// Lists and extracts files inside archives. ZIP/7Z/RAR go through 7-Zip (WASM,
// in a worker thread); TAR and .tar.gz go through node-tar. Extracted entries
// are cached under EXTRACT_DIR/<file id>/ and can always be re-extracted.

const fs = require('fs');
const path = require('path');
const { Worker } = require('worker_threads');
const tar = require('tar');

const EXTRACT_DIR = path.resolve(process.env.EXTRACT_DIR || './extracted');
const TAR_FILE_TYPES = ['File', 'OldFile', 'ContiguousFile'];

let worker = null;
let nextId = 1;
const pending = new Map();

function failPending(err) {
  for (const p of pending.values()) p.reject(err);
  pending.clear();
  worker = null;
}

// The worker keeps the process alive only while a request is outstanding, so
// an idle worker never stops Node from exiting.
function sevenZip(message) {
  if (!worker) {
    worker = new Worker(path.join(__dirname, 'archiveWorker.js'));
    worker.on('message', ({ id, result, error }) => {
      const p = pending.get(id);
      pending.delete(id);
      if (pending.size === 0 && worker) worker.unref();
      if (p) error ? p.reject(new Error(error)) : p.resolve(result);
    });
    worker.on('error', failPending);
    worker.on('exit', () => failPending(new Error('Archive worker stopped')));
  }
  return new Promise((resolve, reject) => {
    const id = nextId++;
    pending.set(id, { resolve, reject });
    worker.ref();
    worker.postMessage({ id, ...message });
  });
}

const isTar = (format) => format === 'tar' || format === 'tgz';
const clean = (p) => p.replace(/^\.\//, '');

// Clutter archivers add (macOS resource forks, Finder/Explorer files).
function isJunk(entryPath) {
  const parts = clean(entryPath).split('/');
  const name = parts[parts.length - 1];
  return parts.includes('__MACOSX') || name.startsWith('._') || name === '.DS_Store' || name === 'Thumbs.db';
}

// Paths that could land outside the extraction folder are never used.
function isSafe(entryPath) {
  return Boolean(entryPath) && !path.isAbsolute(entryPath) && !entryPath.split(/[\\/]/).includes('..');
}

// file: { file_path, format }. Returns [{ path, size }] of real files.
async function listEntries(file) {
  const abs = path.resolve(file.file_path);
  let raw;
  if (isTar(file.format)) {
    raw = [];
    await tar.t({
      file: abs,
      onReadEntry: (e) => { if (TAR_FILE_TYPES.includes(e.type)) raw.push({ path: e.path, size: e.size }); },
    });
  } else {
    raw = await sevenZip({ op: 'list', archive: abs });
  }
  return raw.filter((e) => isSafe(e.path) && !isJunk(e.path));
}

function tempDir() {
  fs.mkdirSync(EXTRACT_DIR, { recursive: true });
  return fs.mkdtempSync(path.join(EXTRACT_DIR, '.tmp-'));
}

// Extracts entries into destDir. Returns Map(entry path -> absolute path) for
// the ones that came out; archive-level failures throw.
async function extractMany(file, entryPaths, destDir) {
  const abs = path.resolve(file.file_path);
  const wanted = new Set(entryPaths.filter(isSafe));
  if (isTar(file.format)) {
    await tar.x({ file: abs, cwd: destDir, filter: (p) => wanted.has(p) });
  } else {
    const { code, error } = await sevenZip({ op: 'extract', archive: abs, entries: [...wanted], destDir });
    if (code !== 0 && error) console.warn(`7-Zip reported a problem extracting from ${abs}: ${error}`);
  }
  const out = new Map();
  for (const p of wanted) {
    const target = path.resolve(destDir, p);
    if (target.startsWith(destDir + path.sep) && fs.existsSync(target)) out.set(p, target);
  }
  return out;
}

function entryCachePath(fileId, entry) {
  return path.join(EXTRACT_DIR, String(fileId), `${entry.id}${path.extname(entry.path).toLowerCase()}`);
}

const inflight = new Map();

// file: { id, file_path, format }; entry: { id, path }. Returns the absolute
// path of a cached copy, extracting it on first use.
async function extractEntry(file, entry) {
  const dest = entryCachePath(file.id, entry);
  if (fs.existsSync(dest)) return dest;
  if (!inflight.has(dest)) {
    const job = (async () => {
      fs.mkdirSync(path.dirname(dest), { recursive: true });
      const tmp = tempDir();
      try {
        const got = (await extractMany(file, [entry.path], tmp)).get(entry.path);
        if (!got) throw new Error(`Could not extract ${clean(entry.path)} from the archive`);
        fs.renameSync(got, dest);
      } finally {
        fs.rmSync(tmp, { recursive: true, force: true });
      }
    })().finally(() => inflight.delete(dest));
    inflight.set(dest, job);
  }
  await inflight.get(dest);
  return dest;
}

function removeExtracted(fileId) {
  fs.rmSync(path.join(EXTRACT_DIR, String(fileId)), { recursive: true, force: true });
}

module.exports = { listEntries, extractMany, extractEntry, removeExtracted, tempDir, isJunk };