//! `nixos-container` lifecycle + per-agent config flake generation.

use std::path::Path;

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

/// Sub-agent container prefix. `nixos-container` caps the total container name
/// at 11 chars (it gets encoded into network interface names), so the agent
/// name itself can be at most `MAX_AGENT_NAME` chars.
pub const AGENT_PREFIX: &str = "h-";
pub const MAX_AGENT_NAME: usize = 9;
/// Container name of the manager. Lives in the same path scheme as sub-agents
/// (`/var/lib/hyperhive/agents/hm1nd/`, `/var/lib/hyperhive/applied/hm1nd/`),
/// but its container has no `h-` prefix and extends a different
/// nixosConfiguration (`manager`, not `agent-base`).
pub const MANAGER_NAME: &str = "hm1nd";

/// Web UI port reserved for the manager (sub-agents hash into 8100..8999).
pub const MANAGER_PORT: u16 = 8000;

/// Mount point of the per-agent runtime directory inside the container.
pub const CONTAINER_RUNTIME_MOUNT: &str = "/run/hive";

/// Mount point of the per-agent Claude credentials dir inside the container.
/// Persistent across destroy/recreate so OAuth login survives.
pub const CONTAINER_CLAUDE_MOUNT: &str = "/root/.claude";

/// Mount point of the per-agent durable knowledge dir inside the container.
/// Agents are told (system prompt) to keep `notes.md` and any other scratch
/// state here; persists across destroy/recreate.
pub const CONTAINER_NOTES_MOUNT: &str = "/state";

const GIT_NAME: &str = "hive-c0re";
const GIT_EMAIL: &str = "hive-c0re@hyperhive";

/// Sub-agent web UI port range. Deterministic from the agent's name (FNV-1a
/// hash mod range size), so the dashboard can compute the same port without
/// asking hive-c0re.
const WEB_PORT_BASE: u16 = 8100;
const WEB_PORT_RANGE: u16 = 900;

/// Default resource caps applied to every managed container via a systemd
/// drop-in under `/run/systemd/system/container@<NAME>.service.d/`.
const DEFAULT_MEMORY_MAX: &str = "2G";
const DEFAULT_CPU_QUOTA: &str = "50%";

/// Per-agent web UI port. Manager is fixed at `MANAGER_PORT`; every
/// sub-agent is `WEB_PORT_BASE + FNV-1a(name) % WEB_PORT_RANGE`,
/// pure and reproducible from just the name. Collisions are
/// possible (birthday paradox at ~30 agents); the operator resolves
/// them by renaming an agent (different hash → different port).
/// Stable across hosts, restarts, and dashboard renders — no
/// state-file dance.
#[must_use]
pub fn agent_web_port(name: &str) -> u16 {
    if name == MANAGER_NAME {
        return MANAGER_PORT;
    }
    let mut hash: u32 = 2_166_136_261;
    for b in name.bytes() {
        hash ^= u32::from(b);
        hash = hash.wrapping_mul(16_777_619);
    }
    // Modulo of a u32 by a u16's value is guaranteed < u16::MAX, so try_from never fails.
    WEB_PORT_BASE + u16::try_from(hash % u32::from(WEB_PORT_RANGE)).unwrap_or(0)
}

#[must_use]
pub fn container_name(name: &str) -> String {
    if name == MANAGER_NAME {
        MANAGER_NAME.to_owned()
    } else {
        format!("{AGENT_PREFIX}{name}")
    }
}

#[must_use]
pub fn is_manager(name: &str) -> bool {
    name == MANAGER_NAME
}

fn validate(name: &str) -> Result<()> {
    if name.is_empty() {
        bail!("agent name must not be empty");
    }
    if is_manager(name) {
        return Ok(());
    }
    if name.len() > MAX_AGENT_NAME {
        bail!(
            "agent name '{name}' is too long ({} chars); max {MAX_AGENT_NAME}",
            name.len()
        );
    }
    Ok(())
}

