package service

import (
	"crypto/sha256"
	"encoding/hex"
	"errors"
	"regexp"
	"strings"
	"time"

	"github.com/freefire/jiang13-bbs/model"
	"gorm.io/gorm"
	"gorm.io/gorm/clause"
)

var (
	vidUUIDRe = regexp.MustCompile(`(?i)^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$`)
)

// TelemetryService 轻量页面访问埋点
type TelemetryService struct {
	db *gorm.DB
}

func NewTelemetryService(db *gorm.DB) *TelemetryService {
	return &TelemetryService{db: db}
}

func todayDate() time.Time {
	now := time.Now()
	return time.Date(now.Year(), now.Month(), now.Day(), 0, 0, 0, 0, now.Location())
}

func hashVid(vid string) string {
	sum := sha256.Sum256([]byte(strings.TrimSpace(strings.ToLower(vid))))
	return hex.EncodeToString(sum[:])
}

// ValidVisitorID 校验浏览器访客 ID（UUID）
func ValidVisitorID(vid string) bool {
	return vidUUIDRe.MatchString(strings.TrimSpace(vid))
}

// RecordPageView 记录一次页面浏览：PV 必增；合法 vid 首次出现当日才 UV+1
func (s *TelemetryService) RecordPageView(vid string, loggedIn bool) error {
	day := todayDate()

	err := s.db.Transaction(func(tx *gorm.DB) error {
		var st model.SiteDailyStats
		err := tx.Clauses(clause.Locking{Strength: "UPDATE"}).
			Where("date = ?", day).First(&st).Error
		if errors.Is(err, gorm.ErrRecordNotFound) {
			st = model.SiteDailyStats{Date: day}
			if err := tx.Create(&st).Error; err != nil {
				return err
			}
			// 重新锁住新建行
			if err := tx.Clauses(clause.Locking{Strength: "UPDATE"}).
				Where("date = ?", day).First(&st).Error; err != nil {
				return err
			}
		} else if err != nil {
			return err
		}

		updates := map[string]interface{}{
			"pv":         st.PV + 1,
			"updated_at": time.Now(),
		}
		if loggedIn {
			updates["logged_in_pv"] = st.LoggedInPV + 1
		}

		if ValidVisitorID(vid) {
			vis := model.SiteDailyVisitor{Date: day, VidHash: hashVid(vid)}
			res := tx.Clauses(clause.OnConflict{DoNothing: true}).Create(&vis)
			if res.Error != nil {
				return res.Error
			}
			if res.RowsAffected > 0 {
				updates["uv"] = st.UV + 1
			}
		}

		return tx.Model(&model.SiteDailyStats{}).Where("date = ?", day).Updates(updates).Error
	})
	return err
}