package main

import (
	"bytes"
	"crypto/md5"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"sort"
	"strings"
)

const (
	appKey = "DD3BZ-4643M-RJ76E-6WGEY-JZ4KO-2OBIG"
	appSK  = "Px6Ig8s6ar0vFdnJXgcYoFvy4w3Z8wfr"
	apiURL = "https://apis.map.qq.com/ws/distance/v1/matrix"
)

// 请求参数结构体
type RequestParams struct {
	Key  string `json:"key"`
	From string `json:"from"`
	To   string `json:"to"`
	Mode string `json:"mode"`
}

func main() {
	// 1. 原始参数
	params := RequestParams{
		Key:  appKey,
		From: "39.940552,116.344101", // 北京展览馆
		To:   "39.916585,116.319596", // 中塔公园
		Mode: "driving",
	}

	// 2. 取得结构体字段的排序后 kv 列表
	kv, err := toSortedKV(params)
	if err != nil {
		panic(err)
	}

	// 3. 拼成 querystring（不含 sig），再追加 SK
	tosign := "/ws/distance/v1/matrix?" + kv + appSK
	fmt.Println("request query:", tosign)
	// 4. 计算 MD5（小写）
	sig := fmt.Sprintf("%x", md5.Sum([]byte(tosign)))

	// 5. 组装最终 URL
	finalURL := apiURL + "?sig=" + sig
	fmt.Println("request url:", finalURL)

	// 6. 发送 GET 请求
	// 4. 发送 POST JSON
	jsonBytes, _ := json.Marshal(params)
	resp, err := http.Post(finalURL, "application/json", bytes.NewReader(jsonBytes))
	defer resp.Body.Close()

	body, _ := io.ReadAll(resp.Body)
	fmt.Printf("status=%d\nbody=%s\n", resp.StatusCode, body)
}

// 按字段名升序拼成 key=value
func toSortedKV(v interface{}) (string, error) {
	// 结构体转 map
	var m map[string]interface{}
	b, _ := json.Marshal(v)
	if err := json.Unmarshal(b, &m); err != nil {
		return "", err
	}

	keys := make([]string, 0, len(m))
	for k := range m {
		keys = append(keys, k)
	}
	sort.Strings(keys)

	var sb strings.Builder
	for i, k := range keys {
		// 值 → 最短 JSON → 去首尾双引号
		valBytes, _ := json.Marshal(m[k])
		valStr := string(valBytes)
		if len(valStr) >= 2 && valStr[0] == '"' && valStr[len(valStr)-1] == '"' {
			valStr = valStr[1 : len(valStr)-1]
		}
		if i > 0 {
			sb.WriteByte('&')
		}
		sb.WriteString(k)
		sb.WriteByte('=')
		sb.WriteString(valStr)
	}
	return sb.String(), nil
}