//! 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, TransientKind};
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 claude_has_session(&Coordinator::agent_claude_dir(&logical)) {
                    current_logged_in.insert(logical.clone());
                }
            }

            if seeded {
                emit_crash_transitions(&coord, &prev_running, &current_running);
                emit_login_transitions(
                    &coord,
                    &prev_logged_in,
                    &current_logged_in,
                    &sub_agents,
                    &prev_sub_agents,
                );
            }
            // 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) {
        let active = transients.get(stopped).map(|st| st.kind);
        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::HelperEvent::ContainerCrash {
            agent: stopped.clone(),
            note: Some("container stopped without an operator action".into()),
        });
    }
}

/// Pure classifier: did the operator stop / restart / destroy /
/// rebuild this container, 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 (if any),
/// `recently_cleared` is one whose RAII guard dropped within the
/// grace window.
fn is_deliberate_stop(
    active: Option<TransientKind>,
    recently_cleared: Option<TransientKind>,
) -> bool {
    let is_op_kind = |kind: TransientKind| {
        matches!(
            kind,
            TransientKind::Stopping
                | TransientKind::Restarting
                | TransientKind::Destroying
                | TransientKind::Rebuilding
        )
    };
    active.is_some_and(is_op_kind) || recently_cleared.is_some_and(is_op_kind)
}

fn emit_login_transitions(
    coord: &Coordinator,
    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");
        coord.notify_manager(&hive_sh4re::HelperEvent::LoggedIn {
            agent: agent.clone(),
        });
    }
    // 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");
        coord.notify_manager(&hive_sh4re::HelperEvent::NeedsLogin {
            agent: (*agent).to_owned(),
        });
    }
}

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

    #[test]
    fn deliberate_when_active_transient_is_operator_kind() {
        for kind in [
            TransientKind::Stopping,
            TransientKind::Restarting,
            TransientKind::Destroying,
            TransientKind::Rebuilding,
        ] {
            assert!(is_deliberate_stop(Some(kind), None), "{kind:?}");
        }
    }

    #[test]
    fn deliberate_when_recent_transient_is_operator_kind() {
        // Race repros: lifecycle action completes + drops the guard
        // between two polls. recent_transient catches it.
        for kind in [
            TransientKind::Stopping,
            TransientKind::Restarting,
            TransientKind::Destroying,
            TransientKind::Rebuilding,
        ] {
            assert!(is_deliberate_stop(None, Some(kind)), "{kind:?}");
        }
    }

    #[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_only_spawning_starting() {
        // Spawning/Starting are never paired with a "stopped" transition
        // — they're starts. If we see one alongside a stop, it's
        // unrelated (e.g. just-started container died), still a crash.
        for kind in [TransientKind::Spawning, TransientKind::Starting] {
            assert!(!is_deliberate_stop(Some(kind), None), "{kind:?} active");
            assert!(!is_deliberate_stop(None, Some(kind)), "{kind:?} recent");
        }
    }
}