package middleware

import (
	"bytes"
	"crypto/hmac"
	"crypto/sha256"
	"encoding/hex"
	"io"
	"strconv"
	"strings"
	"sync"
	"time"

	"affiliate_dash/internal/pkg/response"

	"github.com/gin-gonic/gin"
)

// OpenAuthConfig 开放接口鉴权配置
type OpenAuthConfig struct {
	APIKey    string
	APISecret string
	// 允许的时间偏差（秒），默认 300
	SkewSeconds int64
}

// nonce 防重放（进程内，重启清空；生产可换 Redis）
type nonceStore struct {
	mu   sync.Mutex
	data map[string]int64 // nonce -> expire unix
}

func newNonceStore() *nonceStore {
	return &nonceStore{data: make(map[string]int64)}
}

func (s *nonceStore) seen(nonce string, now, ttl int64) bool {
	s.mu.Lock()
	defer s.mu.Unlock()
	// 清理过期
	for k, exp := range s.data {
		if exp < now {
			delete(s.data, k)
		}
	}
	if exp, ok := s.data[nonce]; ok && exp >= now {
		return true
	}
	s.data[nonce] = now + ttl
	return false
}

// OpenAuth 校验 X-Api-Key + 时间戳 + nonce + HMAC-SHA256 签名
//
// 待签名字符串（UTF-8，\n 换行）：
//
//	{apiKey}\n{timestamp}\n{nonce}\n{METHOD}\n{path}\n{body}
//
// path 为 URL.Path（不含 query），METHOD 大写；GET 时 body 为空字符串。
// sign = hex(hmac_sha256(apiSecret, stringToSign))，小写十六进制。
func OpenAuth(cfg OpenAuthConfig) gin.HandlerFunc {
	if cfg.SkewSeconds <= 0 {
		cfg.SkewSeconds = 300
	}
	store := newNonceStore()

	return func(c *gin.Context) {
		if cfg.APIKey == "" || cfg.APISecret == "" {
			response.ServerError(c, "服务端未配置 OPEN_API_KEY / OPEN_API_SECRET")
			c.Abort()
			return
		}

		apiKey := c.GetHeader("X-Api-Key")
		timestamp := c.GetHeader("X-Timestamp")
		nonce := c.GetHeader("X-Nonce")
		sign := c.GetHeader("X-Sign")

		if apiKey == "" || timestamp == "" || nonce == "" || sign == "" {
			response.Unauthorized(c, "缺少鉴权头：需要 X-Api-Key、X-Timestamp、X-Nonce、X-Sign")
			c.Abort()
			return
		}
		if apiKey != cfg.APIKey {
			response.Unauthorized(c, "无效的 API Key")
			c.Abort()
			return
		}
		if len(nonce) < 8 || len(nonce) > 64 {
			response.Unauthorized(c, "X-Nonce 长度需在 8~64 之间")
			c.Abort()
			return
		}

		ts, err := strconv.ParseInt(timestamp, 10, 64)
		if err != nil {
			response.Unauthorized(c, "X-Timestamp 格式错误，需为 Unix 秒级时间戳")
			c.Abort()
			return
		}
		now := time.Now().Unix()
		if abs64(now-ts) > cfg.SkewSeconds {
			response.Unauthorized(c, "请求已过期或时间偏差过大")
			c.Abort()
			return
		}

		// 防重放：同一 nonce 在时间窗口内只能用一次
		if store.seen(apiKey+":"+nonce, now, cfg.SkewSeconds) {
			response.Unauthorized(c, "重复的 X-Nonce（请勿重放请求）")
			c.Abort()
			return
		}

		bodyBytes, err := io.ReadAll(c.Request.Body)
		if err != nil {
			response.BadRequest(c, "读取请求体失败")
			c.Abort()
			return
		}
		c.Request.Body = io.NopCloser(bytes.NewBuffer(bodyBytes))

		method := strings.ToUpper(c.Request.Method)
		path := c.Request.URL.Path
		body := string(bodyBytes)

		stringToSign := strings.Join([]string{
			apiKey,
			timestamp,
			nonce,
			method,
			path,
			body,
		}, "\n")

		expected := hmacSHA256Hex(cfg.APISecret, stringToSign)
		if !hmac.Equal([]byte(strings.ToLower(sign)), []byte(expected)) {
			response.Unauthorized(c, "签名校验失败")
			c.Abort()
			return
		}

		c.Next()
	}
}

func hmacSHA256Hex(secret, content string) string {
	mac := hmac.New(sha256.New, []byte(secret))
	_, _ = mac.Write([]byte(content))
	return hex.EncodeToString(mac.Sum(nil))
}

func abs64(v int64) int64 {
	if v < 0 {
		return -v
	}
	return v
}

// BuildOpenSign 供测试或内部生成签名（与 OpenAuth 规则一致）
func BuildOpenSign(apiKey, apiSecret, timestamp, nonce, method, path, body string) string {
	stringToSign := strings.Join([]string{
		apiKey,
		timestamp,
		nonce,
		strings.ToUpper(method),
		path,
		body,
	}, "\n")
	return hmacSHA256Hex(apiSecret, stringToSign)
}