package service

import (
	"crypto/hmac"
	"crypto/sha256"
	"encoding/hex"
	"fmt"
	"net/http"
	"net/url"
	"strconv"
	"strings"
	"time"

	"affiliate_dash/internal/model"
)

func (s *DeliveryService) authorizeDeliveryLink(order *model.FulfillmentOrder, auth DeliveryLinkAuth) error {
	if order == nil {
		return newDeliveryHTTPError(http.StatusNotFound, "订单不存在")
	}
	if strings.TrimSpace(auth.Sign) == "" {
		return newDeliveryHTTPError(http.StatusForbidden, "链接参数缺失")
	}
	if order.DeliveryLinkRevokedAt != nil {
		return newDeliveryHTTPError(http.StatusForbidden, "发货链接已作废")
	}
	// 订单已取消后链接立即失效，防止已退款订单仍通过链接查看或继续发货。
	if normalizeOrderStatus(order) == model.OrderStatusCancelled {
		return newDeliveryHTTPError(http.StatusForbidden, "订单已取消，发货链接不可用")
	}
	// 从未生成过链接（兼容历史数据：本次改动前生成的有时效链接没有 generated_at 记录）。
	if order.DeliveryLinkGeneratedAt == nil && order.DeliveryLinkExpiresAt == nil {
		return newDeliveryHTTPError(http.StatusForbidden, "发货链接未生成")
	}
	// 永久有效链接（expires_at 为 NULL）：仅校验签名（exp 固定为 0），不检查过期。
	if order.DeliveryLinkExpiresAt == nil {
		expected := s.signDeliveryLink(order.OrderNo, auth.Exp)
		if !hmac.Equal([]byte(strings.ToLower(strings.TrimSpace(auth.Sign))), []byte(expected)) {
			return newDeliveryHTTPError(http.StatusForbidden, "发货链接签名无效")
		}
		return nil
	}
	expiresAt := order.DeliveryLinkExpiresAt.UTC().Truncate(time.Second)
	linkExpires := time.Unix(auth.Exp, 0).UTC()
	if !linkExpires.Equal(expiresAt) {
		return newDeliveryHTTPError(http.StatusForbidden, "发货链接已失效")
	}
	if time.Now().UTC().After(linkExpires) {
		return newDeliveryHTTPError(http.StatusForbidden, "发货链接已过期")
	}
	expected := s.signDeliveryLink(order.OrderNo, auth.Exp)
	if !hmac.Equal([]byte(strings.ToLower(strings.TrimSpace(auth.Sign))), []byte(expected)) {
		return newDeliveryHTTPError(http.StatusForbidden, "发货链接签名无效")
	}
	return nil
}

// buildDeliveryLinkResult 组装链接结果；expiresAt 为 nil 表示永久有效（exp 固定为 0）。
func (s *DeliveryService) buildDeliveryLinkResult(orderNo string, expiresAt *time.Time, requestBaseURL string) *DeliveryLinkResult {
	exp := int64(0)
	if expiresAt != nil {
		exp = expiresAt.UTC().Unix()
	}
	sign := s.signDeliveryLink(orderNo, exp)
	return &DeliveryLinkResult{
		OrderNo:     orderNo,
		DeliveryURL: s.buildDeliveryURL(orderNo, exp, sign, requestBaseURL),
		ExpiresAt:   expiresAt,
		Exp:         exp,
		Sign:        sign,
	}
}

func (s *DeliveryService) buildDeliveryURL(orderNo string, exp int64, sign, requestBaseURL string) string {
	path := fmt.Sprintf("/delivery/%s/%s?exp=%d&sign=%s", url.PathEscape(s.channel), url.PathEscape(orderNo), exp, url.QueryEscape(sign))
	base := strings.TrimRight(s.linkBaseURL, "/")
	if base == "" {
		base = strings.TrimRight(requestBaseURL, "/")
	}
	if base == "" {
		return path
	}
	return base + path
}

func (s *DeliveryService) signDeliveryLink(orderNo string, exp int64) string {
	mac := hmac.New(sha256.New, []byte(s.linkSecret))
	_, _ = mac.Write([]byte(orderNo + "|" + strconv.FormatInt(exp, 10)))
	return hex.EncodeToString(mac.Sum(nil))
}