fix(import): stop several entries from claiming one request

README.md

@@ -7,7 +7,7 @@ Sonarr/Radarr-Style Request- & Import-Manager für **Ebooks**, **Comics/Mangas**
 1. **Anfragen**: Im Web-UI per Titel/Autor/ISBN suchen (Ebooks: Open Library · Audiobooks: Audible · Manga: AniList) oder manuell anlegen. Beim Request wählst du die **Ziel-Library** (z.B. deine 8 Bookorbit-Libraries oder die 3 Audiobookshelf-Libraries english/adult/kids). Der Titel erscheint als **Missing**.
    Gehört ein Audiobook-Treffer zu einer Serie, legt **„Ganze Serie…"** alle Folgen auf einmal an (Folgennummer + echter Titel von Audible, optional auf einen Folgenbereich eingegrenzt). Audible hat keine Serien-Abfrage — wordarr sammelt die Folgen über mehrere Suchläufe ein; sollte eine fehlen, zeigt der Dialog die Lücke an.
 2. **Download-Ordner**: wordarr überwacht keinen Downloader aktiv — du legst Dateien selbst in den Download-Ordner (`/mnt/downloads`).
-3. **Import missing**: Im Tab *Import* den Ordner scannen. wordarr schlägt per Fuzzy-Matching Datei→Request-Zuordnungen vor (bei Serien zählt die Folgennummer im Ordnernamen plus der Serienname im Pfad, `???` und `Fragezeichen` gelten als dasselbe); du bestätigst oder korrigierst. Über 🔍 lässt sich zu einem Ordner direkt eine Anfrage suchen — eine führende Folgennummer (`017 - Titel`) wird dabei aus der Suchanfrage genommen, weil Audible sonst schlechter trifft, und stattdessen als Band/Folge übernommen. Beim Import wird die Datei nach dem Namensschema der Library **umbenannt und verschoben**. Ordner mit mehreren Audio-Dateien werden als ein Audiobook behandelt (`Titel - Part 01.mp3`, …). Auch Ordner, die in Disc-Unterordner (`CD`, `CD1`, `CD 2`, `Disc 3`, `Teil 1`) aufgeteilt sind, gelten als **ein** Audiobook — der Ordnername darüber liefert den Titel, die Parts werden über alle Discs hinweg durchnummeriert. Unterordner ohne Audio (`Cover`, Scans, Booklets) werden dabei ignoriert. Liegen die Teile eines Mehrteilers dagegen **nebeneinander** (`100 - Toteninsel Teil 1`, `… Teil 2`, …), markierst du sie und klickst *Ausgewählte zusammenfassen* — sie werden als ein Hörbuch mit durchlaufenden Parts importiert (✂️ löst das wieder auf).
+3. **Import missing**: Im Tab *Import* den Ordner scannen. wordarr schlägt per Fuzzy-Matching Datei→Request-Zuordnungen vor (bei Serien zählt die Folgennummer im Ordnernamen plus der Serienname im Pfad, `???` und `Fragezeichen` gelten als dasselbe); du bestätigst oder korrigierst. Über 🔍 lässt sich zu einem Ordner direkt eine Anfrage suchen — eine führende Folgennummer (`017 - Titel`) wird dabei aus der Suchanfrage genommen, weil Audible sonst schlechter trifft, und stattdessen als Band/Folge übernommen. Beim Import wird die Datei nach dem Namensschema der Library **umbenannt und verschoben**. Ordner mit mehreren Audio-Dateien werden als ein Audiobook behandelt (`Titel - Part 01.mp3`, …). Auch Ordner, die in Disc-Unterordner (`CD`, `CD1`, `CD 2`, `Disc 3`, `Teil 1`) aufgeteilt sind, gelten als **ein** Audiobook — der Ordnername darüber liefert den Titel, die Parts werden über alle Discs hinweg durchnummeriert. Unterordner ohne Audio (`Cover`, Scans, Booklets) werden dabei ignoriert. Mehrteiler in Unterordnern (`Teil A`/`Teil B`, `A - Titel`/`B - Titel`) zählen ebenfalls als ein Hörbuch. Liegen die Teile dagegen **nebeneinander** (`100 - Toteninsel Teil 1`, `… Teil 2`, …), markierst du sie und klickst *Ausgewählte zusammenfassen* — sie werden als ein Hörbuch mit durchlaufenden Parts importiert (✂️ löst das wieder auf). Sind mehrere Einträge derselben Anfrage zugeordnet, fragt wordarr vor dem Import nach und fasst sie zusammen — sonst importiert nur der erste und der Rest scheitert. Fehlt einem bereits importierten Hörbuch später ein Teil, wählst du es im Zuordnungs-Dropdown unter *Bereits importiert — Teile anhängen* (↩︎); die neuen Dateien werden hinten angehängt und alle Tracks neu getaggt.
 
