# CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

## What this is

LinTunes is an iTunes-replacement music library manager and player for Linux,
built with PyQt6 / Qt Multimedia. It imports an iTunes 12 library, stores the
library as plain JSON (syncable via Syncthing), and reproduces the iTunes UI
(left sidebar + right playlist view, column browser, customizable per-playlist
columns). `spec.md` is the original design brief; `TASKS.md` is the live backlog
and `tasks-done.md` records completed work.

## Commands

```sh
pip install -e .                 # install deps (PyQt6, mutagen, numpy, requests)
python3 -m lintunes.main         # run the app straight from the checkout
python3 -m pytest                # run the whole test suite
python3 -m pytest tests/test_round9.py            # one test file
python3 -m pytest tests/test_round9.py::test_name # one test
```

The app needs a `--data-dir`; config persists to `~/.config/lintunes/config.json`.
One-time iTunes import:

```sh
lintunes --import-xml "iTunes Library.xml" \
         --music-root "/path/to/iTunes Media" \
         --data-dir /path/to/library-data --save-config
```

Runtime needs FFmpeg codecs for Qt Multimedia (`qt6-qtmultimedia` w/ ffmpeg).
Tests run headless via the `qapp` fixture in `tests/conftest.py`
(`QT_QPA_PLATFORM=offscreen`).

## Architecture

**Data flows in one direction through three layers:** storage (JSON on disk) →
model (`Library`/`Track`/`Playlist` dataclasses) → `LibraryManager` (mutations +
persistence) → GUI (Qt widgets that read the manager and connect to its signals).

- **`lintunes/main.py`** — CLI entry. `--import-xml` runs a headless import and
  exits; otherwise `run_gui()` resolves Syncthing conflicts, loads the library,
  builds `Preferences`/`LibraryManager`/`LastFm`/`MainWindow`, wires MPRIS, and
  installs the window as a global event filter (for media keys).

- **`lintunes/models/`** — pure dataclasses (`track.py`, `playlist.py`,
  `library.py`) with `to_dict`/`from_dict` round-tripping. `PlaylistType` is
  `REGULAR | FOLDER | SMART | SYSTEM`. Per-playlist `PlaylistSettings` holds
  visible columns / sort column / widths. Playlists are identified by an 8-char
  hex `persistent_id` (folder containment via `parent_persistent_id`).

- **`lintunes/storage/json_storage.py`** — the library is **multiple files** in
  the data dir: `library.json` (all tracks), `library_metadata.json`, one
  `playlists/<persistent_id>.json` per playlist, and one
  `plays/<machine-id>.json` per machine. Writes are atomic (`*.json.tmp`
  → rename). **`storage/conflict_resolver.py`** merges Syncthing
  `*.sync-conflict-*` files on startup: play counts take the max, edited fields
  take the newest, playlist membership takes the union. Since Round 39 that
  union is **anchor-based** (`merge_track_order`): a track only one copy has is
  re-inserted after the nearest track both share, not appended at the tail, so
  a middle insert stays in the middle. Whose order wins is decided by
  `Playlist.date_modified` — bumped *only* in
  `LibraryManager._set_track_ids` — not by the file's mtime, which moves for
  cosmetic reasons. `library_manager._reconcile_playlist` uses the same helper
  for the live-reload path.

- **`lintunes/storage/play_journal.py`** — why play counts can't conflict. Since
  Round 38 `library.json` holds only a **base** count and each machine owns
  `plays/<machine-id>.json` with *its own* per-track totals; effective count =
  base + the sum of every journal. Only the owner ever writes its journal, so
  two machines never touch the same file — and finishing a track no longer
  rewrites 15 MB, which is what handed Syncthing a conflict once per song.
  Totals, not an append log, so there is no compaction step to double-count in.
  `PlayJournal.load()` must be handed a library whose tracks still carry **base**
  counts (the fresh load at startup, the `disk` copy inside `reload_from_disk`) —
  folding an already-folded library promotes the effective count to base.
  Mirror-image rule in `json_storage.save_tracks()`: it writes
  `journal.base_fields(tid)`, never the `Track`'s effective count. Those two
  places are the whole hazard; `tests/test_round38.py` pins both.

