feat: romaji index for Japanese kanji song search

Backend:
- Add /api/romaji-index endpoint using kuromoji morphological analyzer
- Fetches all Navidrome songs, converts kanji → hiragana readings → romaji
- Only indexes songs with Japanese characters; caches for 20 min
- /api/romaji-index DELETE clears cache (force rebuild)

Frontend:
- fetchRomajiIndex() in api.js: lazy-fetches and caches the index
- doLocalSearch: when query is romaji (ASCII), queries romaji index in
  parallel with Navidrome search3 and merges+deduplicates results

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/novasonic-server.js

@@ -10,6 +10,7 @@
 
 const express      = require('express');
 const { execSync } = require('child_process');
+const { createHash } = require('crypto');
 const path         = require('path');
 const fs           = require('fs');
 const https        = require('https');
@@ -19,6 +20,139 @@ const { jobs, updateJob, log } = require('./lib/jobs');
 const { lookupItunesTrackMeta, fetchItunesTracks, searchItunesAlbumTracks } = require('./lib/metadata');
 const { downloadTrack, downloadAlbumTracks } = require('./lib/downloader');
 
+// ─── ROMAJI INDEX ─────────────────────────────────────────────────────────────
+// Converts kanji/kana → romaji so users can search Japanese songs phonetically.
+
+let _tokenizer = null;
+try {
+  const kuromoji = require('kuromoji');
+  kuromoji.builder({ dicPath: path.join(require.resolve('kuromoji'), '../../dict') })
+    .build((err, t) => {
+      if (err) console.warn('⚠️  kuromoji failed to load:', err.message);
+      else     { _tokenizer = t; console.log('✅ kuromoji tokenizer ready'); }
+    });
+} catch { console.warn('⚠️  kuromoji not installed — run: cd backend && npm install'); }
+
+// katakana→hiragana shift (kuromoji readings come back in katakana)
+function _kataToHira(s) { return s.replace(/[ァ-ヶ]/g, c => String.fromCharCode(c.charCodeAt(0) - 0x60)); }
+
+// Full hiragana → romaji table (includes digraphs + っ doubling)
+const _H2R = {
+  'あ':'a','い':'i','う':'u','え':'e','お':'o',
+  'か':'ka','き':'ki','く':'ku','け':'ke','こ':'ko',
+  'さ':'sa','し':'shi','す':'su','せ':'se','そ':'so',
+  'た':'ta','ち':'chi','つ':'tsu','て':'te','と':'to',
+  'な':'na','に':'ni','ぬ':'nu','ね':'ne','の':'no',
+  'は':'ha','ひ':'hi','ふ':'fu','へ':'he','ほ':'ho',
+  'ま':'ma','み':'mi','む':'mu','め':'me','も':'mo',
+  'や':'ya','ゆ':'yu','よ':'yo',
+  'ら':'ra','り':'ri','る':'ru','れ':'re','ろ':'ro',
+  'わ':'wa','を':'wo','ん':'n',
+  'が':'ga','ぎ':'gi','ぐ':'gu','げ':'ge','ご':'go',
+  'ざ':'za','じ':'ji','ず':'zu','ぜ':'ze','ぞ':'zo',
+  'だ':'da','ぢ':'di','づ':'du','で':'de','ど':'do',
+  'ば':'ba','び':'bi','ぶ':'bu','べ':'be','ぼ':'bo',
+  'ぱ':'pa','ぴ':'pi','ぷ':'pu','ぺ':'pe','ぽ':'po',
+  'きゃ':'kya','きゅ':'kyu','きょ':'kyo',
+  'しゃ':'sha','しゅ':'shu','しょ':'sho',
+  'ちゃ':'cha','ちゅ':'chu','ちょ':'cho',
+  'にゃ':'nya','にゅ':'nyu','にょ':'nyo',
+  'ひゃ':'hya','ひゅ':'hyu','ひょ':'hyo',
+  'みゃ':'mya','みゅ':'myu','みょ':'myo',
+  'りゃ':'rya','りゅ':'ryu','りょ':'ryo',
+  'ぎゃ':'gya','ぎゅ':'gyu','ぎょ':'gyo',
+  'じゃ':'ja','じゅ':'ju','じょ':'jo',
+  'びゃ':'bya','びゅ':'byu','びょ':'byo',
+  'ぴゃ':'pya','ぴゅ':'pyu','ぴょ':'pyo',
+  'ふぁ':'fa','ふぃ':'fi','ふぇ':'fe','ふぉ':'fo',
+  'てぃ':'ti','でぃ':'di','とぅ':'tu','どぅ':'du',
+  'ゐ':'i','ゑ':'e','ヴ':'vu',
+};
