changes with app product stock

services/productVisibility.go

@@ -0,0 +1,53 @@
+package services
+
+import "nearle/models"
+
+// InStockOnly drops the products an outlet cannot actually sell.
+//
+// Being on a shelf is not the same as being in stock. Suriya Store's Peelamedu
+// branch listed three products in the customer app of which exactly one had any
+// stock, so a shopper could add a chocolate bar to their basket and order
+// something the shop did not have. The rule the business wants is the simple
+// one: if we have the stock, it can be ordered — otherwise it is not on offer.
+//
+// ── Why here and not in the SQL ──────────────────────────────────────────────
+//
+// The obvious implementation is another correlated subquery in GetProducts'
+// WHERE clause. This is better for a reason that outlives the convenience:
+// `Productstock` is the number the app DISPLAYS, computed by that query as the
+// live SUM(in)-SUM(out) balance. Filtering on the same value that is shown makes
+// it impossible for the two to disagree. A second copy of the balance
+// expression in a WHERE clause is a copy that can drift from the one in the
+// SELECT, and the failure it produces — a product listed as "3 in stock" that
+// the filter considers empty, or worse the reverse — is very hard to see.
+//
+// It also filters on the ledger rather than productlocations.status. That flag
+// is derived and admits drift: SyncProductLocationStatus repairs it on the next
+// ledger entry, so between an order and that entry it can still read
+// "available" for an empty shelf. The ledger cannot drift from itself.
+//
+// ── The locationID guard ─────────────────────────────────────────────────────
+//
+// Not defensive padding. GetProducts computes the stock balance scoped to
+// params.LocationID, and with no outlet the subquery matches nothing, so EVERY
+// product comes back with Productstock 0. Filtering that would turn an unscoped
+// browse into an empty catalogue rather than an unfiltered one.
+//
+// The console is deliberately unaffected: its inventory screens read
+// GetLocationProducts, a different query, and they must keep showing the empty
+// lines — restocking them is the entire point of that screen.
+func InStockOnly(products []models.Products, locationID int) []models.Products {
+	if locationID <= 0 {
+		return products
+	}
+
+	// Rebuilt rather than filtered in place: the caller's slice is the
+	// repository's own result and nothing here should be writing through it.
+	inStock := make([]models.Products, 0, len(products))
+	for _, p := range products {
+		if p.Productstock > 0 {
+			inStock = append(inStock, p)
+		}
+	}
+	return inStock
+}