/// First name (≠ `self_name`) currently running whose hashed port
/// matches this agent's. The harness inside the colliding container
/// would otherwise loop on `AddrInUse` forever; we surface the
/// conflict here so spawn / rebuild fails loudly with an actionable
/// message instead.
async fn port_collision(self_name: &str) -> Option<String> {
    let port = agent_web_port(self_name);
    let raw = list().await.unwrap_or_default();
    for c in raw {
        let other = if c == MANAGER_NAME {
            MANAGER_NAME.to_owned()
        } else if let Some(n) = c.strip_prefix(AGENT_PREFIX) {
            n.to_owned()
        } else {
            continue;
        };
        if other == self_name {
            continue;
        }
        if agent_web_port(&other) == port && is_running(&other).await {
            return Some(other);
        }
    }
    None
}

#[allow(clippy::too_many_arguments)]
pub async fn spawn(
    name: &str,
    hyperhive_flake: &str,
    agent_dir: &Path,
    proposed_dir: &Path,
    applied_dir: &Path,
    claude_dir: &Path,
    notes_dir: &Path,
    dashboard_port: u16,
) -> Result<()> {
    validate(name)?;
    if let Some(other) = port_collision(name).await {
        bail!(
            "port {} is already taken by '{other}' — rename one of them and retry",
            agent_web_port(name)
        );
    }
    setup_proposed(proposed_dir, name).await?;
    setup_applied(applied_dir, Some(proposed_dir), name).await?;
    ensure_claude_dir(claude_dir)?;
    ensure_state_dir(notes_dir)?;
    // Meta flake gets the new agent's input + nixosConfiguration
    // before `nixos-container create` so the `--flake meta#<name>`
    // ref resolves.
    let agents = agents_after_spawn(name).await?;
    crate::meta::sync_agents(hyperhive_flake, dashboard_port, &agents).await?;
    let container = container_name(name);
    let flake_ref = format!("{}#{name}", crate::meta::meta_dir().display());
    run(&["create", &container, "--flake", &flake_ref]).await?;
    set_nspawn_flags(&container, agent_dir, claude_dir, notes_dir)?;
    set_resource_limits(&container)?;
    systemd_daemon_reload().await?;
    run(&["start", &container]).await
}

/// Build the `AgentSpec` list for the meta flake from `nixos-container
/// list` + a hypothetical extra name not yet in the list (for spawn
/// where the new agent's container doesn't exist yet). Pass empty
/// `name_to_add` from rebuild paths where the agent is already in the
/// container list.
async fn agents_for_meta(name_to_add: Option<&str>) -> Result<Vec<crate::meta::AgentSpec>> {
    let containers = list().await.unwrap_or_default();
    let mut out: Vec<crate::meta::AgentSpec> = containers
        .into_iter()
        .filter_map(|c| {
            let (name, is_manager) = if c == MANAGER_NAME {
                (MANAGER_NAME.to_owned(), true)
            } else if let Some(n) = c.strip_prefix(AGENT_PREFIX) {
                (n.to_owned(), false)
            } else {
                return None;
            };
            Some(crate::meta::AgentSpec {
                port: agent_web_port(&name),
                name,
                is_manager,
            })
        })
        .collect();
    if let Some(extra) = name_to_add
        && !out.iter().any(|a| a.name == extra)
    {
        out.push(crate::meta::AgentSpec {
            name: extra.to_owned(),
            is_manager: is_manager(extra),
            port: agent_web_port(extra),
        });
    }
    out.sort_by(|a, b| a.name.cmp(&b.name));
    Ok(out)
}

async fn agents_after_spawn(name: &str) -> Result<Vec<crate::meta::AgentSpec>> {
    agents_for_meta(Some(name)).await
}

/// Public enumeration of currently-existing agents (whatever
/// `nixos-container list` says), sorted, no extras. For callers
/// outside this module that need to reseed meta after lifecycle
/// changes — destroy, startup reconciliation, etc.
pub async fn agents_for_meta_listing() -> Result<Vec<crate::meta::AgentSpec>> {
    agents_for_meta(None).await
}

pub async fn kill(name: &str) -> Result<()> {
    validate(name)?;
    let container = container_name(name);
    run(&["stop", &container]).await
}

pub async fn start(name: &str) -> Result<()> {
    validate(name)?;
    let container = container_name(name);
    run(&["start", &container]).await
}

