots, worker.pid()),
            "worker should appear somewhere in the observer's tree"
        );

        // ActorInfo: coherent single-actor view, matching a direct read.
        let ObserverReply::ActorInfo(Some(info)) =
            obs.call(ObserverRequest::ActorInfo(worker.pid())).unwrap()
        else {
            panic!("ActorInfo verb must reply ActorInfo(Some) for a live worker");
        };
        assert_eq!(info.pid, worker.pid());

        gate_tx.send(()).unwrap();
        worker.join().unwrap();
    });
}

#[test]
fn observer_reports_none_for_a_forged_pid() {
    run(|| {
        let obs = observer::start();
        // An index that is not in the slab at all — the verb relays the
        // primitive's `None` faithfully.
        let forged = smarm::Pid::new(u32::MAX - 1, 0);
        let ObserverReply::ActorInfo(none) =
            obs.call(ObserverRequest::ActorInfo(forged)).unwrap()
        else {
            panic!("ActorInfo verb must reply ActorInfo");
        };
        assert!(none.is_none(), "a forged pid should relay as None");
    });
}

#[test]
fn observer_sees_a_parked_actor_as_parked() {
    run(|| {
        let (ready_tx, ready_rx) = channel::<()>();
        let (gate_tx, gate_rx) = channel::<()>();
        let worker = smarm::spawn(move || {
            ready_tx.send(()).unwrap();
            gate_rx.recv().unwrap(); // nothing to do but park on the gate
        });
        ready_rx.recv().unwrap();

        let obs = observer::start();
        // Bounded poll through the observer until the worker reaches Parked —
        // proving the live state classification rides the call channel intact.
        let mut parked = false;
        for _ in 0..100_000 {
            let ObserverReply::ActorInfo(info) =
                obs.call(ObserverRequest::ActorInfo(worker.pid())).unwrap()
            else {
                panic!("ActorInfo verb must reply ActorInfo");
            };
            if matches!(info, Some(i) if i.state == ActorState::Parked) {
                parked = true;
                break;
            }
            smarm::yield_now();
        }
        assert!(parked, "observer should eventually report the worker as Parked");

        gate_tx.send(()).unwrap();
        worker.join().unwrap();
    });
}