//! Startup auto-migration from the pre-meta layout. Runs before
//! `auto_update::run` and consists of four phases, each idempotent:
//!
//! 1. Per-agent applied repo: rewrite `flake.nix` to the module-only
//!    boilerplate if it isn't already, commit, relocate `deployed/0`
//!    to HEAD so `setup_applied`'s existence check passes.
//! 2. Per-agent proposed repo: ensure the `applied` git remote
//!    points at `/applied/<n>/.git` (re-runs `setup_proposed`'s
//!    `ensure_applied_remote` indirectly via a host-side git call).
//! 3. Meta repo: `meta::sync_agents` over the current agent list —
//!    init the repo on first call, rerender + relock if anything
//!    drifted.
//! 4. Container repoint: for every existing container, run
//!    `nixos-container update <c> --flake meta#<name>` so it
//!    activates against the meta flake. Guarded by a marker file
//!    so the (expensive) phase 4 only runs once across hive-c0re
//!    restarts.
//!
//! Env kill-switch: `HIVE_SKIP_META_MIGRATION=1` skips the whole
//! migration. Use when smoke-testing one agent at a time by hand.

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_NAME};
use crate::meta;

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")
}

const MODULE_FLAKE_MARKER: &str = "nixosModules.default = import ./agent.nix";

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(());
    }
    let names = enumerate_agents().await;
    tracing::info!(count = names.len(), "migration: scanning");

    // 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.hyperhive_flake, coord.dashboard_port, &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 {
        if let Err(e) = repoint_container(name).await {
            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");
    }
    Ok(())
}

async fn enumerate_agents() -> Vec<String> {
    let containers = lifecycle::list().await.unwrap_or_default();
    containers
        .into_iter()
        .filter_map(|c| {
            if c == MANAGER_NAME {
                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=hive-c0re",
            "-c",
            "user.email=hive-c0re@hyperhive",
            "add",
            "flake.nix",
        ],
    )
    .await?;
    raw_git(
        &dir,
        &[
            "-c",
            "user.name=hive-c0re",
            "-c",
            "user.email=hive-c0re@hyperhive",
            "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(())
}

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(())
}