Lets users pick which providers' cover art to use and in what priority,
generalizing the single prefer_caa_art toggle into an ordered, mix-and-match
list (Sokhi's request). Fully opt-in: default album_art_order is [], so every
existing install is byte-for-byte unchanged until the user enables sources.
How it works:
- Per album, walk the user's ordered sources top-to-bottom; the first source
that actually has THIS album's cover wins. A miss falls through to the next;
if all miss, the download's own art is kept (today's default). The worst case
is always exactly the cover you'd get today -- never wrong art, never an
error into the download.
- Connection-gated: a source is only tried when the user is connected to it
(free sources CAA/Deezer/iTunes/AudioDB always; Spotify only when
authenticated). Tidal/Qobuz/HiFi deferred (cover-URL construction + no clean
core accessor -- not shipping unverified extraction).
- Album-match validated: a source's art is used only when the album it returns
matches the requested artist+album (significant-token subset, tolerant of
Deluxe/Remastered/articles/feat./multi-artist). A loose top search hit for a
different record is treated as a miss -> guarantees no wrong-album art.
- The list supersedes the legacy prefer_caa_art toggle: when album_art_order is
non-empty it is the sole authority (add 'caa' to the list to use Cover Art
Archive), and prefer_caa_art is neutralized for both the embedded-tag art and
cover.jpg paths. With an empty list, prefer_caa_art behaves exactly as before.
Implementation:
- core/metadata/art_sources.py: pure resolver -- effective_art_order (config +
legacy back-compat) and resolve_cover_art (ordered walk + fallback,
exception-safe per source). No network/config/DB; fully unit-testable.
- core/metadata/art_lookup.py: availability gating, per-source lookups against
existing clients (Deezer/iTunes/AudioDB/Spotify search + CAA via MBID),
album-match validation, per-album caching, and select_preferred_art_url --
the single gate the pipeline calls (no-op unless an explicit list is set).
- core/metadata/artwork.py: wired into embed_album_art_metadata and
download_cover_art, gated so no configured list == current behavior.
- web_server.py: GET /api/metadata/art-sources (connected sources only).
- config/settings.py: default album_art_order: [].
- webui (index.html + settings.js): reorderable list in Core Features reusing
the hybrid-source-list pattern + real service logos (with emoji fallback);
load/save wired through the existing metadata_enhancement settings flow.
loadArtSourceOrder populates the saved order synchronously (filtered to known
sources, not availability) so a save before the availability fetch resolves,
or a temporarily-disconnected source, can never wipe the saved order.
Tests: 40 unit/seam tests (resolver ordering/fallback/back-compat, availability,
per-source extraction, album-match validation incl. wrong-album/wrong-artist
rejection, caching, exception-safety, the off-by-default gate). Full metadata
suite still green (610 passed) -- the gated integration changes nothing when no
list is configured.
Note: the settings UI (DOM-heavy, not unit-testable in the JS harness) and the
live per-source art-fetch quality are validated by manual testing.
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