//! Per-container crash and login-state watcher. Polls every managed
//! container on a 10s interval. Fires `ContainerCrash`, `LoggedIn`,
//! and `NeedsLogin` helper events. Event semantics and the
//! `RECENT_TRANSIENT_GRACE` window: `docs/approvals.md::Helper events`.

use std::collections::HashSet;
use std::sync::Arc;
use std::time::Duration;

use crate::container_view::claude_has_session;
use crate::coordinator::Coordinator;
use crate::lifecycle::{self, AGENT_PREFIX};

const POLL_INTERVAL: Duration = Duration::from_secs(10);

/// How long an operator-initiated transient stays "recently cleared"
/// for the purpose of suppressing crash events. Three full
/// `POLL_INTERVAL`s gives the post-lifecycle path comfortable
/// breathing room — the watcher will have polled at least twice
/// inside the window even with worst-case timer skew.
const RECENT_TRANSIENT_GRACE: Duration = Duration::from_secs(30);

pub fn spawn(coord: Arc<Coordinator>) {
    let mut shutdown = coord.shutdown_rx();
    tokio::spawn(async move {
        let mut prev_running: HashSet<String> = HashSet::new();
        let mut prev_logged_in: HashSet<String> = HashSet::new();
        let mut prev_sub_agents: HashSet<String> = HashSet::new();
        let mut seeded = false;
        loop {
            let raw = lifecycle::list().await.unwrap_or_default();
            let mut current_running = HashSet::new();
            let mut current_logged_in = HashSet::new();
            let mut sub_agents: Vec<String> = Vec::new();
            for c in &raw {
                let Some(logical) = c.strip_prefix(AGENT_PREFIX) else {
                    continue;
                };
                let logical = logical.to_owned();
                sub_agents.push(logical.clone());
                if lifecycle::is_running(&logical).await {
                    current_running.insert(logical.clone());
                }
                if hive_types::Ident::parse(&logical)
                    .is_ok_and(|id| claude_has_session(&Coordinator::agent_claude_dir(&id)))
                {
                    current_logged_in.insert(logical.clone());
                }
            }

            if seeded {
                emit_crash_transitions(&coord, &prev_running, &current_running);
                emit_login_transitions(
                    &prev_logged_in,
                    &current_logged_in,
                    &sub_agents,
                    &prev_sub_agents,
                )
                .await;
            }
            // Periodic container rescan — catches state flips that
            // happen outside our mutation surface (operator runs
            // `nixos-container stop` over ssh, agent logs in via its
            // own web UI, etc.) so the dashboard converges within one
            // POLL_INTERVAL. Idempotent + cheap when nothing changed.
            coord.rescan_containers_and_emit().await;
            prev_running = current_running;
            prev_logged_in = current_logged_in;
            prev_sub_agents = sub_agents.into_iter().collect();
            seeded = true;

            tokio::select! {
                () = tokio::time::sleep(POLL_INTERVAL) => {}
                _ = shutdown.changed() => {
                    tracing::info!("crash watcher: shutdown signal received");
                    break;
                }
            }
        }
    });
}

fn emit_crash_transitions(coord: &Coordinator, prev: &HashSet<String>, current: &HashSet<String>) {
    let transients = coord.transient_snapshot();
    // Operator actions whose RAII guard already cleared but only just;
    // suppresses the race where `lifecycle::kill` returns + drops the
    // guard between two crash-watch polls.
    let recent = coord.recent_transient_within(RECENT_TRANSIENT_GRACE);
    for stopped in prev.difference(current) {
        // One source: a running queue node that declared it takes the container
        // down. There used to be a second — an imperative suppression guard for
        // operations with no node behind them — and destroy becoming a DAG
        // removed the last caller, so intent now has exactly one home.
        // `any`, not "the" pill: an agent can have several running nodes at
        // once (a lease-exempt build alongside a lease-holding stop), and it
        // only takes one of them expecting the container down for this to be
        // a deliberate stop rather than a crash.
        let active = transients
            .get(stopped)
            .map(|sts| sts.iter().any(|st| st.takes_container_down));
        let recently_cleared = recent.get(stopped).copied();
        if is_deliberate_stop(active, recently_cleared) {
            continue;
        }
        tracing::warn!(agent = %stopped, "container crash detected");
        coord.record_crash(stopped);
        coord.notify_manager(&hive_sh4re::manager::HelperEvent::ContainerCrash {
            agent: stopped.clone(),
            note: Some("container stopped without an operator action".into()),
        });
    }
}