 ## Setup (Docker)
 

static/app.js

@@ -621,6 +621,7 @@ $("#detail-form").addEventListener("submit", async (e) => {
 // ---- import ----
 let scanItems = [];
 let missingReqs = [];
+let importedReqs = [];
 let viewIdx = []; // indices into scanItems after filter/sort
 let importPage = 0;
 const IMPORT_PAGE_SIZE = 25;
@@ -631,9 +632,10 @@ $("#scan-btn").addEventListener("click", async () => {
   $("#scan-info").innerHTML = '<span class="spinner"></span> Scanne…';
   try {
     const split = $("#split-dirs").checked;
-    const [scan, reqs] = await Promise.all([
+    const [scan, reqs, done] = await Promise.all([
       api("/api/import/scan?split_dirs=" + split),
       api("/api/requests?status=missing"),
+      api("/api/requests?status=imported"),
     ]);
     scanItems = scan.items;
     // selection state lives here, not in the DOM, so it survives paging/filtering
@@ -642,6 +644,7 @@ $("#scan-btn").addEventListener("click", async () => {
       item.checked = !!item.suggested_request_id;
     });
     missingReqs = reqs;
+    importedReqs = done;
     importPage = 0;
     $("#scan-info").textContent = `${scan.items.length} Kandidat(en) in ${scan.download_dir}`;
     $("#import-toolbar").hidden = scanItems.length === 0;
@@ -699,13 +702,18 @@ function renderImportTable() {
   tbody.innerHTML = pageIdx
     .map((i) => {
       const item = scanItems[i];
+      const option = (r, suffix = "") =>
+        `<option value="${r.id}" ${r.id === item.request_id ? "selected" : ""}>
+          ${esc(r.title)} — ${esc(r.authors)} (${esc(r.library_name)})${suffix}</option>`;
       const opts = missingReqs
         .filter((r) => r.media_type === item.media_type)
-        .map(
+        .map((r) => option(r))
-          (r) =>
+        .join("");
-            `<option value="${r.id}" ${r.id === item.request_id ? "selected" : ""}>
+      // already imported audiobooks can take further parts (a late CD, or one
-              ${esc(r.title)} — ${esc(r.authors)} (${esc(r.library_name)})</option>`
+      // that failed while its siblings went through)
-        )
+      const appendOpts = importedReqs
+        .filter((r) => r.media_type === item.media_type && r.imported_path)
+        .map((r) => option(r, " ↩︎"))
         .join("");
       return `<tr>
         <td><input type="checkbox" data-check="${i}" ${item.checked ? "checked" : ""}></td>
@@ -716,7 +724,9 @@ function renderImportTable() {
         </td>
         <td>${esc(item.media_type)}</td>
         <td class="row">
-          <select data-select="${i}"><option value="">— überspringen —</option>${opts}</select>
+          <select data-select="${i}"><option value="">— überspringen —</option>${opts}
+            ${appendOpts ? `<optgroup label="Bereits importiert — Teile anhängen">${appendOpts}</optgroup>` : ""}
+          </select>
           <button class="secondary" data-quick="${i}" title="Metadaten suchen und Anfrage direkt verbinden">🔍</button>
           ${item.parts ? `<button class="secondary" data-split="${i}" title="Zusammenfassung wieder auflösen">✂️</button>` : ""}
         </td>
@@ -1002,14 +1012,50 @@ async function pickQuickResult(r) {
 // ---- import execution (batched, with progress) ----
 const IMPORT_BATCH_SIZE = 20;
 