- **`lintunes/library_manager.py`** — `LibraryManager(QObject)` owns the
  `Library`, is the single funnel for all mutations, and persists them
  **debounced** (3 s) with per-area dirty tracking (a play-count bump rewrites
  only `library.json`; a playlist edit rewrites only that playlist file). User
  edits go through `undo_stack` (Ctrl+Z); the internal `_apply_*`/`_set_*`
  helpers do the real mutation + dirty-mark + signal and are reused by undo/redo
  without recursing. Widgets react to its signals (`playlists_changed`,
  `playlist_content_changed(pid)`, `track_updated(id)`, `track_fields_edited`).

- **`lintunes/player.py`** — `Player(QObject)` walks a queue through a swappable
  **`PlaybackSink`**. Player owns the queue, shuffle walk, per-track start/stop
  times and the play-count/scrobble bookkeeping; a sink owns only "make this file
  come out of something, and report where it's up to". `LocalSink` (the
  `QMediaPlayer`/`QAudioOutput` pipeline, with the `QAudioBufferOutput` PCM tee
  that feeds the visualizer) **stays in `player.py`** — the Player tests stub Qt
  Multimedia with `patch.multiple(player_module, QMediaPlayer=..., …)`, so those
  names must resolve in this module. `cast/sink.py::CastSink` is the other
  implementation. `set_sink()` carries the current track, position and
  playing-state across a swap and deliberately does *not* re-emit
  `track_changed` (that would double-scrobble the same song).
  Player is also deliberately **context-agnostic**: playback *context*
  ("library" / "playlist:<pid>") is tracked in `MainWindow`, not the player.

- **`lintunes/gui/`** — `main_window.py` assembles a top `TransportBar` over a
  horizontal `QSplitter` (`SidebarPanel` | stacked `LibraryView`/`PlaylistView`).
  `track_table.py` is the shared track grid (drag/drop, copy/paste, drop
  indicator). `playlist_ops.py::add_tracks_with_dup_check` is the single funnel
  for every add-to-playlist path. `theme.py` applies the palette (highlight
  colors, UI scales) from prefs.

- **`lintunes/importers/itunes_importer.py`** — parses the iTunes XML plist.
  Remaps Mac `file:///Volumes/...` paths to the local `--music-root` with
  case/Unicode-normalization fuzzy matching (macOS is case-insensitive + NFD vs
  ext4). Imports user playlists, folders **and smart playlists** (criteria
  parsed by `smart.parse_itunes_smart`; criteria it can't model are kept as a
  static snapshot — `report.smart_unsupported`). System playlists are skipped
  (`report.skipped_system`). Album art is read live from embedded ID3 tags
  (`tagging.py`), never stored in the library JSON.

- **`lintunes/preferences.py`** — app settings in `<data_dir>/preferences.json`
  (rides the same Syncthing share). `Preferences.set(key, value)` saves and emits
  `changed`; `MainWindow._on_prefs_changed` re-applies theme/metrics live.
  Because it is synced, **anything machine-specific belongs in `config.py`'s
  `config.json` instead** (see `music_folder.py`). `now_playing_font` has three
  states — `None` automatic (best available from `theme.NOW_PLAYING_FALLBACKS`),
  `""` the app font, or an explicit family. Startup never prompts for it; the
  row in Preferences is the only place it's chosen.

- **`lintunes/music_folder.py`** — where the organized tree lives *on this
  machine*. The library stores it three ways (`models/library.py`):
  `music_folder` absolute (what pre-0.10 code reads — kept forever as the shared
  floor between versions), `music_folder_rel` relative to the data dir (the
  portable one, same trick as `Track.location`), and `music_folder_set_at`, a
  stamp so a merge prefers the newest *setting* rather than the newest *file*.
  `resolve()` tries rel → legacy → the per-machine override in `config.json`,
  and every candidate must **exist** — the override is consulted last so a
  machine that once needed one isn't pinned to it forever. Two rules that bite:
  `LibraryManager.set_music_folder` must call `mark_library_settings_dirty()`
  (without it `reload_from_disk` reverts the change on the next sync tick), and
  `organize_root()` can return `None`, which every caller must handle rather
  than inventing a relative path — `MainWindow._music_import_dir` used to fall
  back to `Path("Music")`, which resolved against a working directory GNOME's
  dash doesn't set predictably.

