feat(folder_library): Folder Library core plugin (#610)

Adds the bundled Folder Library plugin (browse the DLC library by its on-disk
folder tree, in-app folder CRUD, drag-and-drop + dialog song moves, sort/filter,
live search), wired into the classic v2 toolbar and the v3 Songs page.

Includes the screen.js IIFE dedup (unified surface factory) and review fixes:
path-traversal guard on /song/move, folder-delete data-loss fix, plural
/api/plugins/<id> namespace, loose-folder song recognition, error-text escaping,
v3 setLibView null-guard, and tests.

Co-authored-by: Kyle <kyle.j.t@live.co.uk>
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

plugins/folder_library/routes.py

@@ -0,0 +1,440 @@
+"""
+Folder Library plugin — routes.py
+
+Surfaces the DLC folder structure as a navigable tree and provides in-app
+folder management (create / rename / delete) and song moves. Every filesystem
+mutation is confined to DLC_DIR and validated against path traversal.
+"""
+
+from pathlib import Path
+from fastapi import APIRouter, Request
+from fastapi.responses import JSONResponse
+import shutil
+import re
+
+
+# ── Pure, testable helpers ─────────────────────────────────────────────────
+
+_UNSAFE_NAME_RE = re.compile(r'[\\/:*?"<>|]')
+
+
+def _safe_name(name: str) -> bool:
+    """A single path segment is safe: no separators, no traversal dot-names,
+    no surrounding whitespace, no characters illegal across filesystems."""
+    if not name or name.strip() != name:
+        return False
+    if _UNSAFE_NAME_RE.search(name):
+        return False
+    if name in (".", ".."):
+        return False
+    return True
+
+
+def _safe_path(path_str: str) -> bool:
+    """A slash-separated path is safe iff every segment is a safe name."""
+    if not path_str:
+        return False
+    return all(_safe_name(p) for p in path_str.split("/"))
+
+
+def _is_within(root: Path, candidate: Path) -> bool:
+    """True iff ``candidate`` resolves to a location inside ``root`` (after
+    normalising ``..`` and symlinks). Containment backstop for file moves so a
+    crafted filename can't escape DLC_DIR even past the segment validator."""
+    try:
+        candidate.resolve().relative_to(root.resolve())
+        return True
+    except (ValueError, OSError):
+        return False
+
+
+def _path_to_dir(root: Path, folder_path: str) -> Path:
+    """Resolve a slash-separated folder path relative to ``root``."""
+    result = root
+    for part in folder_path.split("/"):
+        result = result / part
+    return result
+
+
+def _load_is_loose_song():
+    """The host's authoritative loose-folder predicate (lib/loosefolder.py),
+    imported lazily so the plugin still loads if it's ever unavailable. A
+    loose-folder song is a directory carrying audio + an arrangement XML rather
+    than a ``.sloppak`` bundle, so the plain suffix check below misses it."""
+    try:
+        from loosefolder import is_loose_song
+        return is_loose_song
+    except Exception:
+        return None
+
+
+_IS_LOOSE_SONG = _load_is_loose_song()
+
+
+def _is_song(p: Path) -> bool:
+    """A song carrier is a ``.sloppak`` / ``.feedpak`` file or directory-form
+    bundle (extension on the leaf name), or a host-recognised loose-folder song
+    directory — so loose-folder charts surface in the tree like any other song
+    instead of being walked into as if they were ordinary folders."""
+    if p.suffix.lower() in (".sloppak", ".feedpak"):
+        return True
+    if _IS_LOOSE_SONG is not None and p.is_dir():
+        try:
+            return bool(_IS_LOOSE_SONG(p))
+        except Exception:
+            return False
+    return False
+
+
+def setup(app, context):
+    log = context["log"]
+    router = APIRouter(prefix="/api/plugins/folder_library")
+
+    # ── Two-level cache ────────────────────────────────────────────────
+    # _meta_cache  — expensive extract_meta() results keyed by abs path
+    #                (as_posix() string).  Never cleared; keys are updated
+    #                in-place when files are moved so the data stays valid.
+    # _cache       — tree structure ("folders" / "root_songs").  Cleared on
+    #                every mutation so the next /tree request rebuilds it —
+    #                but that rebuild is now fast because _meta_cache is warm.
+    _cache      = {}   # "tree" → JSONResponse-ready dict
+    _meta_cache = {}   # abs_posix_path → extracted meta (no filename/added)
+
+    def _invalidate():
+        """Clear the tree structure cache only.  _meta_cache is preserved."""