/// Stop + start without regenerating any config. For "kick the container"
/// without touching the flake or nspawn flags.
pub async fn restart(name: &str) -> Result<()> {
    kill(name).await?;
    start(name).await
}

/// True when the container's systemd unit is active. Used by the dashboard
/// to gate stop/restart buttons.
pub async fn is_running(name: &str) -> bool {
    let container = container_name(name);
    let unit = format!("container@{container}.service");
    Command::new("systemctl")
        .args(["is-active", "--quiet", &unit])
        .status()
        .await
        .map(|s| s.success())
        .unwrap_or(false)
}

/// Fully tear down a sub-agent's container: stop + remove via `nixos-container
/// destroy`, then clean our own systemd drop-in. Leaves it to the caller to
/// wipe `/var/lib/hyperhive/...` state and the per-agent runtime dir.
pub async fn destroy(name: &str) -> Result<()> {
    validate(name)?;
    let container = container_name(name);
    // nixos-container destroy handles stop + removal of /var/lib/nixos-containers/<C>
    // and /etc/nixos-containers/<C>.conf. Tolerate "no such container".
    if let Err(e) = run(&["destroy", &container]).await {
        tracing::warn!(error = ?e, "nixos-container destroy returned an error; continuing cleanup");
    }
    let dropin_dir = format!("/run/systemd/system/container@{container}.service.d");
    if std::path::Path::new(&dropin_dir).exists() {
        std::fs::remove_dir_all(&dropin_dir).with_context(|| format!("remove {dropin_dir}"))?;
    }
    Ok(())
}

pub async fn rebuild(
    name: &str,
    hyperhive_flake: &str,
    agent_dir: &Path,
    applied_dir: &Path,
    claude_dir: &Path,
    notes_dir: &Path,
    dashboard_port: u16,
) -> Result<()> {
    // Sync the meta flake (idempotent — no-op when the rendered
    // flake matches disk) so a manual rebuild from the dashboard
    // can also recover from a divergent meta repo (e.g. an agent
    // got added directly via `nixos-container create` outside
    // hive-c0re).
    let agents = agents_for_meta(None).await?;
    crate::meta::sync_agents(hyperhive_flake, dashboard_port, &agents).await?;
    // Then bump just this agent's input — picks up whatever
    // `applied/<n>/main` currently points at (deployed/<latest>).
    // Commits the lock if it changed.
    crate::meta::lock_update_for_rebuild(name).await?;
    rebuild_no_meta(name, agent_dir, applied_dir, claude_dir, notes_dir).await
}

/// Container-level rebuild without touching the meta repo. Callers
/// that own the meta side themselves (`actions::run_apply_commit`
/// drives meta through the two-phase prepare/finalize/abort flow)
/// use this directly. Public `rebuild` wraps it with idempotent meta
/// sync + lock-bump-and-commit.
pub async fn rebuild_no_meta(
    name: &str,
    agent_dir: &Path,
    applied_dir: &Path,
    claude_dir: &Path,
    notes_dir: &Path,
) -> Result<()> {
    validate(name)?;
    if let Some(other) = port_collision(name).await {
        bail!(
            "port {} is already taken by '{other}' — rename one of them and retry",
            agent_web_port(name)
        );
    }
    setup_applied(applied_dir, None, name).await?;
    ensure_claude_dir(claude_dir)?;
    ensure_state_dir(notes_dir)?;
    let container = container_name(name);
    let flake_ref = format!("{}#{name}", crate::meta::meta_dir().display());
    set_nspawn_flags(&container, agent_dir, claude_dir, notes_dir)?;
    set_resource_limits(&container)?;
    systemd_daemon_reload().await?;
    run(&["update", &container, "--flake", &flake_ref]).await?;
    // Restart so any nspawn-level changes (bind mounts, networking, etc.) apply.
    run(&["stop", &container]).await?;
    run(&["start", &container]).await
}

pub async fn list() -> Result<Vec<String>> {
    let out = Command::new("nixos-container")
        .arg("list")
        .output()
        .await
        .context("invoke nixos-container list")?;
    if !out.status.success() {
        bail!(
            "nixos-container list exited with status {}: {}",
            out.status,
            String::from_utf8_lossy(&out.stderr).trim()
        );
    }
    Ok(String::from_utf8_lossy(&out.stdout)
        .lines()
        .map(str::trim)
        .filter(|line| line.starts_with(AGENT_PREFIX) || *line == MANAGER_NAME)
        .map(str::to_owned)
        .collect())
}

