NovaSonic/backend/lib/ytdlp.js

const { spawn } = require('child_process');
const path      = require('path');
const fs        = require('fs');
const CONFIG    = require('./config');
const { log }   = require('./jobs');
const {
  sanitize, navidromeArtist,
  downloadArtwork, findExistingTrack,
} = require('./metadata');
const { romajiForStorage, isTokenizerReady } = require('./romaji');

// Matches hiragana, katakana, CJK — used to detect Japanese content
const JP_RE = /[ぁ-んァ-ン一-龯]/;

function buildTitleKeywords(title) {
  // For Japanese titles: Art Tracks on YTM/YouTube are often romanized
  // ("Souiunatsu" for "そういう夏") — a Japanese keyword filter would always
  // reject the correct video. Channel + duration are the quality gates instead.
  if (JP_RE.test(title)) return [];
  const VARIANT_WORDS = new Set(['sped','speedup','slowed','reverb','nightcore','karaoke','parody','remix','cover','acoustic','instrumental']);
  const STOPWORDS = new Set(['the','a','an','and','or','of','in','on','at','to','for','feat','ft','with','single','ep','album','remaster','remastered','deluxe','edition','version','live','bonus']);
  const MIX_QUALIFIERS = ['radio', 'extended', 'club', 'vip', 'original', 'edit'];
  const lower = (title || '').toLowerCase();
  const strippedTitle = (title || '').replace(/\([^)]*\)/g, '').trim();
  const words = strippedTitle
    .replace(/[^\w\s]/g, ' ')
    .split(/\s+/)
    .filter(w => w.length >= 3 && !VARIANT_WORDS.has(w.toLowerCase()) && !STOPWORDS.has(w.toLowerCase()));
  // Numbers are the most distinctive token a title has and they are usually SHORT, so the
  // longest-two rule threw them away: "700 Main Street" kept only Street+Main and happily matched
  // "777 Main Street" by a different artist. Numbers are therefore always required, on top of the
  // two longest words.
  // Ausnahme: die Jahreszahl einer Neuauflage ("… - 2020 Remaster") steht auf der Veroeffentlichung,
  // aber nie im YouTube-Titel — als Pflicht-Keyword wuerde sie den richtigen Upload ablehnen. Nur
  // wenn ein solches Qualifier-Wort daneben steht; ein Titel, der SELBST eine Jahreszahl ist
  // ("1999", "Berlin 2020"), behaelt sie.
  const RELEASE_QUALIFIER = /\b(remaster|remastered|version|edition|anniversary|mono|stereo)\b/i;
  const isEditionYear = w => /^(19|20)\d{2}$/.test(w) && RELEASE_QUALIFIER.test(title || '');
  const isRequiredNum = w => /^\d+$/.test(w) && !isEditionYear(w);
  const numbers = words.filter(isRequiredNum);
  const wordsNoNum = words.filter(w => !isRequiredNum(w));
  const top2 = wordsNoNum.sort((a, b) => b.length - a.length).slice(0, 2);
  // Uploaders abbreviate the same word the release spells out ("700 Main St" vs "700 Main Street"),
  // which rejected the official Art Track in every cascade step. Accept either spelling; \b keeps
  // the short form from matching inside another word.
  const ABBREV = { street: 'st', saint: 'st', mount: 'mt', doctor: 'dr', versus: 'vs', number: 'no' };
  const toPattern = w => {
    const abbr = ABBREV[w.toLowerCase()];
    if (abbr) return `\\b(?:${w}|${abbr})\\b`;
    return (w.length >= 4 && w.endsWith('s')) ? w + '?' : w;
  };
  const result = [...numbers.map(n => `\\b${n}\\b`), ...top2.map(toPattern)];
  const qualifier = lower.includes('mix') ? MIX_QUALIFIERS.find(q => lower.includes(q)) : null;
  if (qualifier && !top2.some(w => w.toLowerCase() === qualifier)) result.push(qualifier);
  return result;
}

