Server half of #367. Web UI follows.
Genres are exposed AS-IS per the operator: split on the delimiter, trimmed,
but no case folding and no synonym mapping. So "Rock" and "rock" appear as
separate rows, as does "Rock/Pop" alongside "Rock" and "Pop". The raw spread
has to be visible before anyone can judge whether it needs normalising, and
the alternative is a mapping table to invent and then maintain.
Trimming is not an exception to that. Splitting "Rock; Pop" yields " Pop", and
showing that as a genre distinct from "Pop" would be a bug in OUR splitting,
not fidelity to the operator's tags.
## The correctness trap this had to avoid
ListAlbumsByGenre compared tracks.genre verbatim, while recommendation.sql and
discover.sql have always split it on [;,]. Building the browse index by
splitting while matching exactly would have listed genres whose pages are
empty — every multi-genre track unreachable from either of its genres.
So ListAlbumsByGenre now splits too. That also fixes Subsonic
getAlbumList?type=byGenre, its only caller, which silently missed every
multi-genre track. Its Genre param went *string → string as a result.
EXISTS rather than JOIN + DISTINCT ON throughout: the lateral split emits one
row per (track, fragment), so a join multiplies rows per album and needs
DISTINCT to undo itself. EXISTS asks the question directly, and the count
query then matches the list query by construction rather than by coincidence.
## Genre is a query parameter, not a path segment
Because "Rock/Pop" is a real ID3 tag — the one the task itself cites — and a
slash cannot survive a path segment: Go normalises %2F and the router would
split the value in two. So filtering rides GET /api/library/albums?genre=,
which also reuses the existing paged album surface instead of adding a
parallel one.
Endpoints:
GET /api/library/genres unpaged index + track counts
GET /api/library/years unpaged index + album counts
GET /api/library/albums?genre= filtered page
GET /api/library/albums?year_from=&year_to= filtered page, either edge open
The indexes are unpaged deliberately: a client needs the whole set to render a
browsable picker, and paging would let it show only a prefix of an ordering
the user didn't choose.
Two refusals rather than guesses: genre+year together is a 400 (the UI browses
them as separate axes, and quietly dropping half a filter would report a
narrower result than it returned), and an inverted year range is a 400 rather
than being silently swapped.
Undated albums are absent from the year axis rather than bucketed under 0 —
"unknown" is not a year, and a 0 row would sort to one end of a chronological
list looking like data.
Tests: parseYearFilter is pure and runs in the fast lane. The integration
tests assert the thing that would otherwise be silently broken — that a
"Rock;Pop" track is reachable from BOTH genres, that "Rock/Pop" survives as a
filter value, that fragment whitespace is trimmed, and that undated albums
stay out of every year range. Reused the existing seedAlbum/seedTrackWithGenre
fixtures, which already took exactly the year and genre arguments needed.
Implements the paged alpha-sorted album list endpoint used by the M6a
wrapping-grid SPA page. Mirrors handleListArtists alpha branch using
ListAlbumsAlphaWithArtist + CountAlbums; 2/2 integration tests pass.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
bvandeusen