/// Initialize the manager-editable proposed repo. Seeds two tracked
/// files: `agent.nix` (the module the manager edits) and `flake.nix`
/// (the boilerplate that lets the meta flake import this repo as an
/// input — meta locks at a specific sha and reads
/// `nixosModules.default`, so `flake.nix` must be in the commit). The
/// manager shouldn't edit `flake.nix` (the prompt says so) but it's
/// visible so they can introspect.
///
/// Touched by hive-c0re only on first spawn — never again — so the
/// manager can't be surprised by hive-c0re commits or working-tree
/// resets.
pub async fn setup_proposed(proposed_dir: &Path, name: &str) -> Result<()> {
    let fresh = !proposed_dir.join(".git").exists();
    if fresh {
        std::fs::create_dir_all(proposed_dir)
            .with_context(|| format!("create {}", proposed_dir.display()))?;
        let agent_path = proposed_dir.join("agent.nix");
        if !agent_path.exists() {
            std::fs::write(&agent_path, initial_agent_nix(name))
                .with_context(|| format!("write {}", agent_path.display()))?;
        }
        let flake_path = proposed_dir.join("flake.nix");
        if !flake_path.exists() {
            std::fs::write(&flake_path, initial_flake_nix())
                .with_context(|| format!("write {}", flake_path.display()))?;
        }
        git(proposed_dir, &["init", "--initial-branch=main"]).await?;
        git(proposed_dir, &["add", "agent.nix", "flake.nix"]).await?;
        git_commit(proposed_dir, "hive-c0re init").await?;
    }
    // Idempotently wire the `applied` remote — purely for the
    // manager's ergonomics. The URL is the path inside the manager
    // container (`/applied/<n>/.git`), where the RO bind in
    // `set_nspawn_flags` makes it real. hive-c0re itself never
    // dereferences this remote; the host-side fetch in
    // `request_apply_commit` uses absolute host paths.
    ensure_applied_remote(proposed_dir, name).await
}

async fn ensure_applied_remote(proposed_dir: &Path, name: &str) -> Result<()> {
    let want = format!("/applied/{name}/.git");
    let existing = git_command()
        .current_dir(proposed_dir)
        .args(["remote", "get-url", "applied"])
        .output()
        .await
        .with_context(|| format!("git remote get-url applied in {}", proposed_dir.display()))?;
    if existing.status.success() {
        let current = String::from_utf8_lossy(&existing.stdout).trim().to_owned();
        if current == want {
            return Ok(());
        }
        // URL drifted (path scheme changed, etc.) — re-point it.
        return git(proposed_dir, &["remote", "set-url", "applied", &want]).await;
    }
    git(proposed_dir, &["remote", "add", "applied", &want]).await
}

/// Set up the applied repo. First-spawn only: init the repo, pull
/// proposed's initial commit in via `git fetch`, tag it `deployed/0`.
/// This is the *only* time hive-c0re reads from `proposed` for an
/// agent — subsequent proposals are fetched at `request_apply_commit`
/// time and tagged `proposal/<id>` (see `actions::approve` for the
/// tag state machine).
///
/// `proposed_dir` is `None` on rebuild paths where the repo already
/// exists — we just verify it's the right shape and bail otherwise.
/// Unlike the pre-overhaul code path, `flake.nix` is no longer
/// regenerated at the host level: it's tracked in proposed (seeded by
/// `setup_proposed`) and rides along on every fetch.
pub async fn setup_applied(
    applied_dir: &Path,
    proposed_dir: Option<&Path>,
    name: &str,
) -> Result<()> {
    std::fs::create_dir_all(applied_dir)
        .with_context(|| format!("create {}", applied_dir.display()))?;