// Aus der YTM-Suchausgabe (--flat-playlist --print webpage_url) die Song-URLs herausziehen.
// Eine Suche liefert drei Sorten Zeilen: watch?v=… (ein Song), browse/MPREb_… (ein Album) und
// browse/UC… (ein Kuenstlerkanal). Nur die erste ist ein Kandidat; die anderen beiden sind
// Listeneintraege und werden uebersprungen.
//
// Frueher galt eine browse/UC-Zeile als "yt-dlp hat einen Kanal aufgeklappt" und die GESAMTE
// Trefferliste wurde verworfen — auch die bereits gesammelten Songs davor. Bei "DAT ADAM UFO" stand
// der Kanal auf Platz 9 und riss sieben gute Treffer mit, darunter den offiziellen Art Track auf
// Platz 1; uebrig blieb der YouTube-Fallback, der einen Live-Mitschnitt zog. Aufklappen kann hier
// ohnehin nicht passieren: mit --flat-playlist druckt yt-dlp einen Kanal als EINE Zeile.
function pickYtmVideoUrls(stdout) {
  const urls = [];
  let skipped = 0;
  for (const line of (stdout || '').split('\n')) {
    const u = line.trim();
    if (!u) continue;
    if (u.includes('watch?v=')) urls.push(u);
    else if (u.includes('/browse/')) skipped++;
  }
  return { urls, skipped };
}

function buildVariantFilter(title) {
  const t = (title || '').toLowerCase();
  // !~= (?i) = case-insensitive regex "does not match". Use \b word boundaries so that
  // partial matches like "nightcoreals" containing "nightcore" don't falsely reject results.
  const RULES = [
    { key: 'sped',         expr: 'title !~= (?i)\\bsped\\b' },
    { key: 'speedup',      expr: 'title !~= (?i)\\bspeed.{0,2}up\\b' },
    { key: 'slowed',       expr: 'title !~= (?i)\\bslowed\\b' },
    { key: 'reverb',       expr: 'title !~= (?i)\\breverb\\b' },
    { key: 'nightcore',    expr: 'title !~= (?i)\\bnightcore\\b' },
    { key: 'karaoke',      expr: 'title !~= (?i)\\bkaraoke\\b' },
    { key: 'parody',       expr: 'title !~= (?i)\\bparody\\b' },
    { key: 'remix',        expr: 'title !~= (?i)\\bremix\\b' },
    { key: 'cover',        expr: 'title !~= (?i)\\bcover\\b' },
    { key: 'acoustic',     expr: 'title !~= (?i)\\bacoustic\\b' },
    { key: 'instrumental', expr: 'title !~= (?i)\\binstrumental\\b' },
    // Konzertmitschnitte: `!is_live` heisst nur "laeuft nicht gerade als Stream" und laesst eine
    // Live-AUFNAHME durch. Auf dem echten Kuenstlerkanal ist die sonst nicht vom Studiotrack zu
    // unterscheiden — so landete "Dat Adam - Ufo Video Days 2015 Live" in der Bibliothek.
    // skipRe statt includes(): "deliver"/"delivery" enthalten "live" als Teilstring und wuerden
    // die Regel sonst faelschlich abschalten.
    { key: 'live', expr: 'title !~= (?i)\\blive\\b', skipRe: /\blive\b/i },
  ];
  // Eine Regel entfaellt, wenn der GESUCHTE Titel das Wort selbst traegt — wer "Live Forever" oder
  // bewusst eine Live-Version sucht, soll sie auch bekommen.
  const parts = RULES.filter(r => r.skipRe ? !r.skipRe.test(t) : !t.includes(r.key)).map(r => r.expr);
  return parts.length ? parts.join(' & ') : '';
}

async function downloadTrack({ jobId, artist, rawArtist, albumArtist, title, album, year, trackNum, totalTracks, discNum, discTotal, compilation, genre, artworkUrl, explicit, outputDir, durationMs, sourceUrl }) {
  const mainArtist = albumArtist || artist;

  // If the title or artist contains Japanese characters, wait for kuromoji to finish loading.
  // Without it romajiForStorage returns the original text unchanged, producing Japanese
  // folder/filenames and preventing sort tags from being written.
  if (JP_RE.test(title) || JP_RE.test(rawArtist || artist || '')) {
    if (!isTokenizerReady()) {
      log(jobId, '⏳ Warte auf kuromoji-Tokenizer…');
      await new Promise(resolve => {
        const t0 = Date.now();
        const iv = setInterval(() => {
          if (isTokenizerReady() || Date.now() - t0 > 30000) { clearInterval(iv); resolve(); }
        }, 300);
      });
    }
  }

