refactor: split downloader into modules

lib/utils.js

@@ -0,0 +1,29 @@
+const fs = require('fs');
+const path = require('path');
+
+function sanitize(name) {
+  return name.replace(/[\/\\:*?"<>|]/g, '_').trim();
+}
+
+function sanitizePathSegment(name, fallback) {
+  const value = sanitize(String(name || '')).replace(/[. ]+$/g, '');
+  return value && value !== '.' && value !== '..' ? value : fallback;
+}
+
+function sleep(ms) {
+  return new Promise(resolve => setTimeout(resolve, ms));
+}
+
+function getDirSize(dirPath) {
+  let size = 0;
+  try {
+    for (const item of fs.readdirSync(dirPath)) {
+      const itemPath = path.join(dirPath, item);
+      const stat = fs.statSync(itemPath);
+      size += stat.isDirectory() ? getDirSize(itemPath) : stat.size;
+    }
+  } catch {}
+  return size;
+}
+
+module.exports = { sanitize, sanitizePathSegment, sleep, getDirSize };