#!/usr/bin/env node
/**
 * @file systemd-service.js
 * @description Shared helper for installing/removing a systemd `--user`
 * service that keeps the AgentHub dashboard server running across reboots,
 * without needing Claude Code (or any other tool) to be started first.
 * Used by both `agenthub service install` (checkout installs) and
 * `plugin-bootstrap.js` (plugin installs) so the two paths stay in sync.
 * Linux/systemd only — callers fall back to their existing manual-start
 * path when `systemctlAvailable()` is false.
 * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
 */

const fs = require("fs");
const os = require("os");
const path = require("path");
const { spawnSync } = require("child_process");

const MARKER = "# agenthub-managed-unit — regenerated on install, do not edit by hand";

function unitDir() {
  return path.join(os.homedir(), ".config", "systemd", "user");
}

function unitPath(name) {
  return path.join(unitDir(), `${name}.service`);
}

// Test seam: swap the systemctl implementation so unit tests never talk to a
// real service manager. Mirrors tmux.js's __setExecImpl/__reset style.
let execImpl = (args, opts) => spawnSync("systemctl", ["--user", ...args], opts);

function __setExecImpl(fn) {
  execImpl = fn;
}
function __reset() {
  execImpl = (args, opts) => spawnSync("systemctl", ["--user", ...args], opts);
}

function systemctlAvailable() {
  if (process.platform !== "linux") return false;
  return execImpl(["--version"], { stdio: "ignore" }).status === 0;
}

/**
 * Is there a unit by this name, and did WE write it? The distinction decides
 * whether the dashboard may be stopped by hand: a unit of ours means systemd
 * owns the process, and SIGTERM-ing it out of band is the one thing that must
 * never happen (see `restartUserService`).
 */
function unitIsOurs(name) {
  try {
    return fs.readFileSync(unitPath(name), "utf8").includes(MARKER);
  } catch {
    return false;
  }
}

/**
 * `Restart=always`, not `on-failure`: a graceful SIGTERM exits 0, which
 * `on-failure` reads as "meant to stop". One stray kill — or an out-of-band
 * stop during a plugin self-update — then left the dashboard down until some
 * later Claude Code session happened to run the bootstrap. An explicit
 * `systemctl stop` (what uninstall does) still stops it for good.
 */
/**
 * Does our unit still point at `root`? A plugin update moves the install to a
 * new cache directory, and a unit left naming the old one is a failure that
 * shows NOTHING until the next reboot — the dashboard simply does not come
 * back, from a path Claude Code garbage-collected weeks earlier.
 *
 * Pure fs, no `systemctl`: this is called from the bootstrap's fast path, which
 * runs on every single SessionStart and may not spawn a process.
 *
 * A foreign unit is never "stale" — it is not ours to judge or rewrite.
 */
function unitIsStale(name, root) {
  let body;
  try {
    body = fs.readFileSync(unitPath(name), "utf8");
  } catch {
    return false; // no unit at all: nothing to be stale
  }
  if (!body.includes(MARKER)) return false;
  return !body.includes(`\nWorkingDirectory=${root}\n`);
}

/**
 * The directory our unit actually runs from, or null when there is no unit.
 *
 * Deliberately does NOT require the marker: a FOREIGN unit named `agenthub` is
 * not ours to rewrite, but whatever directory it runs from is still a directory
 * nothing here may delete. The one caller is the plugin-cache pruner.
 */
function unitRoot(name) {
  let body;
  try {
    body = fs.readFileSync(unitPath(name), "utf8");
  } catch {
    return null;
  }
  const match = body.match(/^WorkingDirectory=(.*)$/m);
  return match ? match[1].trim() : null;
}

/** Is our unit enabled to start at boot/login — the Settings "start
 *  automatically" switch. Costs a `systemctl` call. */
function unitIsEnabled(name) {
  if (!systemctlAvailable() || !unitIsOurs(name)) return false;
  const res = execImpl(["is-enabled", `${name}.service`], { encoding: "utf8", stdio: "pipe" });
  return String(res.stdout || "").trim() === "enabled";
}

/** Enable or disable our unit for boot — never starts or stops it, so the
 *  server answering the switch stays up either way. */
function setUnitEnabled(name, on) {
  if (!systemctlAvailable()) return "unavailable";
  if (!unitIsOurs(name)) return "foreign";
  return systemctl([on ? "enable" : "disable", `${name}.service`]).status === 0 ? "ok" : "failed";
}

/** Is the unit currently running? Costs a `systemctl` call — never call it
 *  from the fast path. */
function unitIsActive(name) {
  if (!systemctlAvailable()) return false;
  const res = execImpl(["is-active", `${name}.service`], { encoding: "utf8", stdio: "pipe" });
  return String(res.stdout || "").trim() === "active";
}