+        _cache.clear()
+
+    def _dlc_root() -> Path | None:
+        try:
+            return Path(context["get_dlc_dir"]())
+        except Exception:
+            return None
+
+    def _scan_root(dlc: Path) -> Path:
+        sloppak = dlc / "sloppak"
+        return sloppak if sloppak.exists() else dlc
+
+    def _meta(p: Path, dlc: Path) -> dict:
+        # filename and added are always computed fresh — they change when files move.
+        try:
+            filename = "/".join(p.relative_to(dlc).parts)
+        except ValueError:
+            filename = p.name
+        added = None
+        try:
+            added = p.stat().st_mtime
+        except Exception:
+            pass
+
+        # Return cached extracted metadata if available.
+        cache_key = p.as_posix()
+        if cache_key in _meta_cache:
+            m = dict(_meta_cache[cache_key])   # shallow copy
+            m["filename"] = filename
+            m["added"]    = added
+            return m
+
+        # Cache miss — run the expensive extract.
+        m = {"title": None, "artist": None, "album": None, "duration": None,
+             "year": None, "tuning": None, "arrangements": [], "stems": [], "lyrics": False}
+        try:
+            raw = context["extract_meta"](p)
+            if raw:
+                m["title"]    = raw.get("title")    or raw.get("name")
+                m["artist"]   = raw.get("artist")   or raw.get("artistName")
+                m["album"]    = raw.get("album")     or raw.get("albumName")
+                m["duration"] = raw.get("duration")
+                m["year"]     = raw.get("year")
+                m["tuning"]   = raw.get("tuning")
+
+                # arrangements — objects with a "name" key e.g. [{name:"Lead",...}, ...]
+                raw_arr = raw.get("arrangements") or []
+                if isinstance(raw_arr, (list, tuple)):
+                    m["arrangements"] = [
+                        a["name"] if isinstance(a, dict) else str(a)
+                        for a in raw_arr
+                        if (isinstance(a, dict) and "name" in a) or isinstance(a, str)
+                    ]
+
+                # stems — may also be objects with a "name" key, same as arrangements
+                raw_stems = raw.get("stems") or []
+                for _key in ("stems", "stem_types", "available_stems", "stemTypes"):
+                    _v = raw.get(_key)
+                    if _v:
+                        raw_stems = _v
+                        break
+                if isinstance(raw_stems, (list, tuple)):
+                    m["stems"] = [
+                        a["name"] if isinstance(a, dict) else str(a)
+                        for a in raw_stems
+                        if (isinstance(a, dict) and "name" in a) or isinstance(a, str)
+                    ]
+
+                # lyrics — try common key variants
+                for _key in ("lyrics", "hasLyrics", "has_lyrics", "lyric", "hasLyric"):
+                    _val = raw.get(_key)
+                    if _val is not None:
+                        if isinstance(_val, str):
+                            m["lyrics"] = _val.lower() not in ("", "false", "no", "0")
+                        else:
+                            m["lyrics"] = bool(_val)
+                        break
+        except Exception as exc:
+            log.debug("meta failed for %s: %s", p.name, exc)
+        if not m["title"]:
+            m["title"] = p.stem
+
+        _meta_cache[cache_key] = m      # store without filename/added
+        result = dict(m)
+        result["filename"] = filename
+        result["added"]    = added
+        return result
+
+    def _scan_dir(path: Path, root: Path, dlc: Path) -> dict:
+        """Recursively scan a directory and return a folder node."""
+        songs = []
+        children = []
+        try:
+            for entry in sorted(path.iterdir(), key=lambda p: p.name.lower()):
+                if entry.name.startswith("."):
+                    continue
+                if _is_song(entry):
+                    songs.append(_meta(entry, dlc))
+                elif entry.is_dir():
+                    children.append(_scan_dir(entry, root, dlc))
+        except PermissionError:
+            log.warning("permission denied: %s", path)
+        try:
+            rel = path.relative_to(root)
+            folder_path = "/".join(rel.parts)
+        except ValueError:
+            folder_path = path.name
+        return {
+            "name": path.name,
+            "path": folder_path,
+            "songs": songs,
+            "children": children,
+        }
+
+    def _apply_tree_filters(tree, arrangements_has="", arrangements_lacks="",
+                            stems_has="", stems_lacks="", has_lyrics="", tunings=""):
+        """Filter a cached tree dict by arrangement/stem/lyrics/tuning params.
+        The cache always holds the full unfiltered tree; this is applied per-request."""
