package dx

import (
	"crypto/md5"
	"encoding/hex"
	"sort"
	"strings"
	"time"
)

const (
	// DefaultBaseURL 电信API基础地址
	DefaultBaseURL = "https://cmp-api.ctwing.cn:20164"
)

// GetTimestampGMT 返回 GMT 时区的 yyyyMMddHHmmss 格式时间戳
func GetTimestampGMT() string {
	return time.Now().UTC().Format("20060102150405")
}

// OrderParams 将 URL params 按 key 字典序排序
func OrderParams(params string) (string, error) {
	if params == "" {
		return "", nil
	}
	kvs := strings.Split(params, "&")
	m := make(map[string]string, len(kvs))
	for _, kv := range kvs {
		idx := strings.Index(kv, "=")
		if idx < 0 {
			continue
		}
		m[kv[:idx]] = kv[idx+1:]
	}
	keys := make([]string, 0, len(m))
	for k := range m {
		keys = append(keys, k)
	}
	sort.Strings(keys)
	var parts []string
	for _, k := range keys {
		parts = append(parts, k+"="+m[k])
	}
	return strings.Join(parts, "&"), nil
}

// SignMD5 对 reqStr 做 MD5 加密，返回小写十六进制字符串
func SignMD5(reqStr string) string {
	h := md5.Sum([]byte(reqStr))
	return strings.ToLower(hex.EncodeToString(h[:]))
}

// BuildSign 构造签名：params + body + secretKey + timestamp → MD5 → hex
func BuildSign(params, body, secretKey, timestamp string) (string, error) {
	ordered, err := OrderParams(params)
	if err != nil {
		return "", err
	}
	reqStr := ordered + body + secretKey + timestamp
	md5Str := SignMD5(reqStr)
	return hex.EncodeToString([]byte(md5Str)), nil
}

// BuildSignV3 follows the V3 Java sample: encode the lowercase MD5 digest
// string as hex a second time, then uppercase that outer encoding.
func BuildSignV3(params, body, secretKey, timestamp string) (string, error) {
	sign, err := BuildSign(params, body, secretKey, timestamp)
	return strings.ToUpper(sign), err
}