//! Startup auto-update: on `hive-c0re serve` boot, rebuild every known
//! container unconditionally. `nixos-container update` is a no-op at the
//! nix level when nothing changed (same store path), so the cost is low
//! and avoids rev-marker staleness (all agents always need an update pass
//! when any meta commit lands). See `docs/coordinator.md::Auto-update sweep`.

use std::path::{Path, PathBuf};
use std::sync::Arc;

use anyhow::{Context, Result};

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

/// Marker file recording the hyperhive rev a sub-agent's container was last
/// built against. Sibling of `applied/<name>/` (rather than inside it) to
/// keep it out of the applied repo's git history. Uses a leading dot so a
/// glob over `applied/*` doesn't include it.
pub fn rev_marker_path(name: &str) -> PathBuf {
    PathBuf::from(format!("/var/lib/hyperhive/applied/.{name}.hyperhive-rev"))
}

/// Resolve the current rev of `hyperhive_flake`. For a path on disk we
/// canonicalize (following symlinks) so a /etc/hyperhive → /nix/store/...
/// update yields a different string. For anything else we return None.
#[must_use]
pub fn current_flake_rev(hyperhive_flake: &str) -> Option<String> {
    let path = Path::new(hyperhive_flake);
    if !path.exists() {
        return None;
    }
    std::fs::canonicalize(path)
        .ok()
        .map(|p| p.display().to_string())
}

/// Returns true when the applied repo has commits that have not yet been
/// deployed (i.e. the applied HEAD differs from the sha currently locked in
/// meta's flake.lock). This is the semantic the dashboard `needs_update` chip
/// conveys: "there is a config change ready to apply via rebuild."
#[must_use]
pub fn agent_config_pending(name: &str, deployed_sha: Option<&str>) -> bool {
    let applied_head = std::process::Command::new("git")
        .args([
            "-C",
            &format!("/var/lib/hyperhive/applied/{name}"),
            "rev-parse",
            "HEAD",
        ])
        .output()
        .ok()
        .filter(|o| o.status.success())
        .and_then(|o| String::from_utf8(o.stdout).ok())
        .map(|s| s.trim().to_owned());

    match (applied_head.as_deref(), deployed_sha) {
        (Some(head), Some(sha)) => !head.starts_with(sha) && !sha.starts_with(head),
        _ => false,
    }
}