    if !applied_dir.join(".git").exists() {
        let Some(proposed) = proposed_dir else {
            bail!(
                "applied repo at {} is missing its .git directory; \
                 cannot rebuild without a proposed source to seed from. \
                 destroy --purge and re-spawn this agent.",
                applied_dir.display()
            );
        };
        git(applied_dir, &["init", "--initial-branch=main"]).await?;
        let proposed_str = proposed.display().to_string();
        git(
            applied_dir,
            &["fetch", "--no-tags", &proposed_str, "main:refs/heads/main"],
        )
        .await?;
        git_read_tree_reset(applied_dir, "refs/heads/main").await?;
        git_tag(applied_dir, "deployed/0", "refs/heads/main").await?;
    } else if git_rev_parse(applied_dir, "refs/tags/deployed/0")
        .await
        .is_err()
    {
        // Pre-overhaul applied repo — no deployed/* tag scheme,
        // flake.nix may be untracked, agent.nix possibly authored by
        // hive-c0re directly. The startup auto-migration fixes this
        // in place; if it didn't run (or got skipped), surface a
        // clear error.
        bail!(
            "applied repo at {} predates the meta-flake layout. \
             Restart hive-c0re to let the auto-migration run, or \
             destroy --purge {name} and re-spawn.",
            applied_dir.display()
        );
    }
    Ok(())
}

/// Create the per-agent Claude credentials dir if missing. Mode 0700 — only
/// root inside the container reads/writes it. Idempotent: existing dirs are
/// left untouched (an agent's OAuth tokens survive `destroy`/recreate).
fn ensure_claude_dir(claude_dir: &Path) -> Result<()> {
    if !claude_dir.exists() {
        std::fs::create_dir_all(claude_dir)
            .with_context(|| format!("create {}", claude_dir.display()))?;
        #[cfg(unix)]
        {
            use std::os::unix::fs::PermissionsExt;
            std::fs::set_permissions(claude_dir, std::fs::Permissions::from_mode(0o700))
                .with_context(|| format!("chmod {}", claude_dir.display()))?;
        }
    }
    Ok(())
}

fn ensure_state_dir(notes_dir: &Path) -> Result<()> {
    if !notes_dir.exists() {
        std::fs::create_dir_all(notes_dir)
            .with_context(|| format!("create {}", notes_dir.display()))?;
    }
    Ok(())
}

fn initial_agent_nix(name: &str) -> String {
    format!(
        "{{ config, pkgs, lib, ... }}:\n{{\n  # Per-agent overrides for {name}. This is a regular NixOS module\n  # — add packages, services, modules, imports as needed.\n  #\n  # imports = [ ./extra-module.nix ];\n  # environment.systemPackages = with pkgs; [ ];\n}}\n",
    )
}

/// Module-only flake exposed by every agent's repo. Consumed by the
/// hive-c0re-owned meta flake at `/var/lib/hyperhive/meta/` as a flake
/// input. Identity injection (`HIVE_PORT` / `HIVE_LABEL` / dashboard
/// port / git committer) lives in the meta flake's wrapper, not here.
pub fn initial_flake_nix() -> &'static str {
    "{\n  description = \"hyperhive agent\";\n  inputs = { };\n  outputs = { self }: {\n    nixosModules.default = import ./agent.nix;\n  };\n}\n"
}

async fn git_commit(dir: &Path, message: &str) -> Result<()> {
    git(
        dir,
        &[
            "-c",
            &format!("user.name={GIT_NAME}"),
            "-c",
            &format!("user.email={GIT_EMAIL}"),
            "commit",
            "-m",
            message,
        ],
    )
    .await
}

/// Spawn `git` honoring the `HYPERHIVE_GIT` env var (absolute path baked in
/// by the NixOS module), falling back to bare `git` (PATH lookup) otherwise.
#[must_use]
pub fn git_command() -> Command {
    let exe = std::env::var("HYPERHIVE_GIT").unwrap_or_else(|_| "git".into());
    Command::new(exe)
}

