/**
 * @file Scheduled database backups (Settings → Data → Backup). Once a day, at
 * a chosen local hour of the server, the dashboard's SQLite database is copied
 * into a folder the admin picked: `VACUUM INTO` on a READ-ONLY connection in a
 * worker thread — a consistent snapshot that writes from other connections
 * never restart, compacted (1.25 GB → ~0.7 GB), while the event loop keeps
 * serving (≈30 s at that size). The file name is server-made,
 * `agenthub-YYYYMMDD-HHMMSS.db`, written as `<name>.partial` and renamed once
 * complete. Rotation deletes ONLY regular files matching that exact name, oldest
 * first beyond `keep` — nothing else in the folder, never through a symlink.
 * Settings live in the settings file: AGENTHUB_BACKUP_DIR (empty = off),
 * AGENTHUB_BACKUP_HOUR (0–23, default 2), AGENTHUB_BACKUP_KEEP (1–365, default
 * 7). A missed day (server down at the hour) runs at the next start; a failed
 * one is retried the next day or by "Back up now", never every minute. The
 * scheduler ticks every DASHBOARD_BACKUP_TICK_MS (default 60 s, 0 = off).
 * Restoring is manual: stop AgentHub, copy a backup over the database, start.
 * This file is also the worker's entry point.
 * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
 */

"use strict";

const fs = require("node:fs");
const os = require("node:os");
const path = require("node:path");
const { Worker, isMainThread, workerData, parentPort } = require("node:worker_threads");

const KEYS = {
  dir: "AGENTHUB_BACKUP_DIR",
  hour: "AGENTHUB_BACKUP_HOUR",
  keep: "AGENTHUB_BACKUP_KEEP",
};
const NAME_RE = /^agenthub-(\d{8})-(\d{6})\.db$/;

const coded = (message, code) => Object.assign(new Error(message), { code });

function int(value, lo, hi, fallback) {
  const n = Number(value);
  return value !== undefined && value !== "" && Number.isInteger(n) && n >= lo && n <= hi
    ? n
    : fallback;
}

function backupConfig(env = process.env) {
  return {
    dir: env[KEYS.dir] || "",
    hour: int(env[KEYS.hour], 0, 23, 2),
    keep: int(env[KEYS.keep], 1, 365, 7),
  };
}

/** Absolute, existing, writable directory → its resolved path; else INVALID_PATH. */
function validateBackupDir(input) {
  const invalid = (message) => coded(message, "INVALID_PATH");
  const trimmed = String(input).trim();
  if (/[\x00-\x1f]/.test(trimmed)) throw invalid("the folder may not contain control characters");
  const expanded = trimmed.replace(/^~(?=$|\/)/, os.homedir());
  if (!path.isAbsolute(expanded)) throw invalid("the backup folder must be an absolute path");
  const resolved = path.resolve(expanded);
  let st;
  try {
    st = fs.statSync(resolved);
  } catch {
    throw invalid(`Directory does not exist: ${resolved}`);
  }
  if (!st.isDirectory()) throw invalid(`Not a directory: ${resolved}`);
  try {
    fs.accessSync(resolved, fs.constants.W_OK);
  } catch {
    throw invalid(`AgentHub cannot write to ${resolved}`);
  }
  return resolved;
}

/** Local `YYYYMMDD-HHMMSS`. */
function stamp(d) {
  const p = (n) => String(n).padStart(2, "0");
  return (
    `${d.getFullYear()}${p(d.getMonth() + 1)}${p(d.getDate())}-` +
    `${p(d.getHours())}${p(d.getMinutes())}${p(d.getSeconds())}`
  );
}

/** AgentHub's own backups in `dir`, newest first. Symlinks and look-alikes are not ours. */
function listBackups(dir) {
  return fs
    .readdirSync(dir, { withFileTypes: true })
    .filter((e) => e.isFile() && NAME_RE.test(e.name))
    .map((e) => {
      const st = fs.statSync(path.join(dir, e.name));
      return { name: e.name, size: st.size, mtime: st.mtime.toISOString() };
    })
    .sort((a, b) => (a.name < b.name ? 1 : -1));
}

