//! First-spawn provisioning: seed the hive-c0re-owned applied repo, and
//! ensure the per-agent state / claude-credentials dirs (btrfs subvolume when
//! available) exist.
//!
//! Seeding is the only write the repo gets from here. Later config changes
//! arrive as forge PRs authored in a clone - nothing edits a working tree in
//! place.

use std::path::Path;

use anyhow::{Context, Result, bail};

use super::git::{git, git_commit, git_rev_parse, git_tag};

/// Seed an agent's applied repo on first spawn, preferring the config the
/// forge already has. `agent-configs/<name>` is authored by whoever created
/// the agent (at swarm level the controller, which writes the config before
/// any hive is told to deploy it), so this takes the forge's `main` when
/// there is one and writes a template only when there is not. Two authors for
/// one file is the failure mode being avoided: whichever wrote second would
/// win, and neither knows about the other.
///
/// The template ([`seed_template`]) is the fallback when there is genuinely
/// nothing to take yet: `swarm-controller` creates `agent-configs/<name>`
/// before telling a hive to deploy, but hasn't necessarily pushed `main` to
/// it, or the forge is unreachable, or this hive has no forge read token.
///
/// Seeding is the only write hive-c0re makes here. Later config changes
/// arrive as forge PRs and are fetched from the forge's `main` (see
/// `actions::advance_applied_to_rev`). `flake.nix` is tracked in the seed
/// and rides along on every fetch.
///
/// A repo that is already there is only checked for its shape (a rebuild
/// finds it already seeded): a missing `deployed/0` tag means it predates the
/// meta-flake layout and is an error.
pub async fn setup_applied(applied_dir: &Path, name: &str) -> Result<()> {
    std::fs::create_dir_all(applied_dir)
        .with_context(|| format!("create {}", applied_dir.display()))?;

    if !applied_dir.join(".git").exists() {
        if crate::forge::fetch_config_main_into_applied(name).await {
            return Ok(());
        }
        seed_template(applied_dir, name).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(())
}

/// Author the initial config in place: `agent.nix` (the agent's own module)
/// 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). `flake.nix`
/// isn't meant to be edited, but it's tracked so it can be read.
///
/// The fallback half of [`setup_applied`]: reached only when the forge has
/// no config for this agent to take.
async fn seed_template(dir: &Path, name: &str) -> Result<()> {
    let agent_path = 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 = dir.join("flake.nix");
    if !flake_path.exists() {
        std::fs::write(&flake_path, initial_flake_nix())
            .with_context(|| format!("write {}", flake_path.display()))?;
    }
    git(dir, &["init", "--initial-branch=main"]).await?;
    git(dir, &["add", "agent.nix", "flake.nix"]).await?;
    git_commit(dir, "hive-c0re init").await
}

/// Create the per-agent Claude credentials dir if missing. Mode 0755 — hive-core
/// needs read+execute to list the directory so `claude_has_session` can detect a
/// valid session; credential files inside (`.credentials.json` etc.) are 0600 so
/// secrets stay private regardless of the directory mode. Idempotent: existing
/// dirs are left untouched (an agent's OAuth tokens survive `destroy`/recreate).
pub fn ensure_claude_dir(claude_dir: &Path) -> Result<()> {
    use std::io;
    if !claude_dir.exists() {
        std::fs::create_dir_all(claude_dir)
            .with_context(|| format!("create {}", claude_dir.display()))?;
    }
    // 0755: hive-core (different user from the agent) needs read+execute to
    // list the directory so `claude_has_session` can detect a valid session.
    // The credential files inside (`.credentials.json` etc.) are 0600 so the
    // secrets themselves stay private regardless of the directory mode.
    //
    // Best-effort: on the first container boot, `hive-agent-user-migrate`
    // chowns this dir to the agent user. After that, hive-core (a different
    // user) cannot chmod it (EPERM) — that's fine because the mode set during
    // initial creation (0755) is preserved through the chown.  Any other error
    // (ENOENT, I/O error) is unexpected and propagated.
    #[cfg(unix)]
    {
        use std::os::unix::fs::PermissionsExt;
        match std::fs::set_permissions(claude_dir, std::fs::Permissions::from_mode(0o755)) {
            Ok(()) => {}
            Err(e) if e.kind() == io::ErrorKind::PermissionDenied => {
                tracing::debug!(
                    path = %claude_dir.display(),
                    "ensure_claude_dir: chmod 755 skipped (dir likely owned by agent user after migration)"
                );
            }
            Err(e) => {
                return Err(e).with_context(|| format!("chmod 755 {}", claude_dir.display()));
            }
        }
    }
    Ok(())
}

/// Create the per-agent state dir if missing. Also creates the sibling
/// `harness/` dir so the first harness startup can write its sqlite files
/// immediately, and the sibling `work/` dir.
pub 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()))?;
    }
    // Harness and work dirs are siblings of the agent-visible state dir.
    if let Some(parent) = notes_dir.parent() {
        for sibling in ["harness", crate::paths::WORK_SUBDIR] {
            let dir = parent.join(sibling);
            if !dir.exists() {
                std::fs::create_dir_all(&dir)
                    .with_context(|| format!("create {}", dir.display()))?;
            }
        }
    }
    Ok(())
}

/// Ensure agent `name`'s persistent state root
/// (`/var/lib/hyperhive/agents/<name>`) is a btrfs subvolume — when the host
/// filesystem supports it — BEFORE the per-agent subdirs (`state/`, `claude/`,
/// `harness/`, `work/`) are created by `ensure_state_dir` / `ensure_claude_dir`.
///
/// Progressive enhancement: if the root already exists
/// (any agent provisioned before this landed, plain dir or subvol) it's left
/// exactly as-is — no auto-migration — and the priv round-trip is skipped. On
/// a non-btrfs host the priv op no-ops and the root is later created as a
/// plain dir by `ensure_*_dir`, identical to the old behaviour. Only a
/// brand-new agent on a btrfs host gets a real subvolume. Subvolume creation
/// is privileged, so it's delegated to hive-priv.
pub async fn ensure_agent_state_subvolume(name: &str) -> Result<()> {
    let agent = hive_types::Ident::parse(name)
        .map_err(|e| anyhow::anyhow!("invalid agent name {name:?}: {e}"))?;
    let root = crate::paths::agent_state_dir(&agent);
    if root.exists() {
        return Ok(());
    }
    crate::priv_client::ensure_agent_subvolume(name)
        .await
        .with_context(|| format!("ensure btrfs subvolume for agent {name}"))
}

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
/// swarm's `internal/meta` flake as a flake input. The wrapper is
/// intentionally permissive:
///
/// - Manager edits `inputs.* = …` to add other flakes (e.g. an MCP
///   server's own flake) — the lock for those lands in the agent's
///   own `flake.lock` and rolls up into meta's lock transitively.
/// - The outputs block forwards every input (minus `self`) into
///   `agent.nix` as the `flakeInputs` module argument, so the
///   manager just references `flakeInputs.<name>.packages.${pkgs.system}.default`
///   without further plumbing.
///
/// Identity injection (`HIVE_PORT` / `HIVE_LABEL` / dashboard port /
/// git committer) still lives in the meta flake's wrapper.
pub fn initial_flake_nix() -> &'static str {
    "{\n  description = \"hyperhive agent\";\n  inputs = { };\n  outputs =\n    { self, ... }@inputs:\n    {\n      nixosModules.default = {\n        imports = [ ./agent.nix ];\n        _module.args.flakeInputs = builtins.removeAttrs inputs [ \"self\" ];\n      };\n    };\n}\n"
}