minstrel/internal/playlists/discover_taste_db_test.go

package playlists_test

import (
	"context"
	"fmt"
	"testing"

	"github.com/jackc/pgx/v5/pgtype"
	"github.com/jackc/pgx/v5/pgxpool"

	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
)

func setGenre(t *testing.T, pool *pgxpool.Pool, trackID pgtype.UUID, genre string) {
	t.Helper()
	if _, err := pool.Exec(context.Background(),
		`UPDATE tracks SET genre = $2 WHERE id = $1`, trackID, genre); err != nil {
		t.Fatalf("set genre: %v", err)
	}
}

func seedTasteTag(t *testing.T, pool *pgxpool.Pool, userID pgtype.UUID, tag string, weight float64) {
	t.Helper()
	if _, err := pool.Exec(context.Background(),
		`INSERT INTO taste_profile_tags (user_id, tag, weight) VALUES ($1, $2, $3)
		 ON CONFLICT (user_id, tag) DO UPDATE SET weight = EXCLUDED.weight`,
		userID, tag, weight); err != nil {
		t.Fatalf("seed taste tag: %v", err)
	}
}

// TestListTasteUnheardTracksForDiscover_CapsBeforeLimit is the deploy's shape
// (#5356): one artist whose every track carries the whole taste profile
// outscores everything on summed weight. Capped only after the LIMIT, that
// artist took all 120 rows and the bucket shrank to its 3. Capped before, the
// artist keeps 3 and the single-tag artists below it fill the rest.
func TestListTasteUnheardTracksForDiscover_CapsBeforeLimit(t *testing.T) {
	pool := newPool(t)
	ctx := context.Background()
	u := seedUser(t, pool, "tastecap")

	profile := []string{"Lo-Fi", "Downtempo", "Hip Hop", "Instrumental", "Chillwave"}
	for _, tag := range profile {
		seedTasteTag(t, pool, u.ID, tag, 10)
	}
	allTags := "Lo-Fi; Downtempo; Hip Hop; Instrumental; Chillwave"

	// 13 albums x 10 tracks = 130, more than the query's LIMIT of 120.
	heavy := seedTrack(t, pool, "Heavy 0", "Heavy Artist")
	setGenre(t, pool, heavy.ID, allTags)
	album := heavy.AlbumID
	for i := 1; i < 130; i++ {
		if i%10 == 0 {
			album = seedAlbumForArtist(t, pool, fmt.Sprintf("Heavy Album %d", i/10), heavy.ArtistID)
		}
		tr := seedTrackForArtist(t, pool, fmt.Sprintf("Heavy %d", i), album, heavy.ArtistID)
		setGenre(t, pool, tr.ID, allTags)
	}

	// Twelve artists with one track each, matching a single profile tag.
	const light = 12
	for i := 0; i < light; i++ {
		tr := seedTrack(t, pool, fmt.Sprintf("Light %d", i), fmt.Sprintf("Light Artist %d", i))
		setGenre(t, pool, tr.ID, profile[i%len(profile)])
	}

	rows, err := dbq.New(pool).ListTasteUnheardTracksForDiscover(ctx, dbq.ListTasteUnheardTracksForDiscoverParams{
		UserID: u.ID, DateSeed: "2026-10-08", MaxPerAlbum: 2, MaxPerArtist: 3,
	})
	if err != nil {
		t.Fatalf("list taste unheard: %v", err)
	}

	perArtist := map[pgtype.UUID]int{}
	perAlbum := map[pgtype.UUID]int{}
	for _, r := range rows {
		perArtist[r.ArtistID]++
		perAlbum[r.AlbumID]++
	}
	if got := perArtist[heavy.ArtistID]; got != 3 {
		t.Errorf("heavy artist rows = %d, want exactly the artist cap of 3", got)
	}
	for id, n := range perAlbum {
		if n > 2 {
			t.Errorf("album %v has %d rows, over the album cap of 2", id, n)
		}
	}
	if got, want := len(perArtist), 1+light; got != want {
		t.Errorf("distinct artists = %d, want %d (the heavy artist plus every single-tag artist)", got, want)
	}
	if got, want := len(rows), 3+light; got != want {
		t.Errorf("rows = %d, want %d", got, want)
	}
	// Still ranked by weight: the heavy artist's three lead.
	for i := 0; i < 3 && i < len(rows); i++ {
		if rows[i].ArtistID != heavy.ArtistID {
			t.Errorf("row %d is not the heavy artist's; higher summed weight should rank first", i)
		}
	}
}