// scanner/scanCartella.js
const path = require('path');
const fsp = require('fs/promises');
const processFile = require('./processFile');
const { sha256 } = require('./utils');
const { SUPPORTED_EXTS } = require('../config');

/**
 * Scansiona ricorsivamente una cartella e ritorna SOLO i cambiamenti
 * (nuovi/modificati) rispetto a previousIndex (mappa { id: meta }).
 */
async function scanCartella(userName, cartella, absCartella, previousIndex) {
  const changes = [];

  async function walk(currentAbs, relPath = '') {
    const entries = await fsp.readdir(currentAbs, { withFileTypes: true });
    for (const e of entries) {
      const absPath = path.join(currentAbs, e.name);
      if (e.isDirectory()) {
        await walk(absPath, path.join(relPath, e.name));
        continue;
      }

      const ext = path.extname(e.name).toLowerCase();
      if (!SUPPORTED_EXTS.has(ext)) continue;

      const fileRelPath = relPath ? `${relPath}/${e.name}` : e.name;
      const id = sha256(`${userName}/${cartella}/${fileRelPath}`);

      const st = await fsp.stat(absPath);
      const prev = previousIndex[id];

      const unchanged =
        prev &&
        prev.size_bytes === st.size &&
        prev.mtimeMs === st.mtimeMs;

      if (unchanged) continue; // NOTE: skip "unchanged"

      const meta = await processFile(
        userName,
        cartella,
        fileRelPath,
        absPath,
        ext,
        st
      );

      meta.id = id; // id sempre presente
      changes.push(meta);
    }
  }

  await walk(absCartella);
  return changes;
}

module.exports = scanCartella;