+function _hiraToRomaji(str) {
+  let out = '', i = 0;
+  while (i < str.length) {
+    if (str[i] === 'っ') {
+      const nxt = _H2R[str.slice(i+1,i+3)] || _H2R[str[i+1]] || '';
+      out += nxt[0] || ''; i++; continue;
+    }
+    const two = _H2R[str.slice(i,i+2)];
+    if (two) { out += two; i += 2; continue; }
+    out += _H2R[str[i]] ?? str[i]; i++;
+  }
+  return out;
+}
+
+const JP_RE = /[぀-ヿ㐀-䶿一-鿿＀-￯]/;
+function _toRomaji(text) {
+  if (!text || !_tokenizer || !JP_RE.test(text)) return text || '';
+  const tokens = _tokenizer.tokenize(text);
+  const hira = tokens.map(t => {
+    const r = t.reading;
+    return (r && r !== '*') ? _kataToHira(r) : t.surface_form;
+  }).join('');
+  return _hiraToRomaji(hira).toLowerCase();
+}
+
+// Cache: key = "ndUrl|user" → { ts, index }
+const _romajiCache = new Map();
+const ROMAJI_TTL   = 20 * 60 * 1000; // 20 min
+
+async function _fetchNdSongs(ndUrl, user, pass) {
+  const salt  = Math.random().toString(36).slice(2, 10);
+  const token = createHash('md5').update(pass + salt).digest('hex');
+  const base  = `${ndUrl}/rest/search3.view?u=${encodeURIComponent(user)}&t=${token}&s=${salt}&v=1.16.1&c=novasonic&f=json&albumCount=0&artistCount=0`;
+  const songs = [];
+  let offset = 0;
+  while (true) {
+    const r    = await fetch(`${base}&query=&songCount=500&songOffset=${offset}`).then(r => r.json());
+    const page = r['subsonic-response']?.searchResult3?.song || [];
+    songs.push(...page);
+    if (page.length < 500) break;
+    offset += 500;
+  }
+  return songs;
+}
+
+// GET /api/romaji-index?ndUrl=...&user=...&pass=...
+app.get('/api/romaji-index', async (req, res) => {
+  const { ndUrl, user, pass } = req.query;
+  if (!ndUrl || !user || !pass) return res.status(400).json({ error: 'missing params' });
+  if (!_tokenizer) return res.status(503).json({ error: 'tokenizer not ready — try again in a few seconds' });
+
+  const key    = `${ndUrl}|${user}`;
+  const cached = _romajiCache.get(key);
+  if (cached && Date.now() - cached.ts < ROMAJI_TTL) return res.json(cached.index);
+
+  try {
+    const songs = await _fetchNdSongs(ndUrl, user, pass);
+    const index = songs
+      .filter(s => JP_RE.test(s.title) || JP_RE.test(s.artist) || JP_RE.test(s.album))
+      .map(s => ({
+        id:       s.id,
+        r:        [_toRomaji(s.title), _toRomaji(s.artist), _toRomaji(s.album)].join(' '),
+        title:    s.title,
+        artist:   s.artist    || '',
+        album:    s.album     || '',
+        coverArt: s.coverArt  || '',
+        duration: s.duration  || 0,
+        albumId:  s.albumId   || '',
+        artistId: s.artistId  || '',
+      }));
+    _romajiCache.set(key, { ts: Date.now(), index });
+    console.log(`✅ Romaji index built: ${index.length} JP songs (${songs.length} total)`);
+    res.json(index);
+  } catch (e) {
+    console.error('Romaji index error:', e);
+    res.status(500).json({ error: e.message });
+  }
+});
+
+// DELETE /api/romaji-index — force rebuild on next request
+app.delete('/api/romaji-index', (req, res) => {
+  _romajiCache.clear();
+  res.json({ ok: true });
+});
+
 // ─── INIT ─────────────────────────────────────────────────────────────────────
 const app = express();
 app.use((req, res, next) => {

