minstrel/internal/playlists/discover_test.go

package playlists

import (
	"testing"

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

// uuidN generates a deterministic pgtype.UUID from an integer for cap tests.
func uuidN(n int) pgtype.UUID {
	var u pgtype.UUID
	u.Valid = true
	u.Bytes[15] = byte(n)
	u.Bytes[14] = byte(n >> 8)
	return u
}

func TestRedistributeSlots_AllAvailable(t *testing.T) {
	got := redistributeSlots([]bucketRequest{
		{want: 40, available: 100},
		{want: 30, available: 100},
		{want: 30, available: 100},
	})
	if got[0] != 40 || got[1] != 30 || got[2] != 30 {
		t.Errorf("got %v, want [40, 30, 30]", got)
	}
}

func TestRedistributeSlots_ColdStart(t *testing.T) {
	// Both signal buckets empty; all 100 slots roll into random.
	got := redistributeSlots([]bucketRequest{
		{want: 40, available: 0},
		{want: 30, available: 0},
		{want: 30, available: 200},
	})
	if got[0] != 0 || got[1] != 0 {
		t.Errorf("dormant/cross-user should be 0; got %v", got)
	}
	if got[2] != 100 {
		t.Errorf("random = %d, want 100 (cold start fills from random)", got[2])
	}
}

func TestRedistributeSlots_SingleUser(t *testing.T) {
	// Cross-user empty; 30 slots split 15/15 between dormant + random.
	got := redistributeSlots([]bucketRequest{
		{want: 40, available: 100},
		{want: 30, available: 0},
		{want: 30, available: 100},
	})
	if got[1] != 0 {
		t.Errorf("cross-user = %d, want 0", got[1])
	}
	// dormant + random = 40+15 + 30+15 = 100; order of distribution
	// can put the +1 on either side if the deficit was odd, but 30
	// is even so 15/15.
	if got[0] != 55 || got[2] != 45 {
		t.Errorf("got %v, want [55, 0, 45]", got)
	}
}

func TestRedistributeSlots_PartialDormant(t *testing.T) {
	// Dormant returns 25 of 40; deficit = 15, splits 7+8 across peers.
	got := redistributeSlots([]bucketRequest{
		{want: 40, available: 25},
		{want: 30, available: 100},
		{want: 30, available: 100},
	})
	if got[0] != 25 {
		t.Errorf("dormant = %d, want 25 (capped at available)", got[0])
	}
	sum := got[0] + got[1] + got[2]
	if sum != 100 {
		t.Errorf("total = %d, want 100", sum)
	}
	// got[1] and got[2] should each be 30 + (7 or 8).
	if got[1] < 37 || got[1] > 38 {
		t.Errorf("cross-user = %d, want 37 or 38", got[1])
	}
	if got[2] < 37 || got[2] > 38 {
		t.Errorf("random = %d, want 37 or 38", got[2])
	}
}

func TestRedistributeSlots_TotalLibraryEmpty(t *testing.T) {
	// All buckets empty (degenerate library).
	got := redistributeSlots([]bucketRequest{
		{want: 40, available: 0},
		{want: 30, available: 0},
		{want: 30, available: 0},
	})
	if got[0] != 0 || got[1] != 0 || got[2] != 0 {
		t.Errorf("got %v, want [0, 0, 0]", got)
	}
}

func TestCapByAlbumAndArtist_AlbumCap(t *testing.T) {
	rows := []discoverTrack{
		{ID: uuidN(1), AlbumID: uuidN(10), ArtistID: uuidN(100)},
		{ID: uuidN(2), AlbumID: uuidN(10), ArtistID: uuidN(101)},
		{ID: uuidN(3), AlbumID: uuidN(10), ArtistID: uuidN(102)}, // 3rd from album 10 → drop
		{ID: uuidN(4), AlbumID: uuidN(11), ArtistID: uuidN(103)},
	}
	got := capByAlbumAndArtist(rows)
	if len(got) != 3 {
		t.Errorf("len = %d, want 3 (album cap drops the 3rd from album 10)", len(got))
	}
}

func TestCapByAlbumAndArtist_ArtistCap(t *testing.T) {
	rows := []discoverTrack{
		{ID: uuidN(1), AlbumID: uuidN(10), ArtistID: uuidN(100)},
		{ID: uuidN(2), AlbumID: uuidN(11), ArtistID: uuidN(100)},
		{ID: uuidN(3), AlbumID: uuidN(12), ArtistID: uuidN(100)},
		{ID: uuidN(4), AlbumID: uuidN(13), ArtistID: uuidN(100)}, // 4th by artist → drop
		{ID: uuidN(5), AlbumID: uuidN(14), ArtistID: uuidN(101)},
	}
	got := capByAlbumAndArtist(rows)
	if len(got) != 4 {
		t.Errorf("len = %d, want 4 (artist cap drops the 4th by artist 100)", len(got))
	}
}

func TestInterleaveBuckets_RoundRobin(t *testing.T) {
	a := []discoverTrack{{ID: uuidN(1)}, {ID: uuidN(2)}}
	b := []discoverTrack{{ID: uuidN(10)}, {ID: uuidN(20)}}
	c := []discoverTrack{{ID: uuidN(100)}}
	got := interleaveBuckets(a, b, c)
	if len(got) != 5 {
		t.Fatalf("len = %d, want 5", len(got))
	}
	// Expected order: a[0], b[0], c[0], a[1], b[1].
	wantOrder := []byte{1, 10, 100, 2, 20}
	for i, w := range wantOrder {
		if got[i].ID.Bytes[15] != w {
			t.Errorf("got[%d].ID = %d, want %d", i, got[i].ID.Bytes[15], w)
		}
	}
}

func TestInterleaveBuckets_DedupsAcrossBuckets(t *testing.T) {
	// Single-user server scenario: crossUser bucket empty, dormant +
	// random share tracks. Without dedup, shared tracks land at
	// adjacent interleaved positions — the duplication users reported
	// on the Discover playlist in v2026.05.13.0.
	dormant := []discoverTrack{{ID: uuidN(1)}, {ID: uuidN(2)}, {ID: uuidN(3)}}
	crossUser := []discoverTrack{} // empty bucket, single-user server
	random := []discoverTrack{{ID: uuidN(1)}, {ID: uuidN(2)}, {ID: uuidN(4)}}
	got := interleaveBuckets(dormant, crossUser, random)

	// Tracks 1 and 2 appear in both dormant and random — must be
	// emitted once each (from dormant, the earlier bucket). Track 3
	// is dormant-only, track 4 is random-only.
	if len(got) != 4 {
		t.Fatalf("len = %d, want 4 (3 unique from dormant + 1 unique from random)", len(got))
	}
	wantOrder := []byte{1, 2, 3, 4}
	for i, w := range wantOrder {
		if got[i].ID.Bytes[15] != w {
			t.Errorf("got[%d].ID = %d, want %d", i, got[i].ID.Bytes[15], w)
		}
	}
}