//! The live observer (RFC 016 Chunk 4) producing an OTP `observer`-flavoured
//! dump of a running system.
//!
//! Run it with the feature on:
//!
//! ```text
//! cargo run --example observer --features observer
//! ```
//!
//! It stands up a tiny tree — a named service plus two workers parked on a gate
//! — starts the [`observer`](smarm::observer) gen_server, then asks it for a
//! snapshot and a tree over the call channel and renders both. The observer is
//! pure transport: every line below is the Chunk-1 read
//! ([`snapshot`](smarm::snapshot) / [`tree`](smarm::tree)) marshalled across a
//! `call`, nothing more.

use smarm::observer::{self, ObserverReply, ObserverRequest};
use smarm::{channel, register, run, spawn, ActorState, Name, RuntimeSnapshot, RuntimeTree, TreeNode};

const ECHO: Name<u64> = Name::new("echo");

fn state_glyph(s: ActorState) -> &'static str {
    match s {
        ActorState::Queued => "queued",
        ActorState::Running => "running",
        ActorState::Notified => "notified",
        ActorState::Parked => "parked",
        ActorState::Done => "done",
    }
}

/// A `ps`-style table over the flat snapshot.
fn print_snapshot(snap: &RuntimeSnapshot) {
    println!("snapshot (format v{}, {} actors)", snap.format_version, snap.actors.len());
    println!(
        "  {:<10} {:<9} {:<10} {:>4} {:>4} {:>4} {:>4} {:>5}  {}",
        "pid", "state", "parent", "mon", "lnk", "joi", "mbox", "msgs", "names"
    );
    for a in &snap.actors {
        let parent = if a.supervisor.index() == u32::MAX {
            "<root>".to_string()
        } else {
            format!("{}.{}", a.supervisor.index(), a.supervisor.generation())
        };
        println!(
            "  {:<10} {:<9} {:<10} {:>4} {:>4} {:>4} {:>4} {:>5}  {}",
            format!("{}.{}", a.pid.index(), a.pid.generation()),
            state_glyph(a.state),
            parent,
            a.monitors,
            a.links,
            a.joiners,
            a.mailbox_depth,
            a.messages_received,
            if a.names.is_empty() { "-".to_string() } else { a.names.join(",") },
        );
    }
}

/// The parentage forest, indented.
fn print_tree(t: &RuntimeTree) {
    println!("tree (format v{})", t.format_version);
    fn walk(node: &TreeNode, depth: usize) {
        let indent = "  ".repeat(depth + 1);
        let flag = if node.orphaned { " [orphaned]" } else { "" };
        let names = if node.info.names.is_empty() {
            String::new()
        } else {
            format!(" ({})", node.info.names.join(","))
        };
        println!(
            "{indent}{}.{} {}{names}{flag}",
            node.info.pid.index(),
            node.info.pid.generation(),
            state_glyph(node.info.state),
        );
        for child in &node.children {
            walk(child, depth + 1);
        }
    }
    for root in &t.roots {
        walk(root, 0);
    }
}

fn main() {
    run(|| {
        // A named echo service and two anonymous workers, all parked on a gate
        // so the system holds still while we observe it. Each gets its own gate
        // receiver (a Receiver is single-consumer); we keep the senders to
        // release them at the end.
        let (ready_tx, ready_rx) = channel::<()>();
        let mut gates = Vec::new();

        let svc = {
            let (gate_tx, gate_rx) = channel::<()>();
            gates.push(gate_tx);
            let ready_tx = ready_tx.clone();
            spawn(move || {
                let (cmd_tx, cmd_rx) = channel::<u64>();
                register(ECHO, cmd_tx).unwrap();
                ready_tx.send(()).unwrap();
                gate_rx.recv().unwrap();
                drop(cmd_rx);
            })
        };
        let workers: Vec<_> = (0..2)
            .map(|_| {
                let (gate_tx, gate_rx) = channel::<()>();
                gates.push(gate_tx);
                let ready_tx = ready_tx.clone();
                spawn(move || {
                    ready_tx.send(()).unwrap();
                    gate_rx.recv().unwrap();
                })
            })
            .collect();

        // Wait until all three have announced and parked.
        for _ in 0..3 {
            ready_rx.recv().unwrap();
        }
        // Queue two commands at the echo service so its mailbox depth is visible.
        smarm::send(ECHO, 1).unwrap();
        smarm::send(ECHO, 2).unwrap();

        // Start the observer and dump the system through it.
        let obs = observer::start();

        let ObserverReply::Snapshot(snap) = obs.call(ObserverRequest::Snapshot).unwrap() else {
            unreachable!()
        };
        let ObserverReply::Tree(t) = obs.call(ObserverRequest::Tree).unwrap() else {
            unreachable!()
        };

        print_snapshot(&snap);
        println!();
        print_tree(&t);

        // Release everyone and drain.
        for gate_tx in gates {
            gate_tx.send(()).unwrap();
        }
        svc.join().unwrap();
        for w in workers {
            w.join().unwrap();
        }
    });
}