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feat(feed): genre affinity scoring for the for-you feed #951

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dylanjeffers merged 1 commit into from
Jun 12, 2026
+125 −7
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feat(feed): genre affinity scoring for the for-you feed #951

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60 changes: 53 additions & 7 deletions api/v1_users_feed_for_you.go
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Original file line number Diff line number Diff line change
Expand Up @@ -72,10 +72,17 @@ type GetUsersFeedForYouParams struct {
// // tracks the user already heard recently stay in
// // the feed but rank below fresh content. Playlists
// // always get 1.00 (no per-user playlist play data).
// genre_affinity = 0.85 + 0.45 * min(genre_share / 0.30, 1)
// // genre_share is the fraction of my recent plays
// // in the track's genre: a genre at >= 30% of my
// // listening gets the full 1.30x, genres I never
// // play get 0.85x. Neutral 1.00 for playlists,
// // genre-less tracks, and cold-start users with
// // no play history.
//
// final_score = (0.55 * recency_score + 0.45 * engagement_score)
// * social_boost * source_weight * content_type_weight
// * repeat_penalty
// * repeat_penalty * genre_affinity
//
// 3. FILTERS — applied once after the union to keep the candidate set
// cheap:
Expand Down Expand Up @@ -187,6 +194,28 @@ func (app *ApiServer) v1FeedForYou(c *fiber.Ctx) error {
WHERE created_at >= NOW() - INTERVAL '14 days'
GROUP BY track_id
),
-- Genre mix of my recent listening: share = fraction of my recent
-- plays that landed in each genre. Feeds the genre_affinity
-- multiplier so tracks in genres I play often rank higher and
-- genres I never touch rank slightly lower.
--
-- Bounded like the other play sub-selects: only the most recent
-- slice of plays is scanned, so a heavy listener can't pull this
-- CTE wide.
my_genre_affinity AS (
SELECT t.genre,
COUNT(*)::double precision / SUM(COUNT(*)) OVER () AS share
FROM (
SELECT play_item_id AS track_id
FROM plays
WHERE user_id = @userId
ORDER BY created_at DESC
LIMIT 1000
) p
JOIN tracks t ON t.track_id = p.track_id
WHERE t.genre IS NOT NULL AND t.genre <> ''
GROUP BY t.genre
),
-- Per-owner engagement strength: saves+reposts of any of their
-- tracks/playlists by me, plus plays of their tracks. Used for the
-- social_boost multiplier.
Expand Down Expand Up @@ -402,14 +431,17 @@ func (app *ApiServer) v1FeedForYou(c *fiber.Ctx) error {
COALESCE(at.repost_count, 0) AS repost_count,
COALESCE(ap.count, 0) AS play_count,
COALESCE(maa.affinity, 0) AS affinity,
mrp.last_played_at AS last_played_at
mrp.last_played_at AS last_played_at,
t.genre AS genre,
mga.share AS genre_share
FROM candidates c
JOIN tracks t ON t.track_id = c.entity_id
JOIN users u ON u.user_id = t.owner_id
LEFT JOIN aggregate_track at ON at.track_id = c.entity_id
LEFT JOIN aggregate_plays ap ON ap.play_item_id = c.entity_id
LEFT JOIN my_artist_affinity maa ON maa.artist_id = t.owner_id
LEFT JOIN my_recent_plays mrp ON mrp.track_id = c.entity_id
LEFT JOIN my_genre_affinity mga ON mga.genre = t.genre
WHERE c.entity_type = 'track'
AND t.is_current = true
AND t.is_delete = false
Expand Down Expand Up @@ -441,7 +473,9 @@ func (app *ApiServer) v1FeedForYou(c *fiber.Ctx) error {
COALESCE(ap.repost_count, 0) AS repost_count,
0 AS play_count,
COALESCE(maa.affinity, 0) AS affinity,
NULL::timestamp AS last_played_at
NULL::timestamp AS last_played_at,
NULL::text AS genre,
NULL::double precision AS genre_share
FROM candidates c
JOIN playlists p ON p.playlist_id = c.entity_id
JOIN users u ON u.user_id = p.playlist_owner_id
Expand All @@ -461,11 +495,13 @@ func (app *ApiServer) v1FeedForYou(c *fiber.Ctx) error {
),
filtered AS (
SELECT entity_type, entity_id, owner_id, created_at, source,
save_count, repost_count, play_count, affinity, last_played_at
save_count, repost_count, play_count, affinity, last_played_at,
genre, genre_share
FROM filtered_tracks
UNION ALL
SELECT entity_type, entity_id, owner_id, created_at, source,
save_count, repost_count, play_count, affinity, last_played_at
save_count, repost_count, play_count, affinity, last_played_at,
genre, genre_share
FROM filtered_playlists
),
scored AS (
Expand Down Expand Up @@ -496,7 +532,17 @@ func (app *ApiServer) v1FeedForYou(c *fiber.Ctx) error {
WHEN f.last_played_at >= NOW() - INTERVAL '7 days' THEN 0.25
WHEN f.last_played_at >= NOW() - INTERVAL '14 days' THEN 0.50
ELSE 1.00
END AS repeat_penalty
END AS repeat_penalty,
CASE
-- Playlists carry no single genre; genre-less tracks
-- and cold-start users (no genre history at all) are
-- neutral rather than penalized.
WHEN f.entity_type <> 'track' THEN 1.00
WHEN f.genre IS NULL OR f.genre = '' THEN 1.00
WHEN NOT EXISTS (SELECT 1 FROM my_genre_affinity) THEN 1.00
WHEN f.genre_share IS NULL THEN 0.85
ELSE 0.85 + 0.45 * LEAST(f.genre_share / 0.30, 1.0)
END AS genre_affinity
FROM filtered f
),
final_scored AS (
Expand All @@ -507,7 +553,7 @@ func (app *ApiServer) v1FeedForYou(c *fiber.Ctx) error {
created_at,
(0.55 * recency_score + 0.45 * engagement_score)
* social_boost * source_weight * content_type_weight
* repeat_penalty AS score
* repeat_penalty * genre_affinity AS score
FROM scored
),
capped AS (
Expand Down
72 changes: 72 additions & 0 deletions api/v1_users_feed_for_you_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -370,6 +370,78 @@ func TestV1FeedForYou_OldPlaysDoNotSuppress(t *testing.T) {
"a 20-day-old play is outside the window and should not downrank track 101")
}

