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