package main

import (
	"encoding/json"
	"errors"
	"io"
	"net/http"

	"git.k6n.net/mats/go-cart-actor/pkg/promotions"
)

// newPromotionEvaluateHandler serves POST /promotions/evaluate: it takes a
// (possibly partial) evaluation context and returns the totals plus the
// applied/pending promotion effects, without creating or mutating a real cart.
// An empty body is treated as an empty context (evaluates against no items).
func newPromotionEvaluateHandler(store *promotions.Store, svc *promotions.PromotionService) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		var req promotions.EvaluateRequest
		if err := json.NewDecoder(r.Body).Decode(&req); err != nil && !errors.Is(err, io.EOF) {
			http.Error(w, "invalid JSON body: "+err.Error(), http.StatusBadRequest)
			return
		}
		resp := svc.Evaluate(store.Snapshot(), req)
		w.Header().Set("Content-Type", "application/json")
		if err := json.NewEncoder(w).Encode(resp); err != nil {
			http.Error(w, err.Error(), http.StatusInternalServerError)
		}
	}
}