mcp

pkg/promotions/mcp/public.go

@@ -0,0 +1,173 @@
+package mcp
+
+import (
+	"encoding/json"
+	"fmt"
+	"time"
+
+	"git.k6n.net/mats/go-cart-actor/pkg/promotions"
+)
+
+// NewPublic builds an MCP server exposing only the read-only promotion tools:
+// list_promotions, get_promotion, preview_cart_discount, and evaluate_promotion.
+// This is mounted on the public-facing endpoint (no auth needed since all tools
+// are safe to expose).
+func NewPublic(store *promotions.Store, eval *promotions.PromotionService) *Server {
+	if eval == nil {
+		eval = promotions.NewPromotionService(nil)
+	}
+	s := &Server{store: store, eval: eval}
+	s.tools = s.buildPublicTools()
+	return s
+}
+
+func (s *Server) buildPublicTools() []tool {
+	return []tool{
+		{
+			Name:        "list_promotions",
+			Description: "List all promotion rules the cart engine evaluates, optionally filtered by status (active|inactive|scheduled|expired).",
+			InputSchema: object(props{
+				"status": str("optional status filter: active|inactive|scheduled|expired"),
+			}, nil),
+			invoke: func(args json.RawMessage) (any, error) {
+				var a struct {
+					Status string `json:"status"`
+				}
+				if err := decode(args, &a); err != nil {
+					return nil, err
+				}
+				rules := s.store.List()
+				if a.Status != "" {
+					filtered := rules[:0:0]
+					for _, r := range rules {
+						if string(r.Status) == a.Status {
+							filtered = append(filtered, r)
+						}
+					}
+					rules = filtered
+				}
+				return map[string]any{"promotions": rules, "count": len(rules)}, nil
+			},
+		},
+		{
+			Name:        "get_promotion",
+			Description: "Fetch a single promotion rule by id.",
+			InputSchema: object(props{"id": str("the promotion id")}, []string{"id"}),
+			invoke: func(args json.RawMessage) (any, error) {
+				var a struct {
+					ID string `json:"id"`
+				}
+				if err := decode(args, &a); err != nil {
+					return nil, err
+				}
+				r, ok := s.store.Get(a.ID)
+				if !ok {
+					return nil, fmt.Errorf("promotion %q not found", a.ID)
+				}
+				return r, nil
+			},
+		},
+		{
+			Name: "preview_cart_discount",
+			Description: "Evaluate the current active promotions against a hypothetical cart total and report the " +
+				"matched discount. cartTotalIncVat is in öre incl. VAT (e.g. 5 000 000 = 50 000 kr). Useful for " +
+				"verifying Volymrabatt tiers without touching a real cart.",
+			InputSchema: object(props{
+				"cartTotalIncVat": integer("cart total incl. VAT, in öre"),
+				"itemQuantity":    integer("optional total item quantity"),
+				"customerSegment": str("optional customer segment"),
+			}, []string{"cartTotalIncVat"}),
+			invoke: func(args json.RawMessage) (any, error) {
+				var a struct {
+					CartTotalIncVat int64  `json:"cartTotalIncVat"`
+					ItemQuantity    int    `json:"itemQuantity"`
+					CustomerSegment string `json:"customerSegment"`
+				}
+				if err := decode(args, &a); err != nil {
+					return nil, err
+				}
+				g := syntheticCart(a.CartTotalIncVat, a.ItemQuantity)
+				opts := []promotions.ContextOption{promotions.WithNow(time.Now())}
+				if a.CustomerSegment != "" {
+					opts = append(opts, promotions.WithCustomerSegment(a.CustomerSegment))
+				}
+				ctx := promotions.NewContextFromCart(g, opts...)
+				results, actions := s.eval.EvaluateAll(s.store.Snapshot(), ctx)
+				s.eval.ApplyResults(g, results, ctx)
+				return map[string]any{
+					"subtotalIncVat":    a.CartTotalIncVat,
+					"discountIncVat":    g.TotalDiscount.IncVat,
+					"netIncVat":         g.TotalPrice.IncVat,
+					"matchedActions":    actions,
+					"appliedPromotions": g.AppliedPromotions,
+				}, nil
+			},
+		},
+		{
+			Name: "evaluate_promotion",
+			Description: "Evaluate promotions against a hypothetical cart and return the full evaluation result: " +
+				"which promotions match, what discount they apply, and any pending next-tier nudges (\"spend X more for Y%\"). " +
+				"When promotionId is set, only that specific promotion is evaluated (useful for testing a new rule). " +
+				"When omitted, all active promotions are evaluated. cartTotalIncVat is in öre incl. VAT.",
+			InputSchema: object(props{
+				"cartTotalIncVat": integer("cart total incl. VAT, in öre"),
+				"promotionId":     str("optional: evaluate only this promotion (by id)"),
+				"itemQuantity":    integer("optional total item quantity"),
+				"customerSegment": str("optional customer segment"),
+			}, []string{"cartTotalIncVat"}),
+			invoke: func(args json.RawMessage) (any, error) {
+				var a struct {
+					CartTotalIncVat int64  `json:"cartTotalIncVat"`
+					PromotionId     string `json:"promotionId"`
+					ItemQuantity    int    `json:"itemQuantity"`
+					CustomerSegment string `json:"customerSegment"`
+				}
+				if err := decode(args, &a); err != nil {
+					return nil, err
+				}
+
+				rules := s.store.Snapshot()
+				if a.PromotionId != "" {
+					filtered := rules[:0:0]
+					for _, r := range rules {
+						if r.ID == a.PromotionId {
+							filtered = append(filtered, r)
+							break
+						}
+					}
+					if len(filtered) == 0 {
+						return nil, fmt.Errorf("promotion %q not found", a.PromotionId)
+					}
+					rules = filtered
+				}
+
+				g := syntheticCart(a.CartTotalIncVat, a.ItemQuantity)
+				opts := []promotions.ContextOption{promotions.WithNow(time.Now())}
+				if a.CustomerSegment != "" {
+					opts = append(opts, promotions.WithCustomerSegment(a.CustomerSegment))
+				}
+				ctx := promotions.NewContextFromCart(g, opts...)
+				results, actions := s.eval.EvaluateAll(rules, ctx)
+				evalResults := make([]map[string]any, 0, len(results))
+				for _, r := range results {
+					evalResults = append(evalResults, map[string]any{
+						"ruleId":       r.Rule.ID,
+						"name":         r.Rule.Name,
+						"applicable":   r.Applicable,
+						"failedReason": r.FailedReason,
+						"matchedActions": r.MatchedActions,
+					})
+				}
+				s.eval.ApplyResults(g, results, ctx)
+				return map[string]any{
+					"subtotalIncVat":    a.CartTotalIncVat,
+					"discountIncVat":    g.TotalDiscount.IncVat,
+					"netIncVat":         g.TotalPrice.IncVat,
+					"matchedActions":    actions,
+					"appliedPromotions": g.AppliedPromotions,
+					"evaluationResults": evalResults,
+				}, nil
+			},
+		},
+	}
+}