  // Strip release-type suffixes Spotify appends to track names (e.g. "recognize - Single" → "recognize").
  // Only strip trailing "- word(s)" when those words are release-type qualifiers or bare years, not
  // real sub-titles (which tend to be longer phrases or start with "feat"/"ft").
  // Used for BOTH the filename ("01 - Artist - Title", no "- Single") and the YTM search query.
  const RELEASE_SUFFIX_RE = /\s*[-–]\s*(?:(?:official\s+)?(?:music\s+)?(?:single|ep|lp|album|ost|soundtrack|remaster(?:ed)?|deluxe(?:\s+edition)?|bonus\s+tracks?|b-?sides?|version|edit)\b.*|(?:20|19)\d{2})\s*$/i;
  const cleanTitle = title.replace(RELEASE_SUFFIX_RE, '').trim() || title;

  // Folder / filename: use original names (Japanese or whatever was passed in).
  // Romaji goes ONLY into sort tags (TITLESORT, ARTISTSORT, etc.) via embedMetadata.
  const safeArtist        = sanitize((mainArtist || '').split(/[,;&]/)[0].trim());
  const safeAlbum         = sanitize(album || 'Singles');
  const dir               = path.join(outputDir || CONFIG.musicPath, safeArtist, safeAlbum);
  fs.mkdirSync(dir, { recursive: true });

  const safeTitle          = sanitize(cleanTitle);
  const trackPrefix        = trackNum ? String(trackNum).padStart(2, '0') + ' - ' : '';
  // Filename format: "{01 - }Artist1, Artist2 - Title.ext"
  const safeArtistForFile  = sanitize((artist || '').replace(/;/g, ','));
  const fileBase           = `${trackPrefix}${safeArtistForFile} - ${safeTitle}`;

  const existing = findExistingTrack(outputDir || CONFIG.musicPath, safeArtist, cleanTitle);
  if (existing) {
    log(jobId, `⏭ Bereits vorhanden: ${path.basename(existing)} — übersprungen`);
    return { success: true, dir, skipped: true };
  }

  const outputTemplate = path.join(dir, `${fileBase}.%(ext)s`);
  // For YTM search: use the original (raw) artist when available — the YTM channel is registered
  // under the Japanese/original name, not the iTunes-resolved English name.
  // rawArtist is undefined for non-Japanese tracks, so fall back to mainArtist.
  const ytmArtist    = (rawArtist || mainArtist).replace(/\p{S}/gu, '').trim();
  const searchArtist = ytmArtist;

  const escRe = s => s.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');

  const searchTitle = cleanTitle;

  const variantFilter = buildVariantFilter(searchTitle);
  const titleKws      = buildTitleKeywords(searchTitle);
  const variantPart   = variantFilter ? ` & ${variantFilter}` : '';
  const titleKwPart   = titleKws.length ? titleKws.map(k => ` & title ~= (?i)${k}`).join('') : '';

  // Soft channel check: first word of original artist name used in early cascade steps to avoid
  // downloading a same-title song by a different artist (e.g. wrong "Moonlight" for N!GHT).
  // Skip when artistFirstWord is non-ASCII (Japanese kanji/kana): YouTube channel names are
  // almost never in kanji, so the filter would reject every valid result.
  const artistFirstWord = (rawArtist || mainArtist).split(/[\s,/]+/)[0];
  const artistChannelPart = (artistFirstWord.length >= 3 && !JP_RE.test(artistFirstWord))
    ? ` & channel ~= (?i)${escRe(artistFirstWord)}` : '';
  // yt-dlp fills `artist` (music metadata) on YouTube "Art Tracks" — the label-provided official
  // audio — even when the channel doesn't contain the artist name (BANGTANTV/HYBE/…). Verified with
  // "BTS Pied Piper": ONLY the official upload had artist=BTS; every fan/live/lyric reupload had
  // none. Used as an OR alternative to the channel check so those official uploads still pass strict.
  const artistMetaPart = (artistFirstWord.length >= 3 && !JP_RE.test(artistFirstWord))
    ? ` & artist ~= (?i)${escRe(artistFirstWord)}` : '';