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

/// Fetch `sha` from the `src` git repo into `dst` and pin it as
/// `refs/tags/<tag>`. Used at `request_apply_commit` time so hive-c0re
/// captures an immutable handle on the manager's commit; subsequent
/// amendments / force-pushes in `src` no longer affect what gets
/// built. Returns the resolved sha (which equals `sha` on success
/// but normalised — short shas get expanded).
pub async fn git_fetch_to_tag(dst: &Path, src: &Path, sha: &str, tag: &str) -> Result<String> {
    let src_str = src.display().to_string();
    let refspec = format!("{sha}:refs/tags/{tag}");
    git(dst, &["fetch", "--no-tags", &src_str, &refspec]).await?;
    git_rev_parse(dst, &format!("refs/tags/{tag}")).await
}

/// Resolve `refname` (a tag, branch, or sha) in `dir` to its full sha.
pub async fn git_rev_parse(dir: &Path, refname: &str) -> Result<String> {
    let out = git_command()
        .current_dir(dir)
        .args(["rev-parse", refname])
        .output()
        .await
        .with_context(|| format!("git rev-parse {refname} in {}", dir.display()))?;
    if !out.status.success() {
        bail!(
            "git rev-parse {refname} failed ({}): {}",
            out.status,
            String::from_utf8_lossy(&out.stderr).trim()
        );
    }
    Ok(String::from_utf8_lossy(&out.stdout).trim().to_owned())
}

/// Plant a lightweight tag at `target`. Errors if the tag already
/// exists — we want loud failures on id reuse, not silent
/// overwrites.
pub async fn git_tag(dir: &Path, name: &str, target: &str) -> Result<()> {
    git(dir, &["tag", name, target]).await
}

/// Plant an annotated tag with `body` as the message. Used for
/// `failed/<id>` (body = build error) and `denied/<id>` (body =
/// operator note). Multi-line bodies handled via stdin so we don't
/// have to escape anything.
pub async fn git_tag_annotated(dir: &Path, name: &str, target: &str, body: &str) -> Result<()> {
    use tokio::io::AsyncWriteExt;
    let mut child = git_command()
        .current_dir(dir)
        .args(["tag", "-a", name, target, "-F", "-"])
        .stdin(std::process::Stdio::piped())
        .stdout(std::process::Stdio::piped())
        .stderr(std::process::Stdio::piped())
        .spawn()
        .with_context(|| format!("spawn git tag -a {name} in {}", dir.display()))?;
    if let Some(mut stdin) = child.stdin.take() {
        stdin
            .write_all(body.as_bytes())
            .await
            .context("write tag body to git stdin")?;
        // Drop closes stdin so git can finish reading.
        drop(stdin);
    }
    let out = child.wait_with_output().await.context("wait git tag -a")?;
    if !out.status.success() {
        bail!(
            "git tag -a {name} failed ({}): {}",
            out.status,
            String::from_utf8_lossy(&out.stderr).trim()
        );
    }
    Ok(())
}

/// Replace working tree + index with the tree at `target` without
/// moving HEAD. `applied/main` stays pointing at the last known-good
/// `deployed/*` while we let `nixos-container update` evaluate the
/// candidate. On build failure callers reset back to HEAD; on
/// success they fast-forward main to `target`.
pub async fn git_read_tree_reset(dir: &Path, target: &str) -> Result<()> {
    git(dir, &["read-tree", "--reset", "-u", target]).await
}

/// Hard-set a ref to `target`. Used to fast-forward `refs/heads/main`
/// to the just-deployed proposal commit. Uses `update-ref`, not
/// `branch -f`, so it works regardless of where HEAD currently sits.
pub async fn git_update_ref(dir: &Path, refname: &str, target: &str) -> Result<()> {
    git(dir, &["update-ref", refname, target]).await
}

