package intelligence_finance_v1

import (
	"crypto/hmac"
	"crypto/rand"
	"crypto/sha256"
	"encoding/base64"
	"fmt"
	"math/big"
	"sort"
	"strings"
	"time"
)

// GenerateTimestamp 生成秒级时间戳字符串
func GenerateTimestamp() string {
	return fmt.Sprintf("%d", time.Now().Unix())
}

// GenerateTimestampMillis 生成毫秒级时间戳字符串
func GenerateTimestampMillis() string {
	return fmt.Sprintf("%d", time.Now().UnixMilli())
}

// GenerateNonce 生成指定长度的加密安全随机字符串
// length 建议为 16-32 位
func GenerateNonce(length int) (string, error) {
	const charset = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
	b := make([]byte, length)
	for i := range b {
		num, err := rand.Int(rand.Reader, big.NewInt(int64(len(charset))))
		if err != nil {
			return "", fmt.Errorf("generate nonce: %w", err)
		}
		b[i] = charset[num.Int64()]
	}
	return string(b), nil
}

// HmacSHA256Sign 使用 HmacSHA256 算法对数据进行签名，返回 Base64 编码的签名字符串
// 密钥为 client-secret，签名数据为 timestamp + nonce
func HmacSHA256Sign(secret string, data string) string {
	h := hmac.New(sha256.New, []byte(secret))
	h.Write([]byte(data))
	return base64.StdEncoding.EncodeToString(h.Sum(nil))
}

// HmacSHA256Verify 验证 HmacSHA256 签名
func HmacSHA256Verify(secret string, data string, signature string) bool {
	expected := HmacSHA256Sign(secret, data)
	return hmac.Equal([]byte(expected), []byte(signature))
}

// BuildSignString 按字典序排序拼接参数，格式为 key=value&key2=value2
// 排除空值、sign 和 signature 字段
func BuildSignString(params map[string]string) string {
	keys := make([]string, 0, len(params))
	for k, v := range params {
		if v != "" && k != "sign" && k != "signature" {
			keys = append(keys, k)
		}
	}
	sort.Strings(keys)

	var parts []string
	for _, k := range keys {
		parts = append(parts, fmt.Sprintf("%s=%s", k, params[k]))
	}
	return strings.Join(parts, "&")
}

// BuildSignStringOrdered 按固定顺序拼接参数
func BuildSignStringOrdered(params map[string]string, orderedKeys []string) string {
	var parts []string
	for _, k := range orderedKeys {
		if v, ok := params[k]; ok && v != "" {
			parts = append(parts, fmt.Sprintf("%s=%s", k, v))
		}
	}
	return strings.Join(parts, "&")
}