//! Per-container state watcher. Polls every managed container on a
//! fixed interval, tracks two orthogonal state-sets across ticks,
//! and emits a `HelperEvent` to the manager on each transition:
//!
//! - **running**: container is up. running → stopped without an
//!   operator-initiated transient (`Stopping` / `Restarting` /
//!   `Destroying` / `Rebuilding`) → `ContainerCrash`.
//! - **logged-in**: claude session dir is populated. ! → ✓ →
//!   `LoggedIn`; ✓ → ! → `NeedsLogin` (rare — usually only fires
//!   on a fresh spawn / purge).
//!
//! `NeedsUpdate` events are now fired from the apply-commit path
//! directly rather than via rev-marker polling (issue #179 cleanup).
//!
//! D-Bus subscription would be lower-latency for the first axis,
//! but polling is simpler and a 10s detection delay is fine.

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, MANAGER_NAME};

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

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 logical = if c == MANAGER_NAME {
                    MANAGER_NAME.to_owned()
                } else if let Some(n) = c.strip_prefix(AGENT_PREFIX) {
                    n.to_owned()
                } else {
                    continue;
                };
                if logical != MANAGER_NAME {
                    sub_agents.push(logical.clone());
                }
                if lifecycle::is_running(&logical).await {
                    current_running.insert(logical.clone());
                }
                if logical != MANAGER_NAME
                    && 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();
    for stopped in prev.difference(current) {
        let deliberate = transients.get(stopped).is_some_and(|st| {
            matches!(
                st.kind,
                TransientKind::Stopping
                    | TransientKind::Restarting
                    | TransientKind::Destroying
                    | TransientKind::Rebuilding
            )
        });
        if deliberate {
            continue;
        }
        tracing::warn!(agent = %stopped, "container crash detected");
        coord.notify_manager(&hive_sh4re::HelperEvent::ContainerCrash {
            agent: stopped.clone(),
            note: Some("container stopped without an operator action".into()),
        });
    }
}

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(),
        });
    }
}