+// several entries on one request means one audiobook split across folders:
+// importing them one by one only imports the first and fails the rest
+function collapseSharedRequests(chosen) {
+  const byRequest = new Map();
+  for (const item of chosen) {
+    const group = byRequest.get(item.request_id);
+    if (group) group.push(item);
+    else byRequest.set(item.request_id, [item]);
+  }
+  const shared = [...byRequest.values()].filter((g) => g.length > 1);
+  if (shared.length) {
+    const names = shared
+      .map((g) => `• ${g.map((it) => it.name).join(" + ")}`)
+      .join("\n");
+    const ok = confirm(
+      `${shared.length} Anfrage(n) sind mehreren Einträgen zugeordnet:\n\n${names}\n\n` +
+        "Als je ein Hörbuch mit durchlaufenden Parts importieren?\n" +
+        "(Abbrechen: nichts wird importiert)"
+    );
+    if (!ok) return null;
+  }
+  return [...byRequest.values()].map((group) => ({
+    path: group.length > 1 ? sharedParent(group) : group[0].path,
+    is_dir: group.length > 1 ? true : group[0].is_dir,
+    files: group.flatMap((it) => it.files),
+    request_id: group[0].request_id,
+    append: importedReqs.some((r) => r.id === group[0].request_id),
+  }));
+}
+
+// deepest folder that holds all of the group's entries
+function sharedParent(group) {
+  const parts = group.map((it) => it.path.split("/"));
+  const first = parts[0];
+  let i = 0;
+  while (i < first.length - 1 && parts.every((p) => p[i] === first[i])) i++;
+  return first.slice(0, i).join("/") || group[0].path;
+}
+
 $("#import-btn").addEventListener("click", async () => {
-  const items = scanItems
+  const chosen = scanItems.filter((item) => item.checked && item.request_id);
-    .filter((item) => item.checked && item.request_id)
+  if (!chosen.length) { toast("Nichts ausgewählt", true); return; }
-    .map((item) => ({
+  const items = collapseSharedRequests(chosen);
-      path: item.path, is_dir: item.is_dir, files: item.files,
+  if (!items) return;
-      request_id: item.request_id,
-    }));
-  if (!items.length) { toast("Nichts ausgewählt", true); return; }
   const btn = $("#import-btn");
   btn.disabled = true;
   const allResults = [];

