refactor: split downloader into modules

lib/quality.js

@@ -0,0 +1,32 @@
+const { QUALITY_LEVELS, QUALITY_LABELS } = require('./config');
+
+function parseLevel(input) {
+  const value = (input || '').trim().toLowerCase();
+  if (!value) return null;
+  if (/^\d+$/.test(value)) {
+    const index = parseInt(value, 10) - 1;
+    return index >= 0 && index < QUALITY_LEVELS.length ? QUALITY_LEVELS[index] : null;
+  }
+  return QUALITY_LEVELS.includes(value) ? value : null;
+}
+
+function printQualityMenu(currentLevel) {
+  QUALITY_LEVELS.forEach((level, index) => {
+    const mark = level === currentLevel ? '  ←当前' : '';
+    console.log(`    ${index + 1}. ${level.padEnd(10)} ${(QUALITY_LABELS[level] || '').padEnd(8)}${mark}`);
+  });
+}
+
+async function askLevel(ask, currentLevel) {
+  const label = QUALITY_LABELS[currentLevel] ? ` (${QUALITY_LABELS[currentLevel]})` : '';
+  console.log(`\n  当前音质: ${currentLevel}${label}`);
+  console.log('  可选音质:');
+  printQualityMenu(currentLevel);
+  const input = await ask('  选择音质 (输入序号或名称, 回车使用当前): ');
+  const parsed = parseLevel(input);
+  if (parsed) return parsed;
+  if (input.trim()) console.log('  ⚠️  无效选择，使用当前设置');
+  return currentLevel;
+}
+
+module.exports = { parseLevel, printQualityMenu, askLevel };