package main

import (
	messages "git.k6n.net/mats/go-cart-actor/proto/cart"
	"git.k6n.net/mats/platform/catalog"
)

// taxClassToBp maps the canonical TaxClass string identifiers published on
// catalog.Projection to basis-points-of-a-percent (rate × 100) — the single
// platform-wide rate scale used by AddItem.Tax (int32 basis points), the
// mutation registry, and the tax.Provider Compute formula.
//
// Values reflect the standard tariff names used by the Nordic configuration.
// Per-country / per-tenant numeric resolution (e.g. Finland 25.5%, Ireland
// 13.5%) is delegated to platform/tax and is a follow-up: this static map
// gets the common case right (2500 / 1200 / 600 / 0) and lets the cache path
// ship while the platform/tax lookup is wired into the cart pool server.
var taxClassToBp = map[string]int{
	"standard":  2500,
	"reduced":   1200, // common reduced rate (e.g. SE/NO food)
	"lowered":   600,  // super-reduced
	"zero":      0,    // zero-rated (export, healthcare, ...)
	"exempt":    0,    // similarly untaxed, separate nominal class
}

// resolveTaxBp returns the basis-point rate for a TaxClass string, falling
// back to platform "standard" (25%) when the class is unrecognised. The
// default matches the grain's existing behaviour (AddItem falls back to 2500
// when m.Tax == 0 — see pkg/cart/mutation_add_item.go).
func resolveTaxBp(class string) int {
	if bp, ok := taxClassToBp[class]; ok {
		return bp
	}
	return 2500
}

// ApplyProjectionOverlay overlays the cache's authoritative catalog facts onto
// an AddItem message that was just produced by a PRODUCT_BASE_URL HTTP fetch.
//
// Authoritative-from-cache fields (these WIN over the HTTP-fetched value when
// both are present, because the bus is the live stream):
//
//	Price          (bus has post-class-overrides; product service has static)
//	Tax            (TaxClass → bp via resolveTaxBp; only when TaxClass is set —
//	                  an empty TaxClass means the producer didn't classify,
//	                  so we leave the HTTP-fetched rate intact rather than
//	                  quietly swapping in a default 2500 and miscategorising)
//	Title          (canonical, post-trim)
//	Image          (canonical)
//	InventoryTracked (only flips to true; false is the zero value in proto
//	                  and may be unset on the wire, so we don't second-guess)
//	DropShip       (only flips to true; same reasoning)
//
// The HTTP-fetched values remain authoritative for fields the cache does not
// carry: SellerId / SellerName (marketplace split), Stock (per docs/inventory-
// shape.md stock is queried synchronously from inventory, not cached),
// OrgPrice / Discount (not yet on the projection schema), the dynamic
// ExtraJson product data (configurator options — width/height used by
// accessory child-pricing), and the catalog uint32 ItemId (the product
// service's integer id which messages.AddItem.ItemId dedupes on — Projection
// only carries the opaque string ID, so a cache-only build path is blocked
// and the HTTP fetch is preserved).
//
// Tombstoned SKUs (catalog.projection_published with deleted=true) → the
// caller checks idx.IsDeleted(sku) before this helper and short-circuits.
func ApplyProjectionOverlay(msg *messages.AddItem, p catalog.Projection) {
	if msg == nil {
		return
	}
	// Price: positive bus values override HTTP. A zero PriceIncVat is treated
	// as "no value" rather than "free".
	if p.PriceIncVat.Int64() > 0 {
		msg.Price = p.PriceIncVat.Int64()
	}
	// Tax: only override when the bus has classified the SKU. An empty TaxClass
	// means the producer had nothing to say about VAT; the HTTP rate is more
	// trustworthy in that case than a guessed 2500.
	if p.TaxClass != "" {
		msg.Tax = int32(resolveTaxBp(p.TaxClass))
	}
	// Display fields: only override if non-empty so the HTTP-fanned value
	// remains in place when the cache hasn't populated them yet.
	if p.Title != "" {
		msg.Name = p.Title
	}
	if p.Image != "" {
		msg.Image = p.Image
	}
	// Flags: only flip to true (positive boolean signals). A false is the
	// proto-zero value and not worth overriding.
	if p.InventoryTracked {
		msg.InventoryTracked = true
	}
	if p.DropShip {
		msg.DropShip = true
	}
}