uniform

cmd/cart/projection.go

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+package main
+
+import (
+	"git.k6n.net/mats/platform/catalog"
+)
+
+// catalogProjectionCache is the cart's per-pod, cold-start-ready catalog
+// projection cache, backed by platform/catalog.ProjectionStore. It consumes the
+// catalog.projection_published wire — a full snapshot (begin/chunk/end, framed by
+// epoch) plus incremental deltas — into its OWN local .bin and serves catalog
+// facts by SKU (price, tax_class, inventory_tracked, image, …) at add-to-cart /
+// checkout-reserve decisions. Stock is NOT cached — queried synchronously from
+// inventory per docs/inventory-shape.md.
+//
+// Clustering: the cart runs N replicas. Each pod has its OWN exclusive bus queue
+// (rabbit.ListenToPattern declares an exclusive server-named queue, so every pod
+// receives the full stream) and its OWN pod-local .bin. It's a replicated read
+// cache — no leader, no shared volume; N pods writing one file would corrupt it.
+// See docs/catalog-projection.md.
+//
+// The cart stores the full catalog.Projection (identity transform): its
+// add-to-cart overlay (projection_overlay.go) consumes nearly every field, so
+// there's nothing to subset. Deletes ride as tombstones in the store's overlay
+// (IsDeleted) so a removed SKU isn't re-fetched before the next snapshot folds
+// the delete into the base. Cold-grace: an SKU not yet in the base/overlay
+// resolves via the existing PRODUCT_BASE_URL HTTP fetch + overlay.
+type catalogProjectionCache struct {
+	store *catalog.ProjectionStore[catalog.Projection]
+}
+
+// identityProjection is the cart's mandatory transform — it stores the full
+// Projection because the overlay uses almost all of it.
+func identityProjection(p catalog.Projection) catalog.Projection { return p }
+
+// newCatalogProjectionCache opens the per-pod store under dir. dir MUST be
+// pod-local (container fs / an emptyDir in k8s) — never a shared volume.
+func newCatalogProjectionCache(dir string) (*catalogProjectionCache, error) {
+	s, err := catalog.NewProjectionStore(dir, "cart-projection.bin", identityProjection, nil)
+	if err != nil {
+		return nil, err
+	}
+	return &catalogProjectionCache{store: s}, nil
+}
+
+// HandleFrame feeds one catalog.projection_published event (snapshot frame or
+// delta) into the store; framing/epoch ordering live in platform/catalog.
+func (c *catalogProjectionCache) HandleFrame(meta map[string]string, payload []byte) error {
+	return c.store.HandleFrame(meta, payload)
+}
+
+func (c *catalogProjectionCache) Get(sku string) (catalog.Projection, bool) { return c.store.Get(sku) }
+
+// IsDeleted reports whether the bus has explicitly deleted sku (overlay
+// tombstone) — call sites skip the HTTP fallback for it.
+func (c *catalogProjectionCache) IsDeleted(sku string) bool { return c.store.IsDeleted(sku) }
+
+// Len reports cached entries (base + overlay) — debug/log gauge only.
+func (c *catalogProjectionCache) Len() int {
+	_, base, overlay := c.store.Stats()
+	return base + overlay
+}