- **`lintunes/mpris.py`** — registers `org.mpris.MediaPlayer2.lintunes` over D-Bus
  so the desktop's media keys / now-playing popup control playback. Spacebar and
  arrow keys are handled locally via `MainWindow.eventFilter`.

- **`lintunes/trash.py`** — freedesktop.org Trash spec 1.0, hand-rolled (no new
  dep). The trash is **per-filesystem**: music usually lives on a mounted volume,
  so the file belongs in `<topdir>/.Trash-<uid>` with a *topdir-relative*,
  percent-encoded `Path=`, not in `~/.local/share/Trash` (which would be a
  cross-device copy the file manager can't "Restore"). The `.trashinfo` is
  created with `O_EXCL` **first** to claim the name atomically, then the file is
  renamed in; a failed rename unlinks the info file so there's never a
  half-trashed pair. Raises `TrashError` without touching the file, so a caller
  can treat failure as "not deleted". Only `LibraryManager` calls it.

- **`lintunes/device_sync.py`** — one-way playlist sync to the Rabbit R1 (Device
  menu). The Rabbit mounts via **MTP/gvfs** (a FUSE path under
  `/run/user/<uid>/gvfs`), not mass storage — so plain file I/O, but never
  copystat and never trust mtimes (diff by name+size). Sync owns exactly
  `Music/<Playlist Name>/` on the device (creates/overwrites/deletes there,
  plus an Auxio-importable `.m3u`); it never deletes outside that folder and
  only ever *reads* local library files.

- **`lintunes/export/`** — `File → Export Playlist…` (also on a playlist's
  right-click menu). A sibling of `device_sync`, reusing its filename helpers
  and `build_m3u`: pure `plan_export()` first, then `ExportWorker` on a daemon
  thread. Two destinations — a **folder** (files as `Artist - Title.ext` plus an
  `.m3u`) or a **web mix** (`index.html` + `audios/` + hero image, from
  `templates/`; **no m3u** — it's a folder you upload, not one you open in a
  player, so `plan.m3u_name` is `""` there). **The manifest is written last**,
  so an interrupted export never leaves a page or m3u naming files that aren't
  there. `web_support.py`
  is the format gate, shaped like `cast/support.py`: deny-by-default on the
  suffix with the iTunes `kind` breaking the `.m4a` tie. **Bitrate never
  triggers a conversion** — only unplayability does — and every conversion
  targets **FLAC**, so it can't cost a bit; DRM'd tracks are reported, never
  attempted. ffmpeg is the *CLI binary* here (not Qt's ffmpeg backend), so it's
  detected at runtime and its absence is offered as "export without them".
  The templates ship a ~180-line dependency-free `player.js`/`player.css` that
  replaced audio.js + jQuery (abandoned since 2012; jQuery was only ever glue —
  audio.js never used it). `player-graphics.gif` must ship **byte-identical**:
  it's an animated GIF whose loading frame is a spinner, not a flat sprite
  sheet — which is why Round 41 recolors its pale glyphs to black with
  `filter: brightness(0)` in CSS rather than editing the file. The one
  user-chosen color (link/row hover backgrounds + the progress fill) travels as
  a `:root { --accent }` custom property declared in `index.html`, so
  `player.css` can read it while staying a verbatim `shutil.copyfile` — the page
  is still the only rendered template. `exporter.normalize_accent` is a hard
  gate, not politeness: the value lands raw inside a `<style>` block and
  `string.Template` escapes nothing. The accent is **not** persisted, so an
  untouched export still renders the original `#8c764a`. Templates are
  registered in `setup.py` via `package_data`; loaded with
  `importlib.resources` so an installed copy finds them.

