refactor: split downloader into modules

lib/history.js

@@ -0,0 +1,30 @@
+const fs = require('fs');
+const path = require('path');
+const { HISTORY_FILE, HISTORY_LIMIT } = require('./config');
+
+function loadHistory() {
+  try {
+    if (fs.existsSync(HISTORY_FILE)) return JSON.parse(fs.readFileSync(HISTORY_FILE, 'utf-8'));
+  } catch {}
+  return [];
+}
+
+function saveHistory(history) {
+  fs.mkdirSync(path.dirname(HISTORY_FILE), { recursive: true });
+  fs.writeFileSync(HISTORY_FILE, JSON.stringify(history, null, 2), 'utf-8');
+}
+
+function addHistory(entry) {
+  const history = loadHistory();
+  history.unshift({ ...entry, timestamp: new Date().toISOString() });
+  if (history.length > HISTORY_LIMIT) history.length = HISTORY_LIMIT;
+  saveHistory(history);
+}
+
+function formatTime(isoStr) {
+  const date = new Date(isoStr);
+  const pad = value => String(value).padStart(2, '0');
+  return `${date.getFullYear()}-${pad(date.getMonth() + 1)}-${pad(date.getDate())} ${pad(date.getHours())}:${pad(date.getMinutes())}`;
+}
+
+module.exports = { loadHistory, saveHistory, addHistory, formatTime };