//! Startup auto-migration. Six idempotent phases: applied repo,
//! proposed repo, meta repo, container repoint, root→h-root rename,
//! and manager tool-groups backfill.
//! Kill-switch: `HIVE_SKIP_META_MIGRATION=1`. Full migration sequence
//! and phase details: `docs/approvals.md::Migration from the pre-tag`.

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

use anyhow::{Context, Result};
use tokio::process::Command;

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

const KILL_SWITCH: &str = "HIVE_SKIP_META_MIGRATION";

/// Marker for phase 4. Once present, container repoint is skipped on
/// future restarts.
fn repoint_marker() -> PathBuf {
    PathBuf::from("/var/lib/hyperhive/.meta-migration-done")
}

/// Marker for phase 5. Once present, root→h-root container rename is
/// skipped on future restarts.
fn hroot_rename_marker() -> PathBuf {
    PathBuf::from("/var/lib/hyperhive/.hroot-rename-done")
}

/// Substring that identifies the *current* agent flake boilerplate.
/// Bumped whenever the template changes so the startup migration
/// re-renders existing agents onto the new shape. Today the marker
/// is the `flakeInputs` module-arg forwarding line — older templates
/// (raw `import ./agent.nix`) get rewritten on next hive-c0re start.
const MODULE_FLAKE_MARKER: &str = "_module.args.flakeInputs";

pub async fn run(coord: &Arc<Coordinator>) -> Result<()> {
    if std::env::var(KILL_SWITCH).is_ok() {
        tracing::info!("migration: {KILL_SWITCH} set — skipping");
        return Ok(());
    }
    // Stale meta index lock: a previous hive-c0re crash mid-`git add`
    // can leave `.git/index.lock` behind, which blocks every
    // subsequent meta op until somebody `rm`s it manually. We just
    // booted so nothing of ours is holding it; safe to clear.
    let meta_lock = std::path::PathBuf::from("/var/lib/hyperhive/meta/.git/index.lock");
    if meta_lock.exists() {
        match std::fs::remove_file(&meta_lock) {
            Ok(()) => tracing::warn!("cleared stale meta/.git/index.lock"),
            Err(e) => tracing::warn!(error = ?e, "clear stale meta lock failed"),
        }
    }
    let names = enumerate_agents().await;
    tracing::info!(count = names.len(), "migration: scanning");

    // Phase 0: move harness-owned files out of state/ into harness/.
    // Idempotent — rename is a no-op if the source doesn't exist and
    // the destination already does.
    for name in &names {
        migrate_harness_files(name);
    }

    // Phase 1 + 2: per-agent applied + proposed.
    for name in &names {
        if let Err(e) = migrate_applied_repo(name).await {
            tracing::warn!(%name, error = ?e, "migration: applied repo rewrite failed");
        }
        if let Err(e) =
            lifecycle::setup_proposed(&Coordinator::agent_proposed_dir(name), name).await
        {
            tracing::warn!(%name, error = ?e, "migration: setup_proposed failed");
        }
    }

    // Phase 3: meta repo.
    let agents = lifecycle::agents_for_meta_listing()
        .await
        .unwrap_or_default();
    if let Err(e) = meta::sync_agents(&coord.hive_env(), &agents).await {
        tracing::warn!(error = ?e, "migration: meta sync_agents failed");
    }

    // Phase 4: container repoint, guarded by marker.
    if repoint_marker().exists() {
        tracing::debug!("migration: phase 4 marker present, skipping repoint");
        return Ok(());
    }
    let mut all_ok = true;
    for name in &names {
        // Mark Rebuilding so the crash watcher skips this container
        // during the brief stop+start window the nixos-container
        // update activation triggers. Without this, crash_watch
        // would fire ContainerCrash for every agent here and the
        // manager would spuriously try to recover them.
        let guard = coord.transient_guard(name, crate::coordinator::TransientKind::Rebuilding);
        let result = repoint_container(name).await;
        drop(guard);
        if let Err(e) = result {
            tracing::warn!(%name, error = ?e, "migration: container repoint failed");
            all_ok = false;
        }
    }
    if all_ok
        && !names.is_empty()
        && let Err(e) = std::fs::write(repoint_marker(), b"done\n")
    {
        tracing::warn!(error = ?e, "migration: write repoint marker failed");
    }

    // Phase 5: rename `root` nixos-container to `h-root` for naming
    // consistency with sub-agents. Guarded by marker; skipped on
    // fresh installs (conf file absent) and after first successful run.
    rename_manager_container(coord).await;

    // Phase 6: ensure ruth has explicit tool groups so removing the
    // role-based fallback (Role::Manager → MANAGER_DEFAULT) doesn't
    // silently strip her privileged tools on next rebuild.
    backfill_manager_tool_groups(&names);