- **`lintunes/cast/`** — Chromecast playback (Connections menu), using the
  **media-receiver model**: `server.py` runs a `ThreadingHTTPServer` on an
  ephemeral port for the life of a session and the device fetches the *original*
  file itself (bit-exact, no transcode). URLs carry an opaque random token, never
  a path, so traversal is structurally impossible; Range + HEAD are mandatory
  (the device seeks by re-requesting ranges and won't report a duration without
  them). A token resolves to an `_Asset` that is either a file on disk (audio)
  or an in-memory blob (album art, which lives in tags rather than as its own
  file); the two have **separate eviction rings** so a cover can't push out the
  previous track's audio. Art is passed as `play_media(thumb=…)`, which
  pychromecast folds into `metadata["images"]` — that's what a TV paints
  full-screen. `support.py` is the format gate — ALAC, AIFF and protected AAC are
  refused and Player skips them with a status-bar message. `discovery.py` wraps
  `CastBrowser`; `sink.py` is the `PlaybackSink`; `controller.py` owns the
  session and its own `SleepInhibitor`. **pychromecast is imported lazily**, never
  at module scope, so the app still launches where the dep isn't installed yet.
  While casting there is no local PCM, so the **visualizer panel doubles as the
  cast indicator**: it shows the cast glyph instead of bars and a click there
  stops casting (the brightness cycle is suppressed — it means nothing with no
  bars). That is the only cast control in the transport bar. Position comes from
  a 500 ms poll of `adjusted_current_time` (only trusted while PLAYING — it
  creeps while paused).

## Conventions & gotchas

- **Tests are organized as `tests/test_roundN.py`** — each development round adds
  a new `test_roundN.py` alongside the topical files (`test_models.py`,
  `test_itunes_importer.py`, etc.). New feature work follows the same pattern.
- **Keep `Player` and `track_table` manager-free where they already are** —
  cross-cutting data is injected via callbacks/signals (e.g. `track_table` takes
  a `playlists_for_track` callback rather than importing the manager).
- **Cosmetic table settings must not look like edits.** The last column is
  stretch-sized, so Qt re-fires `sectionResized` for it on every viewport width
  change; `track_table._on_section_resized` ignores that section, or resizing
  the window would rewrite the open playlist's JSON (and hand Syncthing a
  conflict) purely for a width `apply_settings` overrides on load anyway.

- **Qt/Wayland gotchas (GNOME/Mutter):** `QDrag.setPixmap` / `setDragCursor` /
  `QCursor.pos()` are unreliable during a drag — `gui/drag_ghost.py` paints its
  own child-widget overlay instead. `QAudioOutput` must not be constructed before
  a `QMainWindow` exists (Qt 6.10 deadlock). Some PyQt signal relays need explicit
  types/lambdas.
- **Music files are only touched deliberately:** tag edits via `tagging.py`,
  and — since Round 18 — artist/album_artist/album edits relocate the file
  inside `LibraryManager.organize_root()` (`<music_folder>/Music`) to keep the
  tree organized iTunes-style (`_maybe_move_file`; undoable; files outside the
  root are never moved; the new path syncs cross-machine via the `location`
  newest-wins merge in `conflict_resolver`). Since Round 33 the *only* other
  path is an explicit user delete (`LibraryManager.delete_tracks`), which moves
  the file to the desktop trash via `trash.py` — never `unlink`, so it stays
  recoverable. Nothing else may move, rewrite or remove music files. The library
  JSON is the source of truth for everything else.
- **Versioning & self-update:** `__version__` in `lintunes/__init__.py` is
  the single source of truth (`setup.py` regex-reads it, never imports the
  package). Claude bumps minor for feature rounds and patch for fix-only
  rounds as part of each round's final commit; trav decides major bumps. The
  status-bar version button (`gui/version_button.py` + `lintunes/updater.py`)
  checks `origin` shortly after launch and every 4 h, and a click runs
  `git pull --ff-only` then re-execs the app — pushing `master` is
  effectively releasing to the other machines (a new pip dependency still
  needs a manual `pip install -e .` there). **Every round ends with commit
  AND push** (trav's standing request, 2026-07-03: both machines ride the
  bleeding edge, sync as often as possible) — so never leave master in a
  half-working state between commits you push.
- `scripts/` holds one-off maintenance tools (`audit_artwork.py`,
  `recover_artwork.py`, `clear_computed_ratings.py`) run manually against a data
  dir; most default to dry-run and need `--write` to mutate files.
- **Not under version control until recently** — the `*~` files are editor
  backups (gitignored). `data/` and `itunes-test-library/` are gitignored (the
  user's real library + large import fixture).