//! Single hive-c0re-owned flake at `/var/lib/hyperhive/meta/` that
//! consumes every agent's applied repo as a flake input and exports one
//! `nixosConfiguration` per agent. Containers run against
//! `--flake /var/lib/hyperhive/meta#<name>`; lifecycle ops here drive the
//! lock file so meta's git log is the system-wide deploy audit trail.
//!
//! Flow:
//!   - `sync_agents` (idempotent) — render `flake.nix` for the current
//!     agent set, init the repo on first call, relock if the rendered
//!     contents changed, commit. Used by spawn / destroy / startup
//!     migration.
//!   - `prepare_deploy` + `finalize_deploy` / `abort_deploy` — two-phase
//!     for the `request_apply_commit` path so a failed
//!     `nixos-container update` leaves no orphan commit in meta. Prepare
//!     writes the new lock without committing; finalize commits with the
//!     deploy message; abort `git restore`s the lock back.
//!   - `lock_update_hyperhive` — one-shot for the auto-update path.

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

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

use crate::lifecycle;

const META_ROOT: &str = "/var/lib/hyperhive/meta";
const APPLIED_ROOT: &str = "/var/lib/hyperhive/applied";
const GIT_NAME: &str = "c0re";
const GIT_EMAIL: &str = "c0re@hyperhive";

/// Single-writer lock around every meta-repo operation. Git isn't
/// safe to drive from concurrent processes against the same `.git/`
/// — two simultaneous `git add` / `commit` invocations race on
/// `.git/index.lock`; if either dies before releasing, the lock
/// sticks and the next operation hits "another git process seems to
/// be running" until somebody `rm`s it manually. Holding this mutex
/// across each public function's git+nix calls makes parallel
/// rebuilds (`auto_update` + dashboard-triggered + apply-commit)
/// take turns instead of colliding.
static META_LOCK: Mutex<()> = Mutex::const_new(());

/// Where the manager sees this directory inside its container (RO bind).
#[allow(dead_code)] // wired up by set_nspawn_flags in a follow-up commit
pub const CONTAINER_MANAGER_META_MOUNT: &str = "/meta";

#[derive(Debug, Clone)]
pub struct AgentSpec {
    pub name: String,
    pub is_manager: bool,
    pub port: u16,
}

#[must_use]
pub fn meta_dir() -> PathBuf {
    PathBuf::from(META_ROOT)
}

/// Idempotently reconcile the meta repo with the current agent set.
/// First call inits the git repo, runs `nix flake lock`, and lands a
/// seed commit. Subsequent calls only touch `flake.nix` when the
/// rendered contents differ from disk; an unchanged `flake.nix` is a
/// no-op.
#[allow(dead_code)] // first caller lands in a later commit
pub async fn sync_agents(
    hyperhive_flake: &str,
    dashboard_port: u16,
    operator_pronouns: &str,
    agents: &[AgentSpec],
) -> Result<()> {
    let _guard = META_LOCK.lock().await;
    let dir = meta_dir();
    std::fs::create_dir_all(&dir).with_context(|| format!("create {}", dir.display()))?;

    let new_flake = render_flake(hyperhive_flake, dashboard_port, operator_pronouns, agents);
    let flake_path = dir.join("flake.nix");
    let on_disk = std::fs::read_to_string(&flake_path).unwrap_or_default();
    let initial = !dir.join(".git").exists();

    if !initial && on_disk == new_flake {
        return Ok(());
    }

    std::fs::write(&flake_path, &new_flake)
        .with_context(|| format!("write {}", flake_path.display()))?;

    if initial {
        git(&dir, &["init", "--initial-branch=main"]).await?;
    }
    // Stage flake.nix *before* running nix flake lock. When meta is
    // a git repo, nix treats it as a `git+file://` self-reference;
    // its dirty-tree fetcher includes index entries (tracked +
    // staged) but skips untracked files, so without the stage step
    // an untracked flake.nix surfaces as "source tree does not
    // contain '/flake.nix'". Lock then commit once with both
    // flake.nix and flake.lock — single commit per change.
    git(&dir, &["add", "flake.nix"]).await?;
    nix(&dir, &["flake", "lock"]).await?;
    if std::path::Path::new(&dir).join("flake.lock").exists() {
        git(&dir, &["add", "flake.lock"]).await?;
    }
    let msg = if initial {
        format!("seed meta from {} agent(s)", agents.len())
    } else {
        "regenerate meta flake".to_owned()
    };
    git_commit(&dir, &msg).await?;
    Ok(())
}

