package service

import (
	"errors"
	"log"
	"strconv"
	"time"

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

// DailyCheckinPoints 每日签到默认基础分（可被设置 points_checkin_base 覆盖）
const DailyCheckinPoints = 5

// maxStreakScan 连续天数最多向前回溯的天数
const maxStreakScan = 400

// ErrAlreadyCheckedIn 今日已签到
var ErrAlreadyCheckedIn = errors.New("今日已签到")

// CheckinStatus 签到状态（首页右栏与签到接口共用）
type CheckinStatus struct {
	CheckedToday bool `json:"checked_today"`
	Streak       int  `json:"streak"`       // 连续签到天数
	TotalPoints  int  `json:"total_points"` // 累计积分（可用余额）
	TodayPoints  int  `json:"today_points"` // 今日签到可得基础积分（连续加成另行入账，流水可见）
}

// CheckinService 每日签到
type CheckinService struct {
	db      *gorm.DB
	setting *SettingService
}

func NewCheckinService(db *gorm.DB) *CheckinService {
	return &CheckinService{db: db}
}

// WithSetting 注入站点设置（积分增长规则；未注入时用默认值）
func (s *CheckinService) WithSetting(setting *SettingService) *CheckinService {
	s.setting = setting
	return s
}

// rules 读取积分规则；未注入或读取失败回落默认值（签到可用性优先于规则精度）
func (s *CheckinService) rules() PointsRules {
	if s.setting == nil {
		return PointsRules{CheckinBase: DefaultPointsCheckinBase, StreakEveryDays: DefaultPointsStreakEveryDays}
	}
	rules, err := s.setting.PointsRules()
	if err != nil {
		log.Printf("[checkin] 读取积分规则失败，使用默认值: %v", err)
		return PointsRules{CheckinBase: DefaultPointsCheckinBase, StreakEveryDays: DefaultPointsStreakEveryDays}
	}
	return rules
}

// localDay 取本地时区零点日期
func localDay(t time.Time) time.Time {
	y, m, d := t.Date()
	return time.Date(y, m, d, 0, 0, 0, 0, t.Location())
}

// streakFrom 从 anchor（含）起按日倒推连续签到天数
func streakFrom(dates map[string]bool, anchor time.Time) int {
	streak := 0
	for i := 0; i < maxStreakScan; i++ {
		day := anchor.AddDate(0, 0, -i)
		if !dates[day.Format("2006-01-02")] {
			break
		}
		streak++
	}
	return streak
}

// streakDatesInTx 从事务连接查询 anchor 起回溯窗口内的签到日期集合
func streakDatesInTx(tx *gorm.DB, userID uint, anchor time.Time) (map[string]bool, error) {
	var dates []time.Time
	if err := tx.Model(&model.Checkin{}).
		Where("user_id = ? AND checkin_date >= ?", userID, anchor.AddDate(0, 0, -maxStreakScan)).
		Pluck("checkin_date", &dates).Error; err != nil {
		return nil, err
	}
	dateSet := make(map[string]bool, len(dates))
	for _, d := range dates {
		dateSet[localDay(d).Format("2006-01-02")] = true
	}
	return dateSet, nil
}

// Status 查询用户签到状态
func (s *CheckinService) Status(userID uint) (*CheckinStatus, error) {
	today := localDay(time.Now())
	base := s.rules().CheckinBase

	var todayRow model.Checkin
	err := s.db.Where("user_id = ? AND checkin_date::date = ?::date", userID, today).
		First(&todayRow).Error
	checkedToday := true
	if err != nil {
		if !errors.Is(err, gorm.ErrRecordNotFound) {
			return nil, err
		}
		checkedToday = false
	}

	// 连续天数：今日已签从今天起算，未签从昨天起算（今日尚未签不打断连续）
	anchor := today
	if !checkedToday {
		anchor = today.AddDate(0, 0, -1)
	}
	dateSet, err := streakDatesInTx(s.db, userID, anchor)
	if err != nil {
		return nil, err
	}

	var total int64
	if err := s.db.Model(&model.User{}).
		Where("id = ?", userID).
		Select("points").Scan(&total).Error; err != nil {
		return nil, err
	}

	return &CheckinStatus{
		CheckedToday: checkedToday,
		Streak:       streakFrom(dateSet, anchor),
		TotalPoints:  int(total),
		TodayPoints:  base,
	}, nil
}

// CheckIn 执行今日签到（每日一条，唯一索引兜底并发）。
// 基础分与连续签到里程碑加成在同一事务内入账（加成规则可配置：每满 N 天额外 +X）。
func (s *CheckinService) CheckIn(userID uint) (*CheckinStatus, error) {
	today := localDay(time.Now())
	rules := s.rules()

	var status *CheckinStatus
	err := s.db.Transaction(func(tx *gorm.DB) error {
		var count int64
		if err := tx.Model(&model.Checkin{}).
			Where("user_id = ? AND checkin_date::date = ?::date", userID, today).
			Count(&count).Error; err != nil {
			return err
		}
		if count > 0 {
			return ErrAlreadyCheckedIn
		}
		row := model.Checkin{
			UserID:      userID,
			CheckinDate: today,
			Points:      rules.CheckinBase,
		}
		if err := tx.Create(&row).Error; err != nil {
			return err
		}
		// 同步入账到用户积分余额
		if _, err := CreditTx(tx, userID, rules.CheckinBase, model.PointReasonCheckin, "checkin", row.ID, "每日签到"); err != nil {
			return err
		}
		// 连续签到里程碑加成（每满 N 天额外 +X；N=0 或加成=0 时关闭）
		if rules.StreakEveryDays > 0 && rules.StreakBonus > 0 {
			dateSet, err := streakDatesInTx(tx, userID, today)
			if err != nil {
				return err
			}
			if streak := streakFrom(dateSet, today); streak > 0 && streak%rules.StreakEveryDays == 0 {
				if _, err := CreditTx(tx, userID, rules.StreakBonus, model.PointReasonStreakBonus, "checkin", row.ID,
					"连续签到 "+strconv.Itoa(streak)+" 天奖励"); err != nil {
					return err
				}
			}
		}
		return nil
	})
	if err != nil {
		return nil, err
	}

	status, err = s.Status(userID)
	if err != nil {
		return nil, err
	}
	return status, nil
}