tests/test_import_flow.py

@@ -538,3 +538,112 @@ def test_merged_parts_clean_up_nested_source_folders(client):
     assert not (base / "A - Sphinx").exists()
     assert not (base / "B - Volk").exists()
     assert (base / "Cover" / "front.jpg").exists()
+
+
+def test_letter_indexed_parts_are_one_audiobook(client):
+    """"Teil A/B/C" and "A - Titel/B - Titel" both describe one story."""
+    schattenwelt = client.downloads / "175 Schattenwelt-3CD-DE-2015-VOiCE"
+    for part in ("Teil A", "Teil B", "Teil C"):
+        d = schattenwelt / part
+        d.mkdir(parents=True)
+        (d / "01.mp3").write_bytes(b"")
+
+    toteninsel = client.downloads / "100 - Toteninsel"
+    for part in ("A - Das.Raetsel.der.Sphinx", "B - Das.vergessene.Volk",
+                 "C - Der Fluch der Graeber"):
+        d = toteninsel / part
+        d.mkdir(parents=True)
+        (d / "01.mp3").write_bytes(b"")
+    (toteninsel / "Cover").mkdir()
+    (toteninsel / "Cover" / "f.jpg").write_bytes(b"")
+
+    items = {i["name"]: i for i in client.get("/api/import/scan").json()["items"]}
+    assert sorted(items) == ["100 - Toteninsel", "175 Schattenwelt-3CD-DE-2015-VOiCE"]
+    for item in items.values():
+        assert item["is_dir"] and len(item["files"]) == 3
+        # parts stay in A, B, C order
+        assert [Path(f).parent.name[0] for f in item["files"]] in (
+            ["T", "T", "T"], ["A", "B", "C"],
+        )
+    order = [Path(f).parent.name for f in items["175 Schattenwelt-3CD-DE-2015-VOiCE"]["files"]]
+    assert order == ["Teil A", "Teil B", "Teil C"]
+
+
+def test_letter_folders_that_are_not_parts_stay_separate(client):
+    """Two episodes that happen to start with a letter must not be merged."""
+    base = client.downloads / "Sammlung"
+    for name in ("A - Erste Folge", "Zweite Folge"):
+        d = base / name
+        d.mkdir(parents=True)
+        (d / "01.mp3").write_bytes(b"")
+        (d / "02.mp3").write_bytes(b"")
+    names = sorted(i["name"] for i in client.get("/api/import/scan").json()["items"])
+    assert names == ["A - Erste Folge", "Zweite Folge"]
+
+
+def test_append_to_an_already_imported_audiobook(client):
+    """The Toteninsel case: part A got imported, B and C failed. They can be
+    added afterwards without moving anything back by hand."""
+    root = client.tmp_path / "library" / "kids"
+    lib_id = client.post("/api/libraries", json={
+        "name": "K", "media_type": "audiobook", "root_path": str(root),
+        "folder_template": "{Title}", "file_template": "{Title}",
+    }).json()["id"]
+    req_id = client.post("/api/requests",
+                         json={"library_id": lib_id, "title": "Toteninsel"}).json()["id"]
+
+    part_a = client.downloads / "A - Sphinx"
+    part_a.mkdir()
+    for i in (1, 2, 3):
+        (part_a / f"{i:02d}.mp3").write_bytes(b"")
+    client.post("/api/import", json={"items": [{
+        "path": str(part_a), "is_dir": True,
+        "files": [str(f) for f in sorted(part_a.iterdir())], "request_id": req_id,
+    }]})
+    imported = client.get("/api/requests", params={"status": "imported"}).json()[0]
+    assert len(list(Path(imported["imported_path"]).iterdir())) == 3
+
+    # B and C arrive later
+    later = []
+    for part in ("B - Volk", "C - Graeber"):
+        d = client.downloads / part
+        d.mkdir()
+        for i in (1, 2):
+            f = d / f"{i:02d}.mp3"
+            f.write_bytes(b"")
+            later.append(str(f))
+    res = client.post("/api/import", json={"items": [{
+        "path": str(client.downloads / "B - Volk"), "is_dir": True,
+        "files": later, "request_id": req_id, "append": True,
+    }]}).json()["results"][0]
+    assert res["ok"] and res["appended"]
+
+    files = sorted(p.name for p in Path(res["dest"]).iterdir())
+    assert files == [f"Toteninsel - Part 0{i}.mp3" for i in range(1, 8)]
+
+
+def test_append_without_the_flag_is_still_refused(client):
+    lib_id = client.post("/api/libraries", json={
+        "name": "K", "media_type": "audiobook", "root_path": str(client.tmp_path / "k"),
+    }).json()["id"]
+    req_id = client.post("/api/requests",
+                         json={"library_id": lib_id, "title": "X"}).json()["id"]
+    folder = client.downloads / "first"
+    folder.mkdir()
+    (folder / "a.mp3").write_bytes(b"")
+    (folder / "b.mp3").write_bytes(b"")
+    client.post("/api/import", json={"items": [{
+        "path": str(folder), "is_dir": True,
+        "files": [str(folder / "a.mp3"), str(folder / "b.mp3")], "request_id": req_id,
+    }]})
+
+    second = client.downloads / "second"
+    second.mkdir()
+    (second / "c.mp3").write_bytes(b"")
+    res = client.post("/api/import", json={"items": [{
+        "path": str(second), "is_dir": False,
+        "files": [str(second / "c.mp3")], "request_id": req_id,
+    }]}).json()["results"][0]
+    assert not res["ok"]
+    assert "bereits importiert" in res["error"]
+    assert (second / "c.mp3").exists()

wordarr/api/imports.py

@@ -30,6 +30,8 @@ class ImportItem(BaseModel):
     is_dir: bool
     files: list[str]
     request_id: int
+    # add to an already imported audiobook instead of importing a new one
+    append: bool = False
 
 
 class ImportIn(BaseModel):
@@ -42,8 +44,28 @@ def do_import(data: ImportIn, session: Session = Depends(get_session)):
     download_root = Path(config.DOWNLOAD_DIR).resolve()
     for item in data.items:
         req = session.get(BookRequest, item.request_id)
-        if not req or req.status != "missing":
+        if not req:
-            results.append({"path": item.path, "ok": False, "error": "request not found or not missing"})
+            results.append({"path": item.path, "ok": False,
+                            "error": f"Anfrage #{item.request_id} existiert nicht mehr"})
+            continue
+        if item.append and req.status == "imported":
+            try:
+                dest = mover.append_to_import(item.files, req, req.library)
+            except Exception as exc:
+                results.append({"path": item.path, "ok": False, "error": str(exc)})
+                continue
+            req.imported_path = dest
+            session.commit()
+            results.append({"path": item.path, "ok": True, "dest": dest, "appended": True})
+            continue
+        if req.status != "missing":
+            # usually several entries pointing at the same request: the first one
+            # imported and flipped it, the rest land here
+            results.append({"path": item.path, "ok": False, "error": (
+                f"Anfrage „{req.title}“ (#{req.id}) ist bereits importiert"
+                f"{' nach ' + req.imported_path if req.imported_path else ''}"
+                " — mehrere Einträge auf dieselbe Anfrage? Dann vorher zusammenfassen."
+            )})
             continue
         # every source path must stay inside the download dir - merged items
         # carry files from several folders, so check them all

