67 lines
2.8 KiB
Go
67 lines
2.8 KiB
Go
// Package inventory is the platform's shared inventory seam: the cross-module
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// vocabulary for stock *levels*. It deliberately carries no quantities — exact
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// stock is queried synchronously from the inventory service at decision points
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// (PDP, add-to-cart, checkout reserve), and only coarse level crossings travel
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// over the bus. Putting exact quantity on the bus spams it and ships a number
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// that is stale the moment it is published; a level crossing is the only
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// inventory signal other modules receive. See docs/inventory-shape.md.
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//
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// Like platform/catalog, this package holds only the wire value types plus the
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// single classification function, so the producer and every consumer agree on
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// the cutoffs. It imports only the stdlib — never an app module, never a
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// transport library.
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package inventory
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import "encoding/json"
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// Level is the coarse, bus-safe stock state. Consumers map a Level to a display
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// hint / availability flag; they never see (or need) the exact quantity.
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type Level string
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const (
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LevelNone Level = "none" // nothing available to sell
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LevelLow Level = "low" // at or below the low watermark, but still > 0
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LevelHigh Level = "high" // comfortably above the low watermark
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)
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// LevelFor classifies an exact on-hand quantity into a Level given the low
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// watermark. It is the single source of the cutoffs: the producer computes the
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// emitted level with it, and any consumer that needs to reclassify a quantity
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// (e.g. after a synchronous exact query) uses the same function so the two can
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// never disagree. qty <= 0 → none; 0 < qty <= low → low; qty > low → high.
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func LevelFor(qty, lowWatermark int64) Level {
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switch {
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case qty <= 0:
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return LevelNone
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case qty <= lowWatermark:
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return LevelLow
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default:
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return LevelHigh
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}
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}
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// InStock reports whether the level means the SKU can be sold (any level other
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// than none) — a convenience for consumers that only care about the boolean.
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func (l Level) InStock() bool { return l != LevelNone }
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// LevelChanged is the payload of an event.InventoryLevelChanged envelope: the
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// SKU + location whose level crossed a threshold, and the new level — never a
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// quantity. The envelope's Subject duplicates SKU; Meta["country"] carries the
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// tenant/country for consumer routing (matching the catalog wire convention).
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type LevelChanged struct {
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SKU string `json:"sku"`
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Location string `json:"location"`
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Level Level `json:"level"`
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}
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// Encode serialises the payload for event.Event.Payload. Kept here so producer
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// and consumers share the exact wire shape; any future renaming lands here.
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func (c LevelChanged) Encode() ([]byte, error) { return json.Marshal(c) }
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// Decode parses an InventoryLevelChanged payload — the consumer side of Encode.
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func Decode(raw []byte) (LevelChanged, error) {
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var c LevelChanged
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err := json.Unmarshal(raw, &c)
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return c, err
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}
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