/// Phase 1 of an apply-commit deploy. Updates the locked rev of
/// `agent-<name>` to whatever `applied/<name>/main` currently points
/// at and **stages** the lock so `nixos-container update --flake
/// meta#<n>` (which reads via `git+file://`) sees the new rev via
/// the index. Doesn't commit — `finalize_deploy` commits on build
/// success, `abort_deploy` drops the staged change on failure so
/// meta history only carries successful deploys.
#[allow(dead_code)] // wired up by actions::run_apply_commit in a later commit
pub async fn prepare_deploy(name: &str) -> Result<()> {
    let _guard = META_LOCK.lock().await;
    let dir = meta_dir();
    let input = format!("agent-{name}");
    nix(&dir, &["flake", "update", &input]).await?;
    // Stage the new lock — git+file://'s dirty-tree fetcher reads
    // index entries, so the upcoming nixos-container update sees the
    // bumped rev without a commit yet.
    git(&dir, &["add", "flake.lock"]).await
}

/// Phase 2-success. Commit the staged lock with the deployed tag +
/// sha as the message. No-op when the rev was already at the right
/// place (nothing staged → nothing to commit).
#[allow(dead_code)]
pub async fn finalize_deploy(name: &str, sha: &str, tag: &str) -> Result<()> {
    let _guard = META_LOCK.lock().await;
    let dir = meta_dir();
    if !has_staged_changes(&dir).await? {
        return Ok(());
    }
    let short = &sha[..sha.len().min(12)];
    git_commit(&dir, &format!("deploy {name} {tag} {short}")).await
}

/// Phase 2-failure. Unstage + restore the lock so meta returns to
/// the previously-committed shas. The failed proposal is still
/// captured in `applied/<n>`'s annotated `failed/<id>` tag.
#[allow(dead_code)]
pub async fn abort_deploy() -> Result<()> {
    let _guard = META_LOCK.lock().await;
    let dir = meta_dir();
    git(&dir, &["restore", "--staged", "flake.lock"]).await?;
    git(&dir, &["restore", "flake.lock"]).await
}

async fn has_staged_changes(dir: &Path) -> Result<bool> {
    let st = lifecycle::git_command()
        .current_dir(dir)
        .args(["diff", "--cached", "--quiet"])
        .status()
        .await
        .with_context(|| format!("git diff --cached in {}", dir.display()))?;
    // exit 1 = differences present, 0 = no diff, other = error
    match st.code() {
        Some(0) => Ok(false),
        Some(1) => Ok(true),
        _ => bail!("git diff --cached exited unexpectedly"),
    }
}

/// One-shot used by the manual-rebuild path: relock just one
/// agent's input and commit the lock change if any. Single-phase
/// (no separate finalize) because rebuild has no failure-revert
/// semantics — it always wants the latest main.
#[allow(dead_code)] // wired up by lifecycle::rebuild in this commit
pub async fn lock_update_for_rebuild(name: &str) -> Result<()> {
    let _guard = META_LOCK.lock().await;
    let dir = meta_dir();
    let input = format!("agent-{name}");
    nix(&dir, &["flake", "update", &input]).await?;
    if git_is_clean(&dir).await? {
        return Ok(());
    }
    git(&dir, &["add", "flake.lock"]).await?;
    git_commit(&dir, &format!("rebuild {name}: lock update")).await
}

/// Update one or more named inputs in the meta flake and commit
/// the resulting lock change with a single combined message.
/// Used by the dashboard's "update meta inputs" form so the
/// operator can bulk-bump `hyperhive` + selected agents in one
/// shot. Each input name is passed verbatim to
/// `nix flake update`; the caller is responsible for picking
/// real input keys (e.g. via `inputs_view()` snapshotted from
/// the lock file).
#[allow(dead_code)] // wired up by dashboard handler in the same commit
pub async fn lock_update(inputs: &[String]) -> Result<()> {
    if inputs.is_empty() {
        return Ok(());
    }
    let _guard = META_LOCK.lock().await;
    let dir = meta_dir();
    let mut args: Vec<&str> = vec!["flake", "update"];
    for i in inputs {
        args.push(i.as_str());
    }
    nix(&dir, &args).await?;
    if git_is_clean(&dir).await? {
        return Ok(());
    }
    git(&dir, &["add", "flake.lock"]).await?;
    let msg = if inputs.len() == 1 {
        format!("lock update: {}", inputs[0])
    } else {
        format!("lock update: {}", inputs.join(", "))
    };
    git_commit(&dir, &msg).await
}

