package qcxg

import (
	_ "embed"
	"encoding/json"
	"strings"
	"unicode/utf8"
)

//go:embed data/car_plate.json
var carPlateJSON []byte

var carPlateCityMap map[string]string

func init() {
	carPlateCityMap = make(map[string]string)
	_ = json.Unmarshal(carPlateJSON, &carPlateCityMap)
}

// lookupCityByPlateNo 根据车牌号前缀（省简称+字母）查城市，未匹配返回 "-"
func lookupCityByPlateNo(plateNo string) string {
	prefix := extractPlatePrefix(plateNo)
	if prefix == "" {
		return "-"
	}
	if city, ok := carPlateCityMap[prefix]; ok && city != "" {
		return city
	}
	return "-"
}

// extractPlatePrefix 取车牌前两个字符作为字典键，如 "鲁A12345" -> "鲁A"
func extractPlatePrefix(plateNo string) string {
	plateNo = strings.TrimSpace(plateNo)
	if plateNo == "" {
		return ""
	}
	if utf8.RuneCountInString(plateNo) < 2 {
		return ""
	}
	runes := []rune(plateNo)
	return string(runes[:2])
}