/// Rebuild one sub-agent and refresh its marker. Used by both the startup
/// scanner and the dashboard's manual "update" button so the two paths
/// can't diverge.
///
/// `queue_entry_id` is `Some(id)` when the rebuild was dispatched from
/// the `rebuild_queue` worker (lets the function annotate its phase via
/// `coord.set_queue_step`) and `None` when called directly (e.g. the
/// root-agent migration nudge in `ensure_root_agent`).
pub async fn rebuild_agent(
    coord: &Arc<Coordinator>,
    name: &str,
    current_rev: &str,
    queue_entry_id: Option<u64>,
) -> Result<()> {
    tracing::info!(%name, rev = %current_rev, "rebuild agent");
    let agent_dir = coord
        .ensure_runtime(name)
        .with_context(|| format!("ensure_runtime {name}"))?;
    let hive = coord.hive_env();
    let paths = Coordinator::agent_paths(name, agent_dir);
    // Suppress crash_watch during the stop+start window inside
    // lifecycle::rebuild. Dashboard rebuilds already do this via
    // lifecycle_action; this catches the auto-update scan + any
    // other direct caller.
    let guard = coord.transient_guard(name, crate::coordinator::TransientKind::Rebuilding);
    let result = lifecycle::rebuild(
        name,
        &hive,
        &paths,
        &|step| coord.set_queue_step(queue_entry_id, step),
        &|log_id| {
            if let Some(qid) = queue_entry_id
                && coord.rebuild_queue.set_build_log_id(qid, log_id)
            {
                coord.emit_rebuild_queue_snapshot();
            }
        },
    )
    .await;
    drop(guard);
    match &result {
        Ok(()) => {
            if let Err(e) = std::fs::write(rev_marker_path(name), current_rev) {
                tracing::warn!(%name, error = ?e, "write rev marker failed");
            }
            coord.notify_manager(&hive_sh4re::HelperEvent::Rebuilt {
                agent: name.to_owned(),
                ok: true,
                note: None,
                sha: None,
                tag: None,
            });
            coord.set_queue_step(queue_entry_id, "forge sync");
            // Run the full forge sync on every successful rebuild so
            // the rebuild path is equivalent to the hive-c0re startup
            // sweep: token, config-repo mirror, meta read access, and
            // meta remote are all kept in sync. Recovers missing tokens
            // (e.g. first-spawn seeding failed transiently) without
            // requiring a full hive-c0re restart.
            crate::forge::sync_agent(name, crate::forge::core_token().as_deref()).await;
            // Mirror the matrix side of the startup sweep: if hive-matrix
            // is present, ensure this agent has a registered user + token.
            // Idempotent (skips if token file already exists). Keeps the
            // rebuild path equivalent to the startup sweep for newly-spawned
            // agents that missed ensure_all().
            crate::matrix::sync_agent_standalone(name).await;
            // Wake the agent on its next turn so claude sees a
            // "you were rebuilt — check /state/ for notes, --continue
            // session intact" hint. Covers dashboard rebuild, admin
            // CLI rebuild, auto-update startup scan, and the
            // dashboard's meta-input update path — all of which
            // route through rebuild_agent.
            coord.kick_agent(name, "container rebuilt");
            // Container state (needs_update, deployed_sha) may have
            // shifted — rescan so dashboards drop the "needs update"
            // chip without waiting for the next /api/state poll.
            coord.rescan_containers_and_emit().await;
            // Lock bump → meta-inputs panel needs to re-render.
            crate::dashboard::emit_meta_inputs_snapshot(coord);
        }
        Err(e) => {
            coord.notify_manager(&hive_sh4re::HelperEvent::Rebuilt {
                agent: name.to_owned(),
                ok: false,
                note: Some(format!("{e:#}")),
                sha: None,
                tag: None,
            });
            coord.rescan_containers_and_emit().await;
        }
    }
    result
}

/// Auto-create the manager container on startup if it isn't already there.
/// hive-c0re manages the manager end-to-end: operators no longer declare
/// `containers.h-ruth` in their host NixOS config. Bypasses the approval
/// queue — manager is required infrastructure. Idempotent.
pub async fn ensure_root_agent(coord: &Arc<Coordinator>) -> Result<()> {
    let existing = lifecycle::list().await.unwrap_or_default();
    let current_rev = current_flake_rev(&coord.hyperhive_flake);
    if existing
        .iter()
        .any(|c| c.strip_prefix(AGENT_PREFIX) == Some(MANAGER_NAME))
    {
        // Container exists already. If it predates the unified lifecycle
        // (no applied flake on disk) we must rebuild — otherwise it's
        // running whatever the host-declarative config was at create
        // time, with a wrong systemd unit and port.
        let applied_flake = Coordinator::agent_applied_dir(MANAGER_NAME).join("flake.nix");
        if !applied_flake.exists()
            && let Some(rev) = current_rev.as_ref()
        {
            tracing::warn!(
                "manager container exists but no applied flake — forcing rebuild to migrate"
            );
            let coord_clone = coord.clone();
            if let Err(e) = rebuild_agent(&coord_clone, MANAGER_NAME, rev.as_str(), None).await {
                tracing::warn!(error = ?e, "manager migration rebuild failed");
            }
        } else {
            tracing::debug!("manager container already present");
        }
        return Ok(());
    }
    tracing::info!("manager container missing — spawning");
    let runtime = coord.ensure_runtime(MANAGER_NAME)?;
    let hive = coord.hive_env();
    let paths = Coordinator::agent_paths(MANAGER_NAME, runtime);
    lifecycle::spawn(MANAGER_NAME, &hive, &paths).await?;
    if let Some(rev) = current_rev {
        let _ = std::fs::write(rev_marker_path(MANAGER_NAME), &rev);
    }
    Ok(())
}