  // Use a space (not " - ") between artist and title: this matches how users type
  // in the YTM search box and ranks the exact official track first. A dash skews
  // YTM ranking toward a same-named artist's full discography.
  const query = `${ytmArtist} ${searchTitle}`;

  const baseArgs = [
    '--extract-audio',
    '--audio-format',   CONFIG.audioFmt,
    '--audio-quality',  CONFIG.audioQuality,
    '-o',               outputTemplate,
    '--no-playlist',
    '--no-warnings',
    '--newline',
    // Hard upper size limit — prevents saving a wrong 28-min video as a ~52 MB mp3
    '--max-filesize',   '30M',
    // Use the web_music player client (falling back to default) so YouTube Music
    // "Art Track" / topic uploads are reachable. The android_vr client returns
    // "This video is not available" for many YTM tracks that play fine in the browser.
    '--extractor-args', 'youtube:player_client=web_music,default',
  ];

  const spawnYtdlp = (args) => new Promise((resolve, reject) => {
    const proc = spawn(CONFIG.ytdlpBin, args, { env: { ...process.env, PYTHONUNBUFFERED: '1' } });
    let stderr = '', lastPct = '';
    proc.stdout.on('data', d => {
      d.toString().split('\n').filter(l => l.trim()).forEach(line => {
        if (line.includes('%') && line === lastPct) return;
        if (line.includes('%')) lastPct = line;
        log(jobId, line.trim());
      });
    });
    proc.stderr.on('data', d => {
      stderr += d.toString();
      d.toString().split('\n')
        .filter(l => l.trim() && !l.startsWith('[debug]'))
        .forEach(l => log(jobId, l.trim()));
    });
    proc.on('error', resolve);
    proc.on('close', code => {
      // Treat all non-zero exits as "no result" so the cascade continues.
      // Fatal errors (network, bad args) are logged via stderr above; hasAudio() decides outcome.
      if (code !== 0 && code !== 101) log(jobId, `⚠️  yt-dlp exit ${code}: ${stderr.slice(-200).trim()}`);
      resolve();
    });
  });

  // Use original (raw) artist for YTM URL — better ranking since channel is in original language.
  // Append the "Songs" filter param so results are restricted to YTM's Songs shelf
  // (no videos/playlists/clips) — the documented way to song-search YTM. This is cleaner
  // for normal tracks; for ambiguous artist names yt-dlp's search may still not surface the
  // exact official track (a known extractor limitation — use the direct link in that case).
  const YTM_SONGS_PARAM = 'EgWKAQIIAWoKEAkQBRAKEAMQBA%3D%3D';
  const ytmQuery = `${rawArtist || mainArtist} ${searchTitle}`;
  const ytmUrl = `https://music.youtube.com/search?q=${encodeURIComponent(ytmQuery)}&params=${YTM_SONGS_PARAM}`;
  const expectedAudio = path.join(dir, `${fileBase}.${CONFIG.audioFmt}`);
  const hasAudio = () => fs.existsSync(expectedAudio);

  // Direct URL download (e.g. SoundCloud) — skip the ytsearch cascade entirely
  if (sourceUrl) {
    log(jobId, `🔗 Direkter Download: ${sourceUrl}`);
    await spawnYtdlp([sourceUrl, '--no-playlist', ...baseArgs]);
    const audioFile = hasAudio() ? expectedAudio : null;
    // Direct-link download failed (e.g. YouTube 403 / bot check) — must report FAILURE, not success.
    // Previously returned { success: true }, so the job was marked "done/Fertig!" and the UI wrongly
    // said the track was added.
    if (!audioFile) { log(jobId, '⚠️  Download fehlgeschlagen'); return { success: false, failed: true, dir }; }
    return embedMetadata({ jobId, audioFile, dir, trackPrefix, safeTitle, rawArtist, artist, mainArtist, album, year, trackNum, totalTracks, discNum, discTotal, compilation, genre, artworkUrl, explicit, title: searchTitle });
  }