wordarr/importer/mover.py

@@ -6,6 +6,27 @@ from ..naming import render_template, sanitize
 from . import tagger
 
 
+def _cleanup_sources(src_dir: Path, paths: list[Path]) -> None:
+    """Remove emptied source folders: the item itself plus every folder the files
+    came from, deepest first - "…/100 - Toteninsel/A - Sphinx/CD" contributes all
+    three. Anything still holding files (cover art, booklets) is left alone, and
+    the download dir itself is never removed."""
+    download_root = Path(config.DOWNLOAD_DIR).resolve()
+    candidates = {src_dir}
+    for p in paths:
+        d = p.parent
+        while d == src_dir or src_dir in d.parents:
+            candidates.add(d)
+            if d == src_dir:
+                break
+            d = d.parent
+    for d in sorted(candidates, key=lambda p: len(p.parts), reverse=True):
+        if d.resolve() == download_root:
+            continue  # merged items can point at the download dir itself
+        if d.is_dir() and not any(f.is_file() for f in d.rglob("*")):
+            shutil.rmtree(d, ignore_errors=True)
+
+
 def import_item(item_path: str, files: list[str], is_dir: bool, request, library) -> str:
     """Move scanned files into the library, renamed per the library's templates.
     Returns the destination path (folder for multi-file audiobooks, else the file)."""
@@ -22,26 +43,7 @@ def import_item(item_path: str, files: list[str], is_dir: bool, request, library
             shutil.move(str(src), dest)
             if request.media_type == "audiobook":
                 tagger.tag_audio(dest, request, track=i, total=len(paths))
-        # remove emptied source folders: the item itself plus the disc/part
+        _cleanup_sources(Path(item_path), paths)
-        # subfolders the files came from, deepest first. Anything still holding
-        # files (cover art, booklets) is left alone.
-        src_dir = Path(item_path)
-        download_root = Path(config.DOWNLOAD_DIR).resolve()
-        # collect every folder the files came from, up to (and including) the
-        # item itself - "…/100 - Toteninsel/A - Sphinx/CD" contributes all three
-        candidates = {src_dir}
-        for p in paths:
-            d = p.parent
-            while d == src_dir or src_dir in d.parents:
-                candidates.add(d)
-                if d == src_dir:
-                    break
-                d = d.parent
-        for d in sorted(candidates, key=lambda p: len(p.parts), reverse=True):
-            if d.resolve() == download_root:
-                continue  # merged items can point at the download dir itself
-            if d.is_dir() and not any(f.is_file() for f in d.rglob("*")):
-                shutil.rmtree(d, ignore_errors=True)
         return str(folder)
 
     src = paths[0]
@@ -52,3 +54,36 @@ def import_item(item_path: str, files: list[str], is_dir: bool, request, library
     if request.media_type == "audiobook":
         tagger.tag_audio(dest, request)
     return str(dest)
+
+
+def append_to_import(files: list[str], request, library) -> str:
+    """Add more files to an audiobook that was already imported - a part that
+    arrived late, or one that failed on the first run. Numbering continues after
+    the files already there, and all tracks are re-tagged with the new total."""
+    dest_dir = Path(request.imported_path or "")
+    if not dest_dir.is_dir():
+        raise FileNotFoundError(
+            f"Zielordner existiert nicht (mehr): {request.imported_path}"
+        )
+    existing = sorted(
+        f for f in dest_dir.iterdir()
+        if f.is_file() and f.suffix.lower() in config.AUDIOBOOK_EXTENSIONS
+    )
+    paths = [Path(f) for f in files]
+    total = len(existing) + len(paths)
+    width = max(2, len(str(total)))
+    base = render_template(library.file_template, request)
+
+    for i, src in enumerate(paths, len(existing) + 1):
+        dest = dest_dir / sanitize(f"{base} - Part {i:0{width}d}{src.suffix.lower()}")
+        if dest.exists():
+            raise FileExistsError(f"Destination already exists: {dest}")
+        shutil.move(str(src), dest)
+        if request.media_type == "audiobook":
+            tagger.tag_audio(dest, request, track=i, total=total)
+    if request.media_type == "audiobook":
+        for i, f in enumerate(existing, 1):
+            tagger.tag_audio(f, request, track=i, total=total)
+    for src_dir in {p.parent for p in paths}:
+        _cleanup_sources(src_dir, paths)
+    return str(dest_dir)