    Ok(())
}

/// Move harness-owned sqlite/config files out of the agent-visible state dir
/// and into the sibling harness dir. Best-effort: logs warnings but never
/// fails. Idempotent — each file is only moved if present at the old path
/// and absent at the new path.
fn migrate_harness_files(name: &str) {
    const HARNESS_FILES: &[&str] = &[
        "hyperhive-events.sqlite",
        "hyperhive-turn-stats.sqlite",
        "hyperhive-model",
    ];
    let state_dir = Coordinator::agent_notes_dir(name);
    let harness_dir = Coordinator::agent_harness_dir(name);
    if let Err(e) = std::fs::create_dir_all(&harness_dir) {
        tracing::warn!(%name, error = ?e, "migration: create harness dir failed");
        return;
    }
    for file in HARNESS_FILES {
        let src = state_dir.join(file);
        let dst = harness_dir.join(file);
        if !src.exists() || dst.exists() {
            continue;
        }
        match std::fs::rename(&src, &dst) {
            Ok(()) => tracing::info!(%name, %file, "migration: moved to harness dir"),
            Err(e) => {
                tracing::warn!(%name, %file, error = ?e, "migration: move to harness dir failed");
            }
        }
    }
}

/// Phase 5: rename the `root` nixos-container to `h-root` so the
/// manager container name is consistent with the `h-` prefix used by
/// all sub-agents. Idempotent and marker-guarded. Steps:
///
/// 1. Check `/etc/nixos-containers/root.conf` exists (old name present).
/// 2. Stop the `root` container.
/// 3. Copy `root.conf` → `h-root.conf`.
/// 4. Move `/var/lib/nixos-containers/root/` → `h-root/` (if present).
/// 5. `systemctl daemon-reload` so systemd sees the new unit name.
/// 6. `nixos-container start h-root`.
/// 7. Write the done marker.
///
/// Best-effort: logs warnings on failure. A failed rename leaves both
/// conf files present; on the next hive-c0re start the marker is
/// absent so the phase retries.
async fn rename_manager_container(coord: &Arc<Coordinator>) {
    if hroot_rename_marker().exists() {
        return;
    }
    let old_conf = std::path::PathBuf::from("/etc/nixos-containers/root.conf");
    let new_conf = std::path::PathBuf::from("/etc/nixos-containers/h-root.conf");
    if !old_conf.exists() {
        // Fresh install — root container was never created under the old name.
        let _ = std::fs::write(hroot_rename_marker(), b"done\n");
        return;
    }
    if new_conf.exists() {
        // Already renamed (but marker was lost — write it and return).
        tracing::info!("migration phase 5: h-root.conf already present, marking done");
        let _ = std::fs::write(hroot_rename_marker(), b"done\n");
        return;
    }
    tracing::info!("migration phase 5: renaming root container to h-root");
    let _guard = coord.transient_guard(MANAGER_NAME, crate::coordinator::TransientKind::Rebuilding);

    // Stop the old container. Abort if stop fails — continuing with a
    // running `root` and then starting `h-root` risks two manager
    // instances racing for the same broker / state files.
    match Command::new("nixos-container")
        .args(["stop", "root"])
        .status()
        .await
    {
        Ok(s) if s.success() => {}
        Ok(s) => {
            tracing::warn!(status = %s, "migration phase 5: nixos-container stop root failed — aborting");
            return;
        }
        Err(e) => {
            tracing::warn!(error = ?e, "migration phase 5: nixos-container stop root failed — aborting");
            return;
        }
    }

    // Copy conf file.
    if let Err(e) = std::fs::copy(&old_conf, &new_conf) {
        tracing::warn!(error = ?e, "migration phase 5: copy root.conf failed — aborting");
        return;
    }

    // Move rootfs if it exists (may be absent for ephemeral containers).
    let old_rootfs = std::path::PathBuf::from("/var/lib/nixos-containers/root");
    let new_rootfs = std::path::PathBuf::from("/var/lib/nixos-containers/h-root");
    if old_rootfs.exists()
        && !new_rootfs.exists()
        && let Err(e) = std::fs::rename(&old_rootfs, &new_rootfs)
    {
        tracing::warn!(error = ?e, "migration phase 5: rename rootfs failed (non-fatal)");
    }

    // Daemon reload so systemd picks up the new container@h-root unit.
    if let Err(e) = Command::new("systemctl")
        .args(["daemon-reload"])
        .status()
        .await
    {
        tracing::warn!(error = ?e, "migration phase 5: systemctl daemon-reload failed");
    }