backend/package.json

@@ -0,0 +1,7 @@
+{
+  "name": "novasonic-backend",
+  "private": true,
+  "dependencies": {
+    "kuromoji": "^0.1.2"
+  }
+}

src/api.js

@@ -39,6 +39,25 @@ export async function ndAuth() {
   return S._ndToken;
 }
 
+// ─── ROMAJI INDEX ───
+// Fetched once per session from the backend, cached in memory.
+let _romajiIndex = null;
+let _romajiIndexFetch = null; // in-flight promise dedup
+
+export async function fetchRomajiIndex() {
+  if (!S.cfg.backendUrl || !S.cfg.url || !S.cfg.user || !S.cfg.pass) return null;
+  if (_romajiIndex) return _romajiIndex;
+  if (_romajiIndexFetch) return _romajiIndexFetch;
+  _romajiIndexFetch = fetch(
+    `${S.cfg.backendUrl}/api/romaji-index?ndUrl=${encodeURIComponent(S.cfg.url)}&user=${encodeURIComponent(S.cfg.user)}&pass=${encodeURIComponent(S.cfg.pass)}`
+  ).then(r => r.ok ? r.json() : null)
+   .then(idx => { _romajiIndex = idx; _romajiIndexFetch = null; return idx; })
+   .catch(() => { _romajiIndexFetch = null; return null; });
+  return _romajiIndexFetch;
+}
+
+export function invalidateRomajiIndex() { _romajiIndex = null; }
+
 // ─── ITUNES ───
 // Route through backend proxy to avoid CORS; fall back to direct if no backend configured.
 function _itunesBase() {

src/views.js

@@ -6,6 +6,7 @@ import { playQueue, dlSongLocal, playPreview } from './player.js';
 import { showCtxMenu, openEditPlModal, openDlModal, closeSidebar, switchNavMode } from './ui.js';
 import { closeNowPlaying, closeNpMenu } from './nowplaying.js';
 import { makeCard, makeAlbumCard, makeSongItem, makeGlobalTrackItem, mkSection } from './components.js';
+import { fetchRomajiIndex } from './api.js';
 import { loadSpotifyImporter } from './spotify.js';
 
 // ─── NAVIGATION HISTORY ───
@@ -723,16 +724,25 @@ export async function doLocalSearch(q) {
   el.innerHTML = '<div class="spinner"></div>';
   try {
     const hiragana = await _romajiToHiragana(q);
-    const [r, r2] = await Promise.all([
+    const isRomaji = /^[a-z\s'-]+$/i.test(q.trim());
+    const [r, r2, romajiIdx] = await Promise.all([
       api('search3', `&query=${encodeURIComponent(q)}&songCount=30&albumCount=10&artistCount=6`),
       hiragana ? api('search3', `&query=${encodeURIComponent(hiragana)}&songCount=20&albumCount=6&artistCount=4`) : Promise.resolve(null),
+      isRomaji ? fetchRomajiIndex() : Promise.resolve(null),
     ]);
     const res  = r.searchResult3  || {};
     const res2 = r2?.searchResult3 || {};
     el.innerHTML = '';
     const artists = _mergeUniq(res.artist||[], res2.artist);
     const albums  = _mergeUniq(res.album ||[], res2.album);
-    const songs   = _mergeUniq(res.song  ||[], res2.song);
+
+    // Merge Navidrome results with romaji index matches
+    const qLow = q.trim().toLowerCase();
+    const romajiHits = romajiIdx
+      ? romajiIdx.filter(e => e.r.includes(qLow))
+      : [];
+    const songs = _mergeUniq(_mergeUniq(res.song||[], res2.song), romajiHits);
+
     if(!artists.length && !albums.length && !songs.length) {
       el.innerHTML = '<div class="empty-state"><div class="icon">🔍</div><p>Keine Ergebnisse</p></div>'; return;
     }