wordarr/importer/scanner.py

@@ -3,13 +3,17 @@ from pathlib import Path
 
 from .. import config
 
-# "CD", "CD1", "CD 2", "Disc_03", "Teil 1", "Part 2" as folder name. The number is
+# "CD", "CD1", "CD 2", "Disc_03", "Teil 1", "Teil B" as folder name. The index is
-# optional (single-disc rips just use "CD"). A bare number is deliberately not a
+# optional (single-disc rips just use "CD") and may be a letter. A bare number is
-# disc: those folders are usually episodes of a series.
+# deliberately not a disc: those folders are usually episodes of a series.
 DISC_DIR_RE = re.compile(
-    r"^(?:cd|disc|disk|dvd|teil|part|vol|volume)[\s._-]*(\d{1,3})?$",
+    r"^(?:cd|disc|disk|dvd|teil|part|vol|volume)[\s._-]*(\d{1,3}|[a-h])?$",
     re.IGNORECASE,
 )
+# "A - Das Raetsel der Sphinx", "B - Das vergessene Volk": parts of one story,
+# told apart only by a leading letter. Only used when *every* audio subfolder
+# follows the pattern.
+LETTER_PART_RE = re.compile(r"^([a-h])\s*[-–—._:]\s*\S", re.IGNORECASE)
 
 
 def media_type_for(ext: str) -> str | None:
@@ -28,13 +32,23 @@ def natural_key(name: str) -> list:
     return [int(p) if p.isdigit() else p.lower() for p in re.split(r"(\d+)", name)]
 
 
+def _index(token: str) -> int:
+    return int(token) if token.isdigit() else ord(token.lower()) - ord("a") + 1
+
+
 def disc_number(name: str) -> int | None:
-    """Disc index of a disc folder name, 0 for an unnumbered "CD". None if the
+    """Disc index of a disc folder name, 0 for an unnumbered "CD", 1-8 for a
-    name is not a disc folder at all."""
+    letter ("Teil B"). None if the name is not a disc folder at all."""
     m = DISC_DIR_RE.match(name.strip())
     if not m:
         return None
-    return int(m.group(1)) if m.group(1) else 0
+    return _index(m.group(1)) if m.group(1) else 0
+
+
+def letter_part(name: str) -> int | None:
+    """Index of an "A - Titel" style part folder, else None."""
+    m = LETTER_PART_RE.match(name.strip())
+    return _index(m.group(1)) if m else None
 
 
 def scan(root: Path, split_dirs: bool = False) -> list[dict]:
@@ -67,14 +81,16 @@ def scan(root: Path, split_dirs: bool = False) -> list[dict]:
         """Audio files of d's disc subfolders ("CD", "CD1", "CD2", …), in disc
         order. Subfolders without audio (Cover, Scans, …) are ignored. None if d
         is not a disc-split folder."""
-        discs = []
+        audio_subs = [s for s in subdirs(d) if has_audio(s)]
-        for s in subdirs(d):
+        # artwork/booklet folders are already filtered out above
-            if not has_audio(s):
+        discs = [(disc_number(s.name), s) for s in audio_subs]
-                continue  # artwork/booklet folder, not part of the audiobook
+        if any(num is None for num, _ in discs):
-            num = disc_number(s.name)
+            # not disc folders - but "A - …", "B - …" are parts of one story too,
-            if num is None:
+            # as long as every single one of them follows that shape
-                return None  # a real subfolder -> not a disc split, walk normally
+            letters = [(letter_part(s.name), s) for s in audio_subs]
-            discs.append((num, s))
+            if len(letters) < 2 or any(num is None for num, _ in letters):
+                return None  # real subfolders -> walk normally
+            discs = letters
         files = []
         for _, s in sorted(discs, key=lambda t: (t[0], natural_key(t[1].name))):
             files.extend(audio_files(s))