+        def _split(s):
+            return [x.strip().lower() for x in s.split(",") if x.strip()] if s else []
+
+        arr_has   = _split(arrangements_has)
+        arr_lacks = _split(arrangements_lacks)
+        st_has    = _split(stems_has)
+        st_lacks  = _split(stems_lacks)
+        tun_set   = set(_split(tunings))
+        lyr       = None if has_lyrics == "" else (has_lyrics == "1")
+
+        if not any([arr_has, arr_lacks, st_has, st_lacks, tun_set, lyr is not None]):
+            return tree  # no filters active — return as-is
+
+        def _song_ok(s):
+            arrs = [a.lower() for a in (s.get("arrangements") or [])]
+            stms = [x.lower() for x in (s.get("stems") or [])]
+            if arr_has   and not any(a in arrs for a in arr_has):   return False
+            if arr_lacks and     any(a in arrs for a in arr_lacks): return False
+            if st_has    and not any(x in stms for x in st_has):    return False
+            if st_lacks  and     any(x in stms for x in st_lacks):  return False
+            if lyr is not None and bool(s.get("lyrics")) != lyr:    return False
+            if tun_set and (s.get("tuning") or "").lower() not in tun_set: return False
+            return True
+
+        def _filter_node(node):
+            return {
+                "name": node["name"],
+                "path": node["path"],
+                "songs": [s for s in node["songs"] if _song_ok(s)],
+                "children": [_filter_node(c) for c in node.get("children", [])],
+            }
+
+        return {
+            "folders": [_filter_node(f) for f in tree["folders"]],
+            "root_songs": [s for s in tree["root_songs"] if _song_ok(s)],
+        }
+
+    @router.get("/tree")
+    def get_tree(
+        arrangements_has:   str = "",
+        arrangements_lacks: str = "",
+        stems_has:          str = "",
+        stems_lacks:        str = "",
+        has_lyrics:         str = "",
+        tunings:            str = "",
+    ):
+        if "tree" not in _cache:
+            dlc = _dlc_root()
+            if not dlc or not dlc.exists():
+                return JSONResponse({"folders": [], "root_songs": [],
+                                     "error": "DLC directory not found"})
+            root = _scan_root(dlc)
+            log.info("folder_library: scanning %s", root)
+            folders = []
+            root_songs = []
+            try:
+                for entry in sorted(root.iterdir(), key=lambda p: p.name.lower()):
+                    if entry.name.startswith("."):
+                        continue
+                    if _is_song(entry):
+                        root_songs.append(_meta(entry, dlc))
+                    elif entry.is_dir():
+                        folders.append(_scan_dir(entry, root, dlc))
+            except PermissionError:
+                return JSONResponse({"folders": [], "root_songs": [],
+                                     "error": "Permission denied"})
+            _cache["tree"] = {"folders": folders, "root_songs": root_songs}
+
+        result = _apply_tree_filters(
+            _cache["tree"], arrangements_has, arrangements_lacks,
+            stems_has, stems_lacks, has_lyrics, tunings,
+        )
+        return JSONResponse(result)
+
+    @router.post("/folder/create")
+    async def create_folder(request: Request):
+        body = await request.json()
+        name = (body.get("name") or "").strip()
+        parent = (body.get("parent") or "").strip()
+        if not _safe_name(name):
+            return JSONResponse({"error": "Invalid folder name"}, status_code=400)
+        if parent and not _safe_path(parent):
+            return JSONResponse({"error": "Invalid parent path"}, status_code=400)
+        dlc = _dlc_root()
+        if not dlc:
+            return JSONResponse({"error": "DLC dir not found"}, status_code=500)
+        root = _scan_root(dlc)
+        parent_dir = _path_to_dir(root, parent) if parent else root
+        if parent and not parent_dir.exists():
+            return JSONResponse({"error": "Parent folder not found"}, status_code=404)
+        target = parent_dir / name
+        if target.exists():
+            return JSONResponse({"error": "Folder already exists"}, status_code=400)
+        try:
+            target.mkdir(parents=False)
+            _invalidate()
+            return JSONResponse({"ok": True})
+        except Exception as e:
+            return JSONResponse({"error": str(e)}, status_code=500)
+
+    @router.post("/folder/rename")
+    async def rename_folder(request: Request):
+        body = await request.json()
+        old = (body.get("old") or "").strip()
+        new = (body.get("new") or "").strip()
+        if not _safe_path(old) or not _safe_name(new):
+            return JSONResponse({"error": "Invalid folder name"}, status_code=400)
+        dlc = _dlc_root()
+        if not dlc:
+            return JSONResponse({"error": "DLC dir not found"}, status_code=500)
+        root = _scan_root(dlc)
+        src = _path_to_dir(root, old)
+        dst = src.parent / new  # rename within the same parent
+        if not src.exists():
+            return JSONResponse({"error": "Folder not found"}, status_code=404)
+        if dst.exists():
+            return JSONResponse({"error": "Name already taken"}, status_code=400)
+        try:
+            # Pre-compute meta cache key updates (keys change because the
+            # folder path changes — all files under src get a new prefix).
