// backend/metrics.js (ESM)
// Mount with: import registerMetrics from './metrics.js'; registerMetrics(app, { query: sql });

export default function registerMetrics(app, db) {
  if (!app || !db || typeof db.query !== 'function') {
    throw new Error('metrics: app and a {query(sql, [params])} db are required');
  }

  let cache = { at: 0, data: null };
  const CACHE_MS = 5_000; // front-end polls at 10–60 min; 5s is fine here

  app.get('/api/metrics', async (_req, res) => {
    try {
      const now = Date.now();
      if (cache.data && (now - cache.at) < CACHE_MS) {
        res.setHeader('Cache-Control', 'no-store');
        return res.json(cache.data);
      }

      // Users = distinct payer addresses who have at least one successful upload (cid not null)
      const u = await db.query(`
        SELECT COUNT(DISTINCT lower(address))::bigint AS users
        FROM public.payments
        WHERE address IS NOT NULL AND address <> '' AND cid IS NOT NULL
      `);

      // Uploads + total bytes = only rows with a CID
      const p = await db.query(`
        SELECT
          COUNT(*)::bigint                         AS uploads,
          COALESCE(SUM(size_bytes), 0)::bigint     AS bytes
        FROM public.payments
        WHERE cid IS NOT NULL
      `);

      const payload = {
        users:   Number(u.rows?.[0]?.users  ?? 0),
        uploads: Number(p.rows?.[0]?.uploads?? 0),
        bytes:   Number(p.rows?.[0]?.bytes  ?? 0),
      };

      cache = { at: now, data: payload };
      res.setHeader('Cache-Control', 'no-store');
      res.json(payload);
    } catch (err) {
      console.error('metrics route error:', err);
      res.status(500).json({ ok:false, error:'metrics_failed' });
    }
  });
}