package fadada

import (
	"crypto/hmac"
	"crypto/sha256"
	"encoding/hex"
	"sort"
	"strings"
)

const (
	signTypeHMACSHA256 = "HMAC-SHA256"
	apiSubVersion      = "5.1"
)

// SignByMap 法大大 HMAC-SHA256 签名（与官方 SDK 算法一致）
// 1) 对 map key 字典序排序，拼接 key=value&...（跳过空值）
// 2) signText = hex(SHA256(signContent))
// 3) signKey  = HMAC-SHA256(timestamp, appSecret) 原始字节
// 4) signature = lowercase(hex(HMAC-SHA256(signText, signKey)))
func SignByMap(headMap map[string]string, timestamp, appSecret string) string {
	signContent := sortMapForSign(headMap)
	signText := sha256Hex(signContent)
	secretSigning := hmacSHA256Bytes(timestamp, []byte(appSecret))
	return strings.ToLower(hmacSHA256Hex(signText, secretSigning))
}

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

	parts := make([]string, 0, len(keys))
	for _, k := range keys {
		if v := headMap[k]; v != "" {
			parts = append(parts, k+"="+v)
		}
	}
	return strings.Join(parts, "&")
}

func sha256Hex(src string) string {
	sum := sha256.Sum256([]byte(src))
	return hex.EncodeToString(sum[:])
}

func hmacSHA256Bytes(data string, secret []byte) []byte {
	h := hmac.New(sha256.New, secret)
	h.Write([]byte(data))
	return h.Sum(nil)
}

func hmacSHA256Hex(data string, secret []byte) string {
	return hex.EncodeToString(hmacSHA256Bytes(data, secret))
}