/// Write a systemd drop-in for `container@<container>.service` that applies
/// our default resource caps. Goes under `/run/systemd/system/...` so it's
/// ephemeral (regenerated on every spawn / rebuild).
fn set_resource_limits(container: &str) -> Result<()> {
    let dir = format!("/run/systemd/system/container@{container}.service.d");
    std::fs::create_dir_all(&dir).with_context(|| format!("create {dir}"))?;
    let path = format!("{dir}/hyperhive-limits.conf");
    let content =
        format!("[Service]\nMemoryMax={DEFAULT_MEMORY_MAX}\nCPUQuota={DEFAULT_CPU_QUOTA}\n",);
    std::fs::write(&path, content).with_context(|| format!("write {path}"))?;
    tracing::info!(
        %path,
        memory_max = DEFAULT_MEMORY_MAX,
        cpu_quota = DEFAULT_CPU_QUOTA,
        "wrote resource limits drop-in"
    );
    Ok(())
}

async fn systemd_daemon_reload() -> Result<()> {
    let out = Command::new("systemctl")
        .arg("daemon-reload")
        .output()
        .await
        .context("invoke systemctl daemon-reload")?;
    if !out.status.success() {
        bail!(
            "systemctl daemon-reload failed ({}): {}",
            out.status,
            String::from_utf8_lossy(&out.stderr).trim()
        );
    }
    Ok(())
}

/// Idempotently rewrite the lines in `/etc/nixos-containers/<container>.conf`
/// that hive-c0re owns: `PRIVATE_NETWORK` (forced 0 so the agent's web UI port
/// is reachable on the host) and `EXTRA_NSPAWN_FLAGS` (the runtime-dir bind).
/// The start script expands `$EXTRA_NSPAWN_FLAGS` unquoted into the
/// `systemd-nspawn` command.
/// Where in the container's filesystem the manager sees its agents tree.
/// Matches the `/agents` path that pre-Phase-8 hosts declared via
/// `containers.hm1nd.bindMounts."/agents"`.
pub const CONTAINER_MANAGER_AGENTS_MOUNT: &str = "/agents";

/// Where the manager sees the applied trees of every agent, read-only.
/// Manager runs `git fetch /applied/<n>/.git refs/tags/*:refs/tags/applied/*`
/// to learn what hive-c0re deployed (or rejected, or failed to
/// build); the RO bind makes accidental writes impossible from
/// inside the container.
pub const CONTAINER_MANAGER_APPLIED_MOUNT: &str = "/applied";

/// The on-host root that gets bind-mounted to `/agents` inside the manager.
/// Hard-coded to match `AGENT_STATE_ROOT` in coordinator.rs (kept duplicated
/// here so lifecycle stays usable as a leaf module).
const HOST_AGENTS_ROOT: &str = "/var/lib/hyperhive/agents";

/// On-host applied repo root, mirrored RO into the manager. Matches
/// `APPLIED_STATE_ROOT` in coordinator.rs.
const HOST_APPLIED_ROOT: &str = "/var/lib/hyperhive/applied";

/// On-host meta repo root, mirrored RO into the manager. Matches
/// `meta::meta_dir()` but duplicated here so lifecycle stays a leaf.
const HOST_META_ROOT: &str = "/var/lib/hyperhive/meta";

