package quote

import (
	"context"
	"errors"
	"fmt"
	"math"
	"net/http"
	"strconv"
)

func Total(unit int64, qty int) (int64, error) {
	if qty <= 0 || qty > 100 || unit < 0 {
		return 0, errors.New("invalid quantity or price")
	}
	if unit > math.MaxInt64/int64(qty) {
		return 0, errors.New("total overflow")
	}
	return unit * int64(qty), nil
}

type Prices interface {
	UnitPrice(context.Context, string) (int64, error)
}
type Service struct{ prices Prices }

func NewService(p Prices) *Service { return &Service{prices: p} }
func (s *Service) Quote(ctx context.Context, sku string, qty int) (int64, error) {
	unit, err := s.prices.UnitPrice(ctx, sku)
	if err != nil {
		return 0, fmt.Errorf("lookup price: %w", err)
	}
	return Total(unit, qty)
}
func Handler(s *Service) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		qty, err := strconv.Atoi(r.URL.Query().Get("qty"))
		if err != nil {
			http.Error(w, "invalid quantity", http.StatusBadRequest)
			return
		}
		total, err := s.Quote(r.Context(), r.URL.Query().Get("sku"), qty)
		if err != nil {
			http.Error(w, "quote failed", http.StatusBadRequest)
			return
		}
		fmt.Fprintf(w, "total=%d\n", total)
	})
}