  // Fetch YTM search result URLs as a flat list (no channel expansion) and return only
  // actual video URLs (watch?v=…). This prevents yt-dlp from following an artist channel
  // result and treating its uploads as the search result set.
  //
  // NOTE: do NOT check for [youtube:tab] in stderr — that fires for all YTM search
  // page processing, not just channel expansion, and would wrongly return [] always.
  const getYtmVideoUrls = (maxItems) => new Promise(resolve => {
    let out = '';
    const proc = spawn(CONFIG.ytdlpBin, [
      ytmUrl,
      '--flat-playlist',
      '--playlist-items', `1-${maxItems}`,
      '--print', 'webpage_url',
      '--no-warnings',
      // Without the web_music client, yt-dlp parses the YTM search page as a
      // generic YouTube search and returns unrelated videos instead of the
      // native Songs shelf (where the actual artist track lives).
      '--extractor-args', 'youtube:player_client=web_music,default',
    ], { env: { ...process.env, PYTHONUNBUFFERED: '1' } });
    proc.stdout.on('data', d => { out += d.toString(); });
    proc.on('error', () => resolve([]));
    proc.on('close', () => {
      const { urls, skipped } = pickYtmVideoUrls(out);
      if (!urls.length) log(jobId, `⚠️  YTM: keine Song-Treffer (${skipped} Listeneintrag/-eintraege)`);
      else log(jobId, `📡 YTM: ${urls.length} Ergebnis(se) gefunden${skipped ? ` (${skipped} Album/Kanal uebersprungen)` : ''}`);
      resolve(urls);
    });
  });

  const mf = (dur, variant, strict = false) => {
    let durPart;
    if (dur) {
      durPart = `duration > ${dur.min} & duration < ${dur.max} & `;
    } else if (durationMs) {
      // Even when relaxing the window (Mittelweg), keep a 2× cap so a 28-min video can't slip through
      durPart = `duration < ${Math.round(durationMs / 1000 * 2)} & `;
    } else {
      durPart = '';
    }
    const base = `${durPart}!is_live${titleKwPart}${variant ? variantPart : ''}`;
    // Non-strict, or no artist constraint (short / Japanese name): single filter.
    if (!strict || !artistChannelPart) return ['--match-filter', base];
    // Strict: pass if the channel name matches the artist OR yt-dlp's music `artist` metadata does
    // (catches official label-channel uploads like BANGTANTV). Two --match-filter args = OR in yt-dlp.
    return [
      '--match-filter', `${base}${artistChannelPart}`,
      '--match-filter', `${base}${artistMetaPart}`,
    ];
  };

  const PI_FILTERED    = ['--playlist-items', '1-5',  '--max-downloads', '1'];
  const PI_FILTERED_10 = ['--playlist-items', '1-10', '--max-downloads', '1'];
  const PI_UNFILTERED  = ['--playlist-items', '1'];

  // Fetch YTM URLs once upfront so every cascade step filters the SAME result set.
  // Re-fetching produced different orderings, causing the correct video (found in step 1
  // but failing the channel filter) to disappear by step 3 and a wrong one to slip through.
  const ytmUrls = await getYtmVideoUrls(10);
  const tryYtm = async (n, mfArgs) => {
    const urls = n ? ytmUrls.slice(0, n) : ytmUrls;
    if (!urls.length) return;
    await spawnYtdlp([...urls, '--max-downloads', '1', ...mfArgs, ...baseArgs]);
  };

  if (durationMs && durationMs > 30000) {
    const durationSec = Math.round(durationMs / 1000);
    const margin = Math.max(10, Math.round(durationSec * 0.10));
    const dur = { min: Math.max(30, durationSec - margin), max: durationSec + margin };