fn set_nspawn_flags(
    container: &str,
    runtime_dir: &Path,
    claude_dir: &Path,
    notes_dir: &Path,
) -> Result<()> {
    let path = format!("/etc/nixos-containers/{container}.conf");
    let original = std::fs::read_to_string(&path).with_context(|| format!("read {path}"))?;
    let mut binds = format!(
        "--bind={runtime}:{CONTAINER_RUNTIME_MOUNT} --bind={claude}:{CONTAINER_CLAUDE_MOUNT} --bind={notes}:{CONTAINER_NOTES_MOUNT}",
        runtime = runtime_dir.display(),
        claude = claude_dir.display(),
        notes = notes_dir.display(),
    );
    if container == MANAGER_NAME {
        use std::fmt::Write as _;
        // systemd-nspawn refuses to start a container whose bind
        // source doesn't exist. The meta repo is created by the
        // startup migration, but make sure the directory is there
        // before the manager comes up in case set_nspawn_flags fires
        // first (e.g. cold start with no agents).
        std::fs::create_dir_all(HOST_META_ROOT)
            .with_context(|| format!("create {HOST_META_ROOT}"))?;
        // Manager edits sub-agent proposed/ repos and its own. RW so it can
        // git-commit. Sub-agents see only their own /run/hive socket and
        // /root/.claude (no /agents or /applied).
        //
        // /applied is a separate RO mount of the hive-c0re-only applied
        // repos so the manager can `git fetch /applied/<n>/.git
        // refs/tags/*:refs/tags/applied/*` to mirror deployed/failed/
        // denied tags into its proposed clones and diff against
        // what's actually deployed. RO bind makes destructive git
        // plumbing inside the container unable to corrupt applied.
        //
        // /meta is a third RO mount exposing the system-wide deploy
        // flake (`git log /meta --oneline` shows every deploy across
        // every agent; `cat /meta/flake.lock` resolves which sha each
        // agent is pinned at right now).
        let _ = write!(
            binds,
            " --bind={HOST_AGENTS_ROOT}:{CONTAINER_MANAGER_AGENTS_MOUNT}",
        );
        let _ = write!(
            binds,
            " --bind-ro={HOST_APPLIED_ROOT}:{CONTAINER_MANAGER_APPLIED_MOUNT}",
        );
        let _ = write!(
            binds,
            " --bind-ro={HOST_META_ROOT}:{mount}",
            mount = crate::meta::CONTAINER_MANAGER_META_MOUNT,
        );
    }
    let bind_flag = format!("EXTRA_NSPAWN_FLAGS=\"{binds}\"");
    let mut lines: Vec<String> = original
        .lines()
        .filter(|line| {
            let trimmed = line.trim_start();
            // Strip any network-namespace knobs nixos-container's create
            // might have populated. The start script adds `--network-veth`
            // whenever HOST_ADDRESS / LOCAL_ADDRESS (or their IPv6 cousins)
            // are non-empty — and veth implies a private netns, hiding our
            // web-UI port from the host. Force host netns.
            !trimmed.starts_with("EXTRA_NSPAWN_FLAGS=")
                && !trimmed.starts_with("PRIVATE_NETWORK=")
                && !trimmed.starts_with("HOST_ADDRESS=")
                && !trimmed.starts_with("LOCAL_ADDRESS=")
                && !trimmed.starts_with("HOST_ADDRESS6=")
                && !trimmed.starts_with("LOCAL_ADDRESS6=")
                && !trimmed.starts_with("HOST_BRIDGE=")
        })
        .map(str::to_owned)
        .collect();
    lines.push("PRIVATE_NETWORK=0".to_owned());
    lines.push("HOST_ADDRESS=".to_owned());
    lines.push("LOCAL_ADDRESS=".to_owned());
    lines.push("HOST_ADDRESS6=".to_owned());
    lines.push("LOCAL_ADDRESS6=".to_owned());
    lines.push("HOST_BRIDGE=".to_owned());
    lines.push(bind_flag);
    let mut content = lines.join("\n");
    content.push('\n');
    std::fs::write(&path, content).with_context(|| format!("write {path}"))?;
    tracing::info!(%path, "set PRIVATE_NETWORK=0 + EXTRA_NSPAWN_FLAGS");
    Ok(())
}

async fn run(args: &[&str]) -> Result<()> {
    let out = Command::new("nixos-container")
        .args(args)
        .output()
        .await
        .with_context(|| format!("invoke nixos-container {}", args.join(" ")))?;
    let stdout = String::from_utf8_lossy(&out.stdout);
    let stderr = String::from_utf8_lossy(&out.stderr);
    if !stdout.trim().is_empty() {
        tracing::info!(target: "nixos-container", "{}", stdout.trim());
    }
    if !stderr.trim().is_empty() {
        tracing::warn!(target: "nixos-container", "{}", stderr.trim());
    }
    if !out.status.success() {
        bail!(
            "nixos-container {} failed ({}): {}",
            args.join(" "),
            out.status,
            stderr.trim()
        );
    }
    Ok(())
}