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
}