// Centralised hot-reload watcher.
//
// After the cron rewrites the in-memory data files (search chunks, IMDb
// mappings, IMDb ratings TSV), the existing per-call mtime checks already
// reload them lazily — but the FIRST request post-cron pays a 1-2 s penalty.
//
// This module watches all four data sources and proactively triggers a reload
// in the background as soon as the files change, so users never hit the cold
// path. Debounced because the cron writes ~10 files within seconds.

import { unwatchFile, watch, watchFile } from 'node:fs';
import { IMDB_RATINGS, TMDBINTEGRAL_DIR } from '../config.js';
import { preloadMappings } from './imdbMapping.js';
import { getRatings } from './imdbRatings.js';
import { imdbRatingsCount } from './metrics.js';
import { reloadAllPools } from './searchEngine.js';

const DEBOUNCE_MS = 5000;
const timers = { chunks: null, mappings: null, ratings: null };
const watchers = [];

function debounce(key, fn) {
  clearTimeout(timers[key]);
  timers[key] = setTimeout(() => {
    Promise.resolve(fn()).catch((err) => console.error(`Hot reload (${key}) failed:`, err.message));
  }, DEBOUNCE_MS);
}

async function reloadRatings() {
  // getRatings() checks the file mtime and rebuilds the Map if it changed.
  // Calling it here pre-populates the cache so the next request is hot.
  const map = await getRatings();
  imdbRatingsCount.set(map.size);
  console.log(`Hot reload: imdbratings.tsv (${map.size} entries)`);
}

async function reloadMappings() {
  const out = await preloadMappings();
  console.log(`Hot reload: IMDb mappings (movie=${out.movie}, tv=${out.tv})`);
}

async function reloadChunks() {
  await reloadAllPools();
}

export function startWatchers() {
  // tmdbintegral/ — covers search chunks AND imdb2{movie,tv}.json
  try {
    const w = watch(TMDBINTEGRAL_DIR, (_event, filename) => {
      if (!filename) return;
      if (/^search(movie|tv)\d+\.json$/.test(filename)) {
        debounce('chunks', reloadChunks);
      } else if (filename === 'imdb2movie.json' || filename === 'imdb2tv.json') {
        debounce('mappings', reloadMappings);
      }
    });
    w.unref();
    watchers.push(w);
  } catch (err) {
    console.warn(`Cannot watch ${TMDBINTEGRAL_DIR}:`, err.message);
  }

  // imdbratings.tsv — fs.watch on a single file across a rename(tmp -> file)
  // is unreliable on Linux because the inode changes. fs.watchFile (poll
  // every 10 s) follows the path, not the inode. Cost: one stat() every 10 s.
  watchFile(IMDB_RATINGS, { interval: 10_000 }, (curr, prev) => {
    if (curr.mtimeMs !== prev.mtimeMs) debounce('ratings', reloadRatings);
  });
  watchers.push({ close: () => unwatchFile(IMDB_RATINGS) });
}

export function stopWatchers() {
  for (const w of watchers) {
    try {
      w.close();
    } catch {
      /* ignore */
    }
  }
  watchers.length = 0;
}