    log(jobId, `🔍 Suche YT Music (~${durationSec}s ±${margin}s): "${query}"`);
    // 1. YTM top-5 — strict: duration + title + variant + channel check
    await tryYtm(5, mf(dur, true, true));
    if (!hasAudio()) {
      // 2. YT top-5 — strict: same filters including channel check
      log(jobId, '⚠️  Kein YTM-Treffer — Fallback zu YouTube…');
      await spawnYtdlp([`ytsearch5:${query}`, ...PI_FILTERED, ...mf(dur, true, true), ...baseArgs]);
    }
    if (!hasAudio()) {
      // 3. YTM all-10 — no channel check (label channels, etc.)
      log(jobId, '⚠️  Erweitere Suche auf top 10 mit Dauerbeschränkung…');
      await tryYtm(0, mf(dur, true));
    }
    if (!hasAudio()) {
      // 4. YT top-10 — no channel check
      await spawnYtdlp([`ytsearch10:${query}`, ...PI_FILTERED_10, ...mf(dur, true), ...baseArgs]);
    }
    // No duration match. "Mittelweg": relax the duration constraint but REQUIRE the artist
    // channel (+ title). This catches legit tracks whose YT upload duration drifts from the
    // iTunes value, while never grabbing a same-titled video by someone else. If nothing
    // matches title+channel we download NOTHING and the job fails cleanly (see end of fn) —
    // far better than silently saving the wrong song (e.g. a "recognize" fan clip).
    if (!hasAudio()) {
      // 5. YTM all — no duration, but channel + title required
      log(jobId, '⚠️  Kein Treffer im Dauerbereich — suche ohne Dauer, aber mit Künstler-Channel…');
      await tryYtm(0, mf(null, true, true));
    }
    if (!hasAudio()) {
      // 6. YT top-10 — no duration, but channel + title required
      await spawnYtdlp([`ytsearch10:${query}`, ...PI_FILTERED_10, ...mf(null, true, true), ...baseArgs]);
    }
  } else {
    log(jobId, `🔍 Suche YT Music: "${query}"`);
    // 1. YTM top-5 — strict: title + variant + channel check
    await tryYtm(5, mf(null, true, true));
    if (!hasAudio()) {
      // 2. YT top-5 — strict
      await spawnYtdlp([`ytsearch5:${query}`, ...PI_FILTERED, ...mf(null, true, true), ...baseArgs]);
    }
    if (!hasAudio()) {
      // 3. YTM all-10 — no channel check (catches label/distributor channels)
      await tryYtm(0, mf(null, true));
    }
    if (!hasAudio()) {
      // 4. YT top-5 — no channel check
      await spawnYtdlp([`ytsearch5:${query}`, ...PI_FILTERED, ...mf(null, true), ...baseArgs]);
    }
    // Mittelweg (no-duration): after step 4, do NOT fall through to title-only or
    // no-filter grabs — those pull wrong covers (observed: Yorushika → Piano Echoes).
    // Fail cleanly, same as the with-duration branch. Use the Direktlink instead.
  }

  const audioFile = hasAudio() ? expectedAudio : null;
  if (!audioFile) {
    log(jobId, '⚠️  Nicht eindeutig gefunden — bitte Direktlink im Importer nutzen');
    return { success: false, notFound: true, dir };
  }

  return embedMetadata({ jobId, audioFile, dir, trackPrefix, safeTitle, rawArtist, artist, mainArtist, album, year, trackNum, totalTracks, discNum, discTotal, compilation, genre, artworkUrl, explicit, title: searchTitle });
}

// Shared ffmpeg metadata embedding — used by both yt-dlp and squid paths
async function embedMetadata({ jobId, audioFile, dir, trackPrefix, safeTitle, rawArtist, artist, mainArtist, album, year, trackNum, totalTracks, discNum, discTotal, compilation, genre, artworkUrl, explicit, title }) {
  const coverPath = await downloadArtwork(artworkUrl, dir);
  const hasCover = !!(coverPath && fs.existsSync(coverPath));

  log(jobId, `🏷  Metadaten + Cover → ${path.basename(audioFile)}`);