/// Pure classifier: did an operation take this container down on purpose, or
/// did it crash? Splits the matcher out so it has a focused unit test without
/// needing a Coordinator fixture. `active` is the currently-set transient's
/// `deliberate_stop` (if any), `recently_cleared` is one whose RAII guard
/// dropped within the grace window.
///
/// This reads the flag the transient's creator set and nothing else. It used to
/// match a `TransientKind`, which meant a pill's *display* vocabulary decided a
/// crash-alert question — so renaming or adding a label silently moved the
/// alerting boundary. Whoever starts the operation knows whether the container
/// is meant to go down; nothing downstream can re-derive it.
fn is_deliberate_stop(active: Option<bool>, recently_cleared: Option<bool>) -> bool {
    active.unwrap_or(false) || recently_cleared.unwrap_or(false)
}

async fn emit_login_transitions(
    prev: &HashSet<String>,
    current: &HashSet<String>,
    sub_agents: &[String],
    prev_sub_agents: &HashSet<String>,
) {
    for agent in current.difference(prev) {
        tracing::info!(%agent, "agent logged in");
        crate::swarm_notices::notify(
            "core",
            Some(format!("logged_in:{agent}")),
            format!("agent '{agent}' logged in"),
            None,
        )
        .await;
    }
    // Detect transitions into "needs login": an agent that was previously
    // logged-in goes unsigned (credentials deleted), OR a brand-new agent
    // appears without a session.
    //
    // prev_needs uses prev_sub_agents (the agent set from the last tick) so
    // that a newly-spawned agent — which does not appear in prev_sub_agents —
    // is absent from prev_needs even though it's not in prev_logged_in.
    // Without this, new agents land in both prev_needs and current_needs and
    // the set difference is empty, silently dropping the event.
    let prev_needs: HashSet<&str> = prev_sub_agents
        .iter()
        .map(String::as_str)
        .filter(|n| !prev.contains(*n))
        .collect();
    let current_needs: HashSet<&str> = sub_agents
        .iter()
        .map(String::as_str)
        .filter(|n| !current.contains(*n))
        .collect();
    for agent in current_needs.difference(&prev_needs) {
        tracing::info!(%agent, "agent needs login");
        crate::swarm_notices::notify(
            "core",
            Some(format!("needs_login:{agent}")),
            format!("agent '{agent}' needs login"),
            None,
        )
        .await;
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn deliberate_when_either_source_says_so() {
        // Active guard, and the race repro: a lifecycle action completes and
        // drops its guard between two polls, so only `recent` still carries it.
        assert!(is_deliberate_stop(Some(true), None));
        assert!(is_deliberate_stop(None, Some(true)));
        assert!(is_deliberate_stop(Some(true), Some(true)));
    }

    #[test]
    fn not_deliberate_with_no_transient_at_all() {
        // The real-crash case — fires the ContainerCrash event.
        assert!(!is_deliberate_stop(None, None));
    }

    #[test]
    fn not_deliberate_when_the_operation_was_bringing_the_container_up() {
        // The case that used to be spelled `Spawning` / `Starting`: an
        // operation IS in flight, but it is not one that takes the container
        // down, so a container that vanishes under it really did crash.
        //
        // This is why `deliberate_stop` is carried rather than inferred from
        // the pill — `Create` and `Start` hold the agent's lease exactly like
        // `Stop` does, so "has a pill" cannot answer this.
        assert!(!is_deliberate_stop(Some(false), None));
        assert!(!is_deliberate_stop(None, Some(false)));
        assert!(!is_deliberate_stop(Some(false), Some(false)));
    }
}