    // Start the renamed container.
    if let Err(e) = Command::new("nixos-container")
        .args(["start", "h-root"])
        .status()
        .await
    {
        tracing::warn!(error = ?e, "migration phase 5: nixos-container start h-root failed");
        return;
    }

    tracing::info!("migration phase 5: root container renamed to h-root");
    let _ = std::fs::write(hroot_rename_marker(), b"done\n");
    // Clean up the old conf file so `nixos-container list` doesn't show
    // a stale stopped `root` entry. Best-effort; a failure here is
    // harmless — h-root is already running and the marker is written.
    if let Err(e) = std::fs::remove_file(&old_conf) {
        tracing::warn!(error = ?e, "migration phase 5: remove old root.conf failed (non-fatal)");
    }
}

async fn enumerate_agents() -> Vec<String> {
    let containers = lifecycle::list().await.unwrap_or_default();
    containers
        .into_iter()
        .filter_map(|c| {
            if c == MANAGER_CONTAINER {
                Some(MANAGER_NAME.to_owned())
            } else {
                c.strip_prefix(AGENT_PREFIX).map(str::to_owned)
            }
        })
        .collect()
}

async fn migrate_applied_repo(name: &str) -> Result<()> {
    let dir = Coordinator::agent_applied_dir(name);
    if !dir.join(".git").exists() {
        return Ok(());
    }
    let flake_path = dir.join("flake.nix");
    let cur = std::fs::read_to_string(&flake_path).unwrap_or_default();
    if cur.contains(MODULE_FLAKE_MARKER) {
        return Ok(());
    }
    let want = lifecycle::initial_flake_nix();
    std::fs::write(&flake_path, want).with_context(|| format!("write {}", flake_path.display()))?;
    raw_git(
        &dir,
        &[
            "-c",
            "user.name=c0re",
            "-c",
            "user.email=c0re@hyperhive.local",
            "add",
            "flake.nix",
        ],
    )
    .await?;
    raw_git(
        &dir,
        &[
            "-c",
            "user.name=c0re",
            "-c",
            "user.email=c0re@hyperhive.local",
            "commit",
            "-m",
            "migration: module-only flake",
        ],
    )
    .await?;
    // Relocate deployed/0 to the migration commit so
    // setup_applied's existence check passes.
    raw_git(&dir, &["tag", "-f", "deployed/0", "HEAD"]).await?;
    tracing::info!(%name, "migration: applied repo migrated to module-only flake");
    Ok(())
}

async fn repoint_container(name: &str) -> Result<()> {
    let container = lifecycle::container_name(name);
    let flake_ref = format!("{}#{name}", meta::meta_dir().display());
    let out = Command::new("nixos-container")
        .args(["update", &container, "--flake", &flake_ref])
        .output()
        .await
        .with_context(|| format!("nixos-container update {container}"))?;
    if !out.status.success() {
        anyhow::bail!(
            "nixos-container update {container} exited {}: {}",
            out.status,
            String::from_utf8_lossy(&out.stderr).trim()
        );
    }
    tracing::info!(%name, %container, "migration: container repointed at meta");
    Ok(())
}

/// Phase 6: if ruth is a deployed agent and has no explicit entry in
/// `tool-groups.json`, set her groups to `MANAGER_DEFAULT` (all groups).
/// Idempotent — skips when entry already present. Prevents a silent tool
/// downgrade when upgrading from a build that relied on the manager-flavor
/// fallback in `effective_tool_groups()`.
fn backfill_manager_tool_groups(names: &[String]) {
    if !names.iter().any(|n| n == MANAGER_NAME) {
        return; // ruth not deployed — nothing to backfill
    }
    let existing = tool_groups::groups_for(MANAGER_NAME);
    if !existing.is_empty() {
        tracing::debug!("migration: ruth already has explicit tool groups — skipping backfill");
        return;
    }
    let all_groups: Vec<String> = hive_sh4re::ToolGroup::MANAGER_DEFAULT
        .iter()
        .map(|g| g.as_str().to_owned())
        .collect();
    match tool_groups::set_groups(MANAGER_NAME, &all_groups) {
        Ok(()) => tracing::info!(
            "migration: backfilled ruth's tool groups to MANAGER_DEFAULT (all groups)"
        ),
        Err(e) => tracing::warn!(
            error = ?e,
            "migration: failed to backfill ruth's tool groups — she may lose privileged tools on next rebuild"
        ),
    }
}

async fn raw_git(dir: &Path, args: &[&str]) -> Result<()> {
    let out = lifecycle::git_command()
        .current_dir(dir)
        .args(args)
        .output()
        .await
        .with_context(|| format!("git {} in {}", args.join(" "), dir.display()))?;
    if !out.status.success() {
        anyhow::bail!(
            "git {} failed: {}",
            args.join(" "),
            String::from_utf8_lossy(&out.stderr).trim()
        );
    }
    Ok(())
}