/// One-shot used by the auto-update path: pin the latest hyperhive
/// rev, commit if the lock changed. Cheaper than `sync_agents`
/// because the per-agent inputs aren't touched.
#[allow(dead_code)]
pub async fn lock_update_hyperhive() -> Result<()> {
    let _guard = META_LOCK.lock().await;
    let dir = meta_dir();
    nix(&dir, &["flake", "update", "hyperhive"]).await?;
    if git_is_clean(&dir).await? {
        return Ok(());
    }
    git(&dir, &["add", "flake.lock"]).await?;
    git_commit(&dir, "bump hyperhive").await
}

fn render_flake(
    hyperhive_flake: &str,
    dashboard_port: u16,
    operator_pronouns: &str,
    agents: &[AgentSpec],
) -> String {
    use std::fmt::Write as _;
    let mut out = String::new();
    out.push_str("{\n  description = \"hyperhive deployed agents\";\n  inputs = {\n");
    let _ = writeln!(out, "    hyperhive.url = \"{hyperhive_flake}\";");
    for spec in agents {
        let _ = writeln!(
            out,
            "    agent-{}.url = \"git+file://{APPLIED_ROOT}/{}\";",
            spec.name, spec.name,
        );
    }
    out.push_str("  };\n  outputs =\n    { self, hyperhive, ... }@inputs:\n    let\n");
    // Free-text operator string — escape backslash + double-quote so a
    // pronouns value like `he/him \ "rare"` round-trips into a valid
    // nix string literal without breaking the flake.
    let pronouns_escaped = operator_pronouns.replace('\\', "\\\\").replace('"', "\\\"");
    let _ = writeln!(
        out,
        "      dashboardPort = {dashboard_port};\n      operatorPronouns = \"{pronouns_escaped}\";\n      mkAgent = {{ name, isManager, port }}:"
    );
    out.push_str(
        r#"        let
          base = if isManager
                 then hyperhive.nixosConfigurations.manager
                 else hyperhive.nixosConfigurations.agent-base;
          input = inputs."agent-${name}";
          service = if isManager then "hive-m1nd" else "hive-ag3nt";
        in
        base.extendModules {
          modules = [
            input.nixosModules.default
            {
              programs.git.config.user = {
                name = name;
                email = "${name}@hyperhive";
              };
              systemd.services.${service}.environment = {
                HIVE_PORT = toString port;
                HIVE_LABEL = name;
                HIVE_DASHBOARD_PORT = toString dashboardPort;
                HIVE_OPERATOR_PRONOUNS = operatorPronouns;
              };
            }
          ];
        };
    in
    {
      nixosConfigurations = {
"#,
    );
    for spec in agents {
        let _ = writeln!(
            out,
            "        {} = mkAgent {{ name = \"{}\"; isManager = {}; port = {}; }};",
            spec.name,
            spec.name,
            if spec.is_manager { "true" } else { "false" },
            spec.port,
        );
    }
    out.push_str("      };\n    };\n}\n");
    out
}

async fn git_is_clean(dir: &Path) -> Result<bool> {
    let out = lifecycle::git_command()
        .current_dir(dir)
        .args(["status", "--porcelain"])
        .output()
        .await
        .with_context(|| format!("git status in {}", dir.display()))?;
    Ok(out.stdout.iter().all(u8::is_ascii_whitespace))
}

async fn 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() {
        bail!(
            "git {} failed ({}): {}",
            args.join(" "),
            out.status,
            String::from_utf8_lossy(&out.stderr).trim()
        );
    }
    Ok(())
}

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
}

async fn nix(dir: &Path, args: &[&str]) -> Result<()> {
    // `--extra-experimental-features` belt-and-suspenders for hosts
    // that haven't set this in nix.conf. The hyperhive module's
    // deploy guide assumes flakes are already enabled, but the cost
    // of being defensive is one extra argv each call.
    let mut all = vec!["--extra-experimental-features", "nix-command flakes"];
    all.extend(args);
    let out = Command::new("nix")
        .current_dir(dir)
        .args(&all)
        .output()
        .await
        .with_context(|| format!("nix {} in {}", args.join(" "), dir.display()))?;
    if !out.status.success() {
        bail!(
            "nix {} failed ({}): {}",
            args.join(" "),
            out.status,
            String::from_utf8_lossy(&out.stderr).trim()
        );
    }
    Ok(())
}