/** Delete our backups beyond the newest `keep`; returns the names removed. */
function rotate(dir, keep) {
  const old = listBackups(dir).slice(keep);
  for (const f of old) fs.unlinkSync(path.join(dir, f.name));
  return old.map((f) => f.name);
}

/** Whether the scheduler should back up now. `attemptedDay` = YYYYMMDD already tried. */
function dueNow(now, cfg, files, attemptedDay) {
  if (!cfg.dir || now.getHours() < cfg.hour) return false;
  const today = stamp(now).slice(0, 8);
  if (attemptedDay === today) return false;
  return !files.some((f) => NAME_RE.exec(f.name)?.[1] === today);
}

function vacuumInto(dbPath, out) {
  return new Promise((resolve, reject) => {
    const w = new Worker(__filename, { workerData: { agenthubBackupWorker: true, dbPath, out } });
    w.once("message", (m) => (m.error ? reject(coded(m.error.message, m.error.code)) : resolve()));
    w.once("error", reject);
    w.once(
      "exit",
      (code) => code !== 0 && reject(coded(`backup worker exited (${code})`, "EBACKUP"))
    );
  });
}

let running = null;
let last = null;

function runBackup() {
  if (running) return running;
  running = (async () => {
    const { dir: configured, keep } = backupConfig();
    if (!configured) throw coded("no backup folder is set", "ENOBACKUPDIR");
    const started = new Date();
    let partial = null;
    try {
      const dir = validateBackupDir(configured); // it may have been unmounted since
      const name = `agenthub-${stamp(started)}.db`;
      partial = path.join(dir, `${name}.partial`);
      await vacuumInto(require("../db").DB_PATH, partial);
      fs.renameSync(partial, path.join(dir, name));
      partial = null;
      const removed = rotate(dir, keep);
      const size = fs.statSync(path.join(dir, name)).size;
      last = {
        at: started.toISOString(),
        ok: true,
        file: name,
        size,
        ms: Date.now() - started,
        removed,
      };
      return last;
    } catch (err) {
      if (partial) fs.rmSync(partial, { force: true });
      last = { at: started.toISOString(), ok: false, error: err.message };
      throw err;
    }
  })().finally(() => {
    running = null;
  });
  return running;
}

const isRunning = () => running !== null;
const lastResult = () => last;

function startBackupScheduler() {
  const every = Number(process.env.DASHBOARD_BACKUP_TICK_MS ?? 60_000);
  if (!Number.isFinite(every) || every <= 0) return;
  let attemptedDay = null;
  const t = setInterval(() => {
    const cfg = backupConfig();
    if (!cfg.dir || running) return;
    const now = new Date();
    let files = [];
    try {
      files = listBackups(cfg.dir);
    } catch {
      /* folder gone: runBackup reports it */
    }
    if (!dueNow(now, cfg, files, attemptedDay)) return;
    attemptedDay = stamp(now).slice(0, 8);
    runBackup().then(
      (r) => console.log(`[backup] ${r.file} (${(r.size / 1048576).toFixed(0)} MB, ${r.ms} ms)`),
      (err) => console.warn(`[backup] failed: ${err.message}`)
    );
  }, every);
  if (t.unref) t.unref();
}

if (!isMainThread && workerData?.agenthubBackupWorker) {
  // Same driver order as server/db.js: better-sqlite3, else node:sqlite.
  let conn;
  try {
    try {
      const Database = require("better-sqlite3");
      conn = new Database(workerData.dbPath, { readonly: true });
    } catch {
      const Database = require("../compat-sqlite");
      conn = new Database(workerData.dbPath, { readonly: true });
    }
    conn.pragma("busy_timeout = 5000");
    conn.prepare("VACUUM INTO ?").run(workerData.out);
    parentPort.postMessage({ ok: true });
  } catch (err) {
    parentPort.postMessage({ error: { message: err.message, code: err.code || "EBACKUP" } });
  } finally {
    conn?.close();
  }
}

module.exports = {
  KEYS,
  backupConfig,
  validateBackupDir,
  listBackups,
  rotate,
  dueNow,
  runBackup,
  isRunning,
  lastResult,
  startBackupScheduler,
};