feat(artwork): read a single queue row by item

The explain CLI must report whether an item is queued, at what priority and when it
retries; the queue repository could only be drained in eligibility batches, which
cannot see a row that is still backing off.

model/artwork.go

@@ -119,6 +119,8 @@ type ArtworkRepository interface {
 }
 
 type ArtworkQueueRepository interface {
+	// Get returns the pending row for an item, or ErrNotFound when it is not queued.
+	Get(kind Kind, id, imageType string) (*ArtworkQueueItem, error)
 	// Enqueue upserts; an existing row keeps the higher priority and has its retry_at reset.
 	Enqueue(items ...ArtworkQueueItem) error
 	// EnqueuePreservingBackoff upserts like Enqueue but preserves an existing row's retry_at, so a

persistence/artwork_queue_repository.go

@@ -31,6 +31,16 @@ func NewArtworkQueueRepository(ctx context.Context, db dbx.Builder) model.Artwor
 	return r
 }
 
+func (r *artworkQueueRepository) Get(kind model.Kind, id, imageType string) (*model.ArtworkQueueItem, error) {
+	var res model.ArtworkQueueItem
+	err := r.queryOne(Select("*").From(r.tableName).
+		Where(Eq{"item_kind": kind.Prefix(), "item_id": id, "image_type": imageType}), &res)
+	if err != nil {
+		return nil, err
+	}
+	return &res, nil
+}
+
 // Enqueue also resets enqueued_at, so a fresh request does not inherit an old row's spent retry budget.
 func (r *artworkQueueRepository) Enqueue(items ...model.ArtworkQueueItem) error {
 	return r.enqueue(`ON CONFLICT (item_kind, item_id, image_type) DO UPDATE SET

persistence/artwork_queue_repository_test.go

@@ -54,6 +54,22 @@ var _ = Describe("ArtworkQueueRepository", func() {
 		Expect(got[0].ItemID).To(Equal("high"))
 	})
 
+	It("Get returns a queued row, including one still backing off", func() {
+		Expect(repo.Enqueue(item("ar", "g1", model.ArtworkPriorityScan))).To(Succeed())
+		backOff("ar", "g1", time.Now().Add(time.Hour))
+
+		got, err := repo.Get(model.KindArtistArtwork, "g1", model.ImageTypePrimary)
+		Expect(err).ToNot(HaveOccurred())
+		Expect(got.Priority).To(Equal(model.ArtworkPriorityScan))
+		Expect(got.Attempts).To(Equal(1))
+		Expect(got.RetryAt).To(BeTemporally(">", time.Now()))
+	})
+
+	It("Get reports ErrNotFound when the item is not queued", func() {
+		_, err := repo.Get(model.KindArtistArtwork, "nope", model.ImageTypePrimary)
+		Expect(err).To(MatchError(model.ErrNotFound))
+	})
+
 	It("keeps the higher priority on duplicate enqueue", func() {
 		Expect(repo.Enqueue(item("al", "a1", model.ArtworkPriorityBump))).To(Succeed())
 		Expect(repo.Enqueue(item("al", "a1", model.ArtworkPriorityBackfill))).To(Succeed())

tests/mock_artwork_queue_repo.go

@@ -25,6 +25,19 @@ func CreateMockArtworkQueueRepo() *MockArtworkQueueRepo {
 	return &MockArtworkQueueRepo{Data: map[string]model.ArtworkQueueItem{}}
 }
 
+func (m *MockArtworkQueueRepo) Get(kind model.Kind, id, imageType string) (*model.ArtworkQueueItem, error) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	if m.Err != nil {
+		return nil, m.Err
+	}
+	it, ok := m.Data[iaKey(kind.Prefix(), id, imageType)]
+	if !ok {
+		return nil, model.ErrNotFound
+	}
+	return &it, nil
+}
+
 func (m *MockArtworkQueueRepo) Enqueue(items ...model.ArtworkQueueItem) error {
 	m.mu.Lock()
 	defer m.mu.Unlock()