/// Sort `names` in-place so parents precede their children in the topology.
/// Uses BFS from root agents (depth 0). Agents absent from `topo` sort last,
/// alphabetically within their tier. Stable within each depth tier.
pub fn topology_sort(
    names: &mut [String],
    topo: &std::collections::BTreeMap<String, Option<String>>,
) {
    use std::collections::{HashMap, VecDeque};
    // Build depth map using owned clones so the borrow on `names` is released
    // before the sort_by mutable borrow.
    let name_set: Vec<String> = names.to_vec();
    let mut depth: HashMap<String, usize> = HashMap::new();
    let mut queue: VecDeque<String> = VecDeque::new();
    // Seed roots: entries with no parent, or names not present in topo at all.
    for name in &name_set {
        if topo.get(name).is_none_or(Option::is_none) {
            depth.insert(name.clone(), 0);
            queue.push_back(name.clone());
        }
    }
    // BFS to assign depths to children.
    while let Some(parent) = queue.pop_front() {
        let d = depth[&parent] + 1;
        for name in &name_set {
            let is_child = topo.get(name).and_then(|p| p.as_deref()) == Some(parent.as_str());
            if is_child && !depth.contains_key(name) {
                depth.insert(name.clone(), d);
                queue.push_back(name.clone());
            }
        }
    }
    names.sort_by(|a, b| {
        let da = depth.get(a).copied().unwrap_or(usize::MAX);
        let db = depth.get(b).copied().unwrap_or(usize::MAX);
        da.cmp(&db).then(a.cmp(b))
    });
}

/// Rebuild every container on startup. Enqueues a `StartupSweep` parent
/// entry (agent = `"hyperhive"`) followed by per-agent `Rebuild` children
/// linked via `parent_id`. The dashboard renders them nested so the operator
/// can see at a glance "boot N agents, here is each rebuild's status".
/// Returns Ok even if some rebuilds failed.
pub async fn run(coord: Arc<Coordinator>) -> Result<()> {
    let containers = match lifecycle::list().await {
        Ok(c) => c,
        Err(e) => {
            tracing::warn!(error = ?e, "auto-update: nixos-container list failed");
            return Ok(());
        }
    };

    // Enqueue the parent sweep entry. The worker processes it trivially
    // (no-op dispatch) so it completes quickly; its purpose is to give the
    // dashboard a "why" header for the per-agent child rebuilds below.
    let sweep_id = coord.rebuild_queue.enqueue(
        crate::rebuild_queue::QueueKind::StartupSweep,
        "hyperhive".to_owned(),
        crate::rebuild_queue::QueueSource::AutoUpdate,
        format!("startup sweep ({} containers)", containers.len()),
        None,
    );

    tracing::info!(
        agents = containers.len(),
        sweep_id,
        "auto-update: queueing all on startup"
    );

    // Resolve container names to logical agent names, then sort by
    // topology depth so parents are always rebuilt before their
    // children. Root agents (depth 0) go first; agents absent from
    // the topology file sort last (stable, alphabetical within tier).
    let mut logical_names: Vec<String> = containers
        .iter()
        .filter_map(|c| c.strip_prefix(AGENT_PREFIX).map(str::to_owned))
        .collect();
    let topo = crate::topology::read();
    topology_sort(&mut logical_names, &topo);
    for name in logical_names {
        coord.rebuild_queue.enqueue(
            crate::rebuild_queue::QueueKind::Rebuild,
            name,
            crate::rebuild_queue::QueueSource::StartupSweep,
            "startup sweep".to_owned(),
            Some(sweep_id),
        );
    }
    coord.emit_rebuild_queue_snapshot();
    Ok(())
}