/** `KillMode=process`: a stop or an update's restart ends the server alone.
 *  tmux forks its server from whichever process first asks for a session —
 *  the dashboard itself, after a boot with autostart on — so it can sit in
 *  this unit's cgroup, and the default `control-group` would kill it and every
 *  lane pane with it. Panes close only on Quit (`server/lib/quit.js`), which
 *  kills them itself. The launchd twin is `AbandonProcessGroup`. */
function unitContent({ description, workingDir, execStart, env }) {
  const envLines = Object.entries(env)
    .map(([k, v]) => `Environment=${k}=${v}`)
    .join("\n");
  return `[Unit]
${MARKER}
Description=${description}
After=network.target

[Service]
Type=simple
WorkingDirectory=${workingDir}
ExecStart=${execStart}
Restart=always
RestartSec=3
KillMode=process
${envLines}

[Install]
WantedBy=default.target
`;
}

function systemctl(args) {
  return execImpl(args, { stdio: "inherit" });
}

/**
 * Writes (or refreshes) the unit file and enables it for boot (unless
 * `enable: false`, which leaves the enabled state as it is) — but starts
 * nothing. Split out of `installUserService` for the plugin self-update, which
 * must be able to point the unit at the new cache directory *before* anything
 * stops the running server, and defer the restart to its very last act.
 *
 * @returns {"written"|"unchanged"|"foreign"|"unavailable"|"failed"}
 */
function writeUserService({ name, description, workingDir, execStart, env = {}, enable = true }) {
  if (!systemctlAvailable()) return "unavailable";
  const body = unitContent({ description, workingDir, execStart, env });
  const target = unitPath(name);
  try {
    if (fs.existsSync(target)) {
      const current = fs.readFileSync(target, "utf8");
      if (!current.includes(MARKER)) return "foreign";
      if (current === body) return "unchanged";
    }
    fs.mkdirSync(unitDir(), { recursive: true });
    fs.writeFileSync(target, body, "utf8");
    systemctl(["daemon-reload"]);
    if (enable) systemctl(["enable", `${name}.service`]);
    return "written";
  } catch {
    return "failed";
  }
}

/**
 * Ask systemd to restart the unit and do NOT wait for it.
 *
 * `--no-block` is the whole point, not a nicety. The caller is the bootstrap
 * spawned by the running server, so it lives in that server's cgroup; the
 * moment systemd stops the old main process, `KillMode=control-group` reaps
 * the caller too. Blocking here means being killed mid-call, which is why the
 * restart must be the last thing the bootstrap does — by then there is nothing
 * left to lose.
 */
function restartUserService(name) {
  if (!systemctlAvailable()) return "unavailable";
  const res = systemctl(["restart", "--no-block", `${name}.service`]);
  return res.status === 0 ? "restarted" : "failed";
}

/**
 * Writes (or refreshes) the unit file and enables + starts it. Idempotent:
 * an unchanged unit is left running as-is; a changed one (e.g. a plugin
 * cache path after an update) is reloaded and restarted.
 *
 * Safe for `agenthub service install`, which is invoked from a user's own
 * shell and is therefore not inside the unit's cgroup. The plugin bootstrap
 * is, and uses `writeUserService` + `restartUserService` instead.
 *
 * @returns {"written"|"unchanged"|"foreign"|"unavailable"|"failed"}
 */
function installUserService(opts) {
  const result = writeUserService(opts);
  if (result === "unchanged") {
    systemctl(["enable", "--now", `${opts.name}.service`]);
  } else if (result === "written") {
    systemctl(["enable", "--now", `${opts.name}.service`]);
    systemctl(["restart", `${opts.name}.service`]);
  }
  return result;
}

/** @returns {"removed"|"absent"|"foreign"|"unavailable"} */
function uninstallUserService(name) {
  if (!systemctlAvailable()) return "unavailable";
  const target = unitPath(name);
  if (!fs.existsSync(target)) return "absent";
  if (!fs.readFileSync(target, "utf8").includes(MARKER)) return "foreign";
  systemctl(["disable", "--now", `${name}.service`]);
  fs.rmSync(target, { force: true });
  systemctl(["daemon-reload"]);
  return "removed";
}

/** Lets the user service start on cold boot, not just after login. Best
 *  effort — some setups require an admin to grant this, so a failure here
 *  is reported, never thrown. */
function enableLinger() {
  const user = os.userInfo().username;
  return spawnSync("loginctl", ["enable-linger", user], { stdio: "ignore" }).status === 0;
}

module.exports = {
  kind: "systemd",
  label: "systemd --user service",
  systemctlAvailable,
  unitIsOurs,
  unitIsStale,
  unitRoot,
  unitIsActive,
  unitIsEnabled,
  setUnitEnabled,
  writeUserService,
  restartUserService,
  installUserService,
  uninstallUserService,
  enableLinger,
  unitPath,
  __setExecImpl,
  __reset,
};