+            old_prefix = src.as_posix() + "/"
+            new_prefix = dst.as_posix() + "/"
+            meta_updates = {
+                key: new_prefix + key[len(old_prefix):]
+                for key in list(_meta_cache)
+                if key.startswith(old_prefix)
+            }
+            src.rename(dst)
+            _invalidate()
+            for old_key, new_key in meta_updates.items():
+                if old_key in _meta_cache:
+                    _meta_cache[new_key] = _meta_cache.pop(old_key)
+            return JSONResponse({"ok": True})
+        except Exception as e:
+            return JSONResponse({"error": str(e)}, status_code=500)
+
+    @router.post("/folder/delete")
+    async def delete_folder(request: Request):
+        body = await request.json()
+        name = (body.get("name") or "").strip()
+        if not _safe_path(name):
+            return JSONResponse({"error": "Invalid folder path"}, status_code=400)
+        dlc = _dlc_root()
+        if not dlc:
+            return JSONResponse({"error": "DLC dir not found"}, status_code=500)
+        root = _scan_root(dlc)
+        target = _path_to_dir(root, name)
+        if not target.exists():
+            return JSONResponse({"error": "Folder not found"}, status_code=404)
+        try:
+            # Relocate every song (at any depth) up to the scan root BEFORE
+            # removing the folder. Colliding filenames are de-duplicated so a
+            # name clash never leaves a song behind to be destroyed by rmtree
+            # (the folder is advertised as "moves its songs to Unsorted").
+            for song_path in sorted(target.rglob("*")):
+                if not song_path.exists():
+                    continue  # a parent song-dir was already relocated
+                if not _is_song(song_path):
+                    continue
+                old_key = song_path.as_posix()
+                dest = root / song_path.name
+                if dest.exists():
+                    stem, suffix = song_path.stem, song_path.suffix
+                    n = 1
+                    while dest.exists():
+                        dest = root / f"{stem} ({n}){suffix}"
+                        n += 1
+                song_path.rename(dest)
+                if old_key in _meta_cache:
+                    _meta_cache[dest.as_posix()] = _meta_cache.pop(old_key)
+            shutil.rmtree(target)
+            _invalidate()
+            return JSONResponse({"ok": True})
+        except Exception as e:
+            return JSONResponse({"error": str(e)}, status_code=500)
+
+    @router.post("/song/move")
+    async def move_song(request: Request):
+        body = await request.json()
+        filename = (body.get("filename") or "").strip()
+        dest_folder = (body.get("folder") or "").strip()
+        # Validate the source path like the folder ops, AND confirm it resolves
+        # inside DLC_DIR — without this a filename such as "../../etc/passwd"
+        # would be renamed (moved) into the served library and become readable.
+        if not filename or not _safe_path(filename):
+            return JSONResponse({"error": "Invalid filename"}, status_code=400)
+        dlc = _dlc_root()
+        if not dlc:
+            return JSONResponse({"error": "DLC dir not found"}, status_code=500)
+        src = dlc / Path(*filename.split("/"))
+        if not _is_within(dlc, src):
+            return JSONResponse({"error": "Invalid filename"}, status_code=400)
+        if not src.exists():
+            return JSONResponse({"error": "Song not found"}, status_code=404)
+        root = _scan_root(dlc)
+        if dest_folder:
+            if not _safe_path(dest_folder):
+                return JSONResponse({"error": "Invalid folder path"}, status_code=400)
+            dst_dir = _path_to_dir(root, dest_folder)
+            if not dst_dir.exists():
+                return JSONResponse({"error": "Destination folder not found"}, status_code=404)
+        else:
+            dst_dir = root
+        dst = dst_dir / src.name
+        if dst.exists():
+            return JSONResponse({"error": "File already exists at destination"}, status_code=400)
+        try:
+            old_key = src.as_posix()
+            src.rename(dst)
+            if old_key in _meta_cache:
+                _meta_cache[dst.as_posix()] = _meta_cache.pop(old_key)
+            _invalidate()
+            return JSONResponse({"ok": True})
+        except Exception as e:
+            return JSONResponse({"error": str(e)}, status_code=500)
+
+    app.include_router(router)
+    log.info("folder_library routes registered")