// feedForYouGenreFixtures returns the standard fixture graph with
// genres on the two in-network sibling tracks: 101 (the naturally
// stronger one) is Rock, 102 is Electronic. Track 666 is an old upload
// (outside every candidate window) that exists only to receive plays
// that shape the viewer's genre mix.
func feedForYouGenreFixtures() database.FixtureMap {
fixtures := feedForYouFixtures()
for _, tr := range fixtures["tracks"] {
switch tr["track_id"] {
case 101:
tr["genre"] = "Rock"
case 102:
tr["genre"] = "Electronic"
}
}
fixtures["tracks"] = append(fixtures["tracks"], map[string]any{
"track_id": 666, "owner_id": 3, "title": "old electronic upload",
"genre": "Electronic",
"created_at": time.Now().Add(-100 * 24 * time.Hour),
})
return fixtures
}

// TestV1FeedForYou_GenreAffinityBoostsFavoredGenre asserts the
// genre_affinity multiplier: the viewer's recent plays are 100%
// Electronic, so Electronic track 102 (1.30x) should outrank its
// naturally-stronger Rock sibling 101 (0.85x, unfamiliar genre) —
// while 101 stays in the feed rather than being filtered.
func TestV1FeedForYou_GenreAffinityBoostsFavoredGenre(t *testing.T) {
app := emptyTestApp(t)
app.skipAuthCheck = true

fixtures := feedForYouGenreFixtures()
// Plays of old track 666 build an all-Electronic genre profile.
// 666 is 100 days old: outside the artist-affinity 90-day window
// and outside every candidate source, so the only signal these
// plays add is genre. The plays are 30+ days old so the repeat
// penalty (14-day window) is not in play either.
plays := make([]map[string]any, 0, 5)
for i := 0; i < 5; i++ {
plays = append(plays, map[string]any{
"id": i + 1, "user_id": 1, "play_item_id": 666,
"created_at": time.Now().Add(-time.Duration(30+i) * 24 * time.Hour),
})
}
fixtures["plays"] = plays
database.Seed(app.pool.Replicas[0], fixtures)

pos := feedForYouTrackPositions(t, app, 101, 102)
require.NotEqual(t, -1, pos[102], "favored-genre track 102 should be in the feed")
require.NotEqual(t, -1, pos[101],
"unfamiliar-genre track 101 should stay in the feed, just ranked lower")
assert.Greater(t, pos[101], pos[102],
"Electronic track 102 should outrank Rock sibling 101 for an all-Electronic listener")
}

// TestV1FeedForYou_GenreAffinityNeutralOnColdStart asserts that a user
// with no play history gets no genre boost or penalty: 101 keeps its
// natural position above 102 even though genres differ.
func TestV1FeedForYou_GenreAffinityNeutralOnColdStart(t *testing.T) {
app := emptyTestApp(t)
app.skipAuthCheck = true

database.Seed(app.pool.Replicas[0], feedForYouGenreFixtures())

pos := feedForYouTrackPositions(t, app, 101, 102)
require.NotEqual(t, -1, pos[101])
require.NotEqual(t, -1, pos[102])
assert.Less(t, pos[101], pos[102],
"with no play history genre_affinity must be neutral; 101 keeps its natural rank")
}

// TestV1FeedForYou_PerArtistCapIsShared asserts that max_per_artist
// applies across both tracks and playlists for the same owner — the
// diversity cap is shared, not per-type. User 2 (followed) has 2 tracks
Expand Down
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