  const fileExt = path.extname(audioFile);
  const tmpFile = audioFile.slice(0, -fileExt.length) + '.metatmp' + fileExt;
  await new Promise(resolve => {
    const ffArgs = ['-i', audioFile];
    if (hasCover) ffArgs.push('-i', coverPath);
    ffArgs.push('-map', '0:a');
    if (hasCover) ffArgs.push('-map', '1:v');
    // Main tags: store original text (Japanese or whatever was passed in).
    // rawArtist = original Spotify/source artist (may be Japanese); artist = iTunes-resolved (may be English).
    // Use rawArtist for the per-track artist tag; mainArtist for album_artist so all tracks
    // in an album get the same value (prevents Navidrome album-splitting).
    const tagArtist      = navidromeArtist(rawArtist || artist);
    const tagAlbumArtist = mainArtist.replace(/\s+&\s+/g, ', ');
    // Sort tags: romaji for display / sorting in apps that support them (TITLESORT, ARTISTSORT, etc.)
    // artist is already the iTunes-resolved English name when available — use directly (more accurate
    // than kuromoji). For non-iTunes tracks romajiForStorage acts as kuromoji fallback.
    const sortTitle       = romajiForStorage(title)                                        || title;
    const sortArtist      = romajiForStorage(navidromeArtist(artist))                     || navidromeArtist(artist);
    const sortAlbumArtist = romajiForStorage(mainArtist.replace(/\s+&\s+/g, ', '))        || mainArtist.replace(/\s+&\s+/g, ', ');
    const sortAlbum       = album ? (romajiForStorage(album) || album) : null;
    ffArgs.push(
      '-c',             'copy',
      '-map_metadata',  '-1',
      '-id3v2_version', '3',
      '-metadata', `title=${title}`,
      '-metadata', `artist=${tagArtist}`,
      '-metadata', `album_artist=${tagAlbumArtist}`,
    );
    // Always write an album tag, defaulting to "Singles" so it matches the on-disk folder
    // (album || 'Singles'). Without this, no-album tracks land in a "Singles" folder but show
    // as "[Unknown Album]" in Navidrome — a tag/folder mismatch that breaks the metadata editor.
    ffArgs.push('-metadata', `album=${album || 'Singles'}`);
    // Sort tags — only write when they differ from main (no-op for non-Japanese tracks)
    if (sortTitle       !== title)         ffArgs.push('-metadata', `TITLESORT=${sortTitle}`);
    if (sortArtist      !== tagArtist)     ffArgs.push('-metadata', `ARTISTSORT=${sortArtist}`);
    if (sortAlbumArtist !== tagAlbumArtist) ffArgs.push('-metadata', `ALBUMARTISTSORT=${sortAlbumArtist}`);
    if (sortAlbum && sortAlbum !== album)  ffArgs.push('-metadata', `ALBUMSORT=${sortAlbum}`);
    if (year)        ffArgs.push('-metadata', `date=${String(year)}`);
    if (trackNum)    ffArgs.push('-metadata', `track=${totalTracks ? `${trackNum}/${totalTracks}` : String(trackNum)}`);
    if (totalTracks) ffArgs.push('-metadata', `totaltracks=${String(totalTracks)}`);
    if (genre)       ffArgs.push('-metadata', `genre=${genre}`);
    if (discNum)     ffArgs.push('-metadata', `disc=${discTotal ? `${discNum}/${discTotal}` : String(discNum)}`);
    if (compilation) ffArgs.push('-metadata', `compilation=1`);
    if (explicit)    ffArgs.push('-metadata', 'ITUNESADVISORY=1');
    if (hasCover) {
      ffArgs.push(
        '-metadata:s:v', 'title=Album cover',
        '-metadata:s:v', 'comment=Cover (front)',
      );
    }
    ffArgs.push(tmpFile, '-y');

    const ff = spawn('ffmpeg', ffArgs);
    let ffErr = '';
    ff.stderr.on('data', d => ffErr += d.toString());
    ff.on('error', () => resolve());
    ff.on('close', code => {
      if (code === 0 && fs.existsSync(tmpFile)) {
        fs.renameSync(tmpFile, audioFile);
        if (hasCover) try { fs.unlinkSync(coverPath); } catch {}
        const base = path.basename(audioFile, path.extname(audioFile));
        for (const ext of ['webm', 'webm.part', 'm4a', 'opus']) {
          try { fs.unlinkSync(path.join(dir, `${base}.${ext}`)); } catch {}
        }
        log(jobId, `✅ Fertig${hasCover ? ' (Cover 1000x1000 eingebettet)' : ''}`);
      } else {
        try { fs.unlinkSync(tmpFile); } catch {}
        log(jobId, `⚠️  ffmpeg code ${code}`);
        if (ffErr) log(jobId, ffErr.slice(-200));
      }
      resolve();
    });
  });

  return { success: true, dir };
}

module.exports = { downloadTrack, embedMetadata, buildTitleKeywords, buildVariantFilter, pickYtmVideoUrls };