120 lines
4.0 KiB
Go
120 lines
4.0 KiB
Go
package promotions
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import (
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"time"
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"git.k6n.net/mats/go-cart-actor/pkg/cart"
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)
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// ----------------------------
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// Stateless evaluation
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// ----------------------------
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//
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// Evaluate runs the promotion engine against a caller-supplied context instead
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// of a real cart, so a storefront can ask "what would these items get?" without
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// creating or mutating a cart. It builds a synthetic CartGrain from the request,
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// runs the same EvaluateAll + ApplyResults path the live cart uses, and returns
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// the resulting totals plus the applied/pending effect breakdown.
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// EvalItem is one — possibly partial — cart line for a stateless evaluation.
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// Missing fields fall back to sensible defaults (qty 1, 25% VAT) so the engine
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// does the best it can with whatever the caller provides.
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type EvalItem struct {
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Sku string `json:"sku,omitempty"`
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Category string `json:"category,omitempty"`
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Quantity uint16 `json:"qty,omitempty"`
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PriceIncVat int64 `json:"priceIncVat,omitempty"`
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VatRate float32 `json:"vatRate,omitempty"`
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}
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// EvaluateRequest is a stateless promotion-evaluation context. Every field is
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// optional. Items drive the cart total and the item-scoped conditions; when no
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// items are given, CartTotalIncVat synthesises a single line so total-only rules
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// (volume discounts, free-shipping thresholds) can still be previewed.
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type EvaluateRequest struct {
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Items []EvalItem `json:"items,omitempty"`
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CartTotalIncVat int64 `json:"cartTotalIncVat,omitempty"`
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CustomerSegment string `json:"customerSegment,omitempty"`
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CustomerLifetimeValue float64 `json:"customerLifetimeValue,omitempty"`
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OrderCount int `json:"orderCount,omitempty"`
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Now *time.Time `json:"now,omitempty"`
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}
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// EvaluateResponse is the outcome of a stateless evaluation: the totals after
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// promotions and the per-promotion breakdown (applied discounts plus pending
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// "spend X more for ..." nudges).
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type EvaluateResponse struct {
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TotalPrice *cart.Price `json:"totalPrice"`
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TotalDiscount *cart.Price `json:"totalDiscount"`
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AppliedPromotions []cart.AppliedPromotion `json:"appliedPromotions,omitempty"`
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}
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// Evaluate runs rules against a synthetic cart built from req and returns the
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// resulting totals and effects without touching any real cart state.
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func (s *PromotionService) Evaluate(rules []PromotionRule, req EvaluateRequest) EvaluateResponse {
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g := req.toCart()
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g.UpdateTotals()
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ctx := NewContextFromCart(g, req.contextOptions()...)
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results, _ := s.EvaluateAll(rules, ctx)
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s.ApplyResults(g, results, ctx)
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return EvaluateResponse{
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TotalPrice: g.TotalPrice,
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TotalDiscount: g.TotalDiscount,
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AppliedPromotions: g.AppliedPromotions,
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}
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}
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// toCart materialises the request into a throwaway CartGrain.
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func (req EvaluateRequest) toCart() *cart.CartGrain {
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now := time.Now()
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if req.Now != nil {
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now = *req.Now
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}
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g := cart.NewCartGrain(0, now)
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for _, it := range req.Items {
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qty := it.Quantity
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if qty == 0 {
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qty = 1
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}
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vat := it.VatRate
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if vat == 0 {
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vat = 25
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}
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item := &cart.CartItem{
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Sku: it.Sku,
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Quantity: qty,
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Price: *cart.NewPriceFromIncVat(it.PriceIncVat, vat),
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}
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if it.Category != "" {
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item.Meta = &cart.ItemMeta{Category: it.Category}
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}
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g.Items = append(g.Items, item)
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}
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if len(g.Items) == 0 && req.CartTotalIncVat > 0 {
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g.Items = append(g.Items, &cart.CartItem{
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Sku: "synthetic",
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Quantity: 1,
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Price: *cart.NewPriceFromIncVat(req.CartTotalIncVat, 25),
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})
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}
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return g
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}
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// contextOptions maps the optional customer/time fields onto context options.
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func (req EvaluateRequest) contextOptions() []ContextOption {
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var opts []ContextOption
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if req.Now != nil {
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opts = append(opts, WithNow(*req.Now))
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}
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if req.CustomerSegment != "" {
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opts = append(opts, WithCustomerSegment(req.CustomerSegment))
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}
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if req.CustomerLifetimeValue != 0 {
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opts = append(opts, WithCustomerLifetimeValue(req.CustomerLifetimeValue))
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}
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if req.OrderCount != 0 {
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opts = append(opts, WithOrderCount(req.OrderCount))
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}
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return opts
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}
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