package gameking

import (
	"context"
	"net/http"
	"time"

	"chatapp3-golang/internal/model"

	"gorm.io/gorm"
	"gorm.io/gorm/clause"
)

// loadOrCreateBackfillState 先建立活动级水位行，后续并发补数才能通过行锁检测游标竞争，
// 避免较慢请求把较快请求已经推进的复合游标覆盖回旧位置。
func (s *Service) loadOrCreateBackfillState(ctx context.Context, activity model.YumiGameKingActivity) (model.YumiGameKingBackfillState, error) {
	now := time.Now()
	start := activity.StartTime
	initial := model.YumiGameKingBackfillState{
		ActivityID: activity.ID, LastOccurredAt: &start, CreateTime: now, UpdateTime: now,
	}
	if err := s.db.WithContext(ctx).Clauses(clause.OnConflict{DoNothing: true}).Create(&initial).Error; err != nil {
		return initial, err
	}
	var row model.YumiGameKingBackfillState
	if err := s.db.WithContext(ctx).Where("activity_id = ?", activity.ID).First(&row).Error; err != nil {
		return row, err
	}
	return row, nil
}

// adoptBackfillCursor 只兼容 migration 060 上线前调用方已经保存的合法 lastId；水位一旦
// 非零，调用方就不能跳转或回退游标。
func (s *Service) adoptBackfillCursor(ctx context.Context, activityID int64, cursor model.TaskCenterEventArchiveOutbox) (model.YumiGameKingBackfillState, error) {
	var state model.YumiGameKingBackfillState
	err := s.db.WithContext(ctx).Transaction(func(tx *gorm.DB) error {
		if err := tx.Clauses(clause.Locking{Strength: "UPDATE"}).Where("activity_id = ?", activityID).First(&state).Error; err != nil {
			return err
		}
		if state.LastOutboxID != 0 {
			return NewAppError(http.StatusConflict, "backfill_cursor_conflict", "persisted backfill cursor changed; reload and retry")
		}
		now := time.Now()
		if err := tx.Model(&model.YumiGameKingBackfillState{}).Where("activity_id = ?", activityID).Updates(map[string]any{
			"last_outbox_id": cursor.ID, "last_occurred_at": cursor.OccurredAt,
			"completed": false, "update_time": now,
		}).Error; err != nil {
			return err
		}
		state.LastOutboxID = cursor.ID
		state.LastOccurredAt = &cursor.OccurredAt
		state.UpdateTime = now
		return nil
	})
	return state, err
}

func (s *Service) persistBackfillState(
	ctx context.Context,
	activityID, expectedLastID int64,
	nextLastID int64,
	nextOccurredAt time.Time,
	scanned, accepted int,
	completed bool,
) error {
	return s.db.WithContext(ctx).Transaction(func(tx *gorm.DB) error {
		var locked model.YumiGameKingBackfillState
		if err := tx.Clauses(clause.Locking{Strength: "UPDATE"}).Where("activity_id = ?", activityID).First(&locked).Error; err != nil {
			return err
		}
		if locked.LastOutboxID != expectedLastID {
			// 本页可能已经通过幂等 ledger 入账；不覆盖赢家水位，调用方重读后重放即可安全收敛。
			return NewAppError(http.StatusConflict, "backfill_cursor_conflict", "another backfill request advanced the persisted cursor; reload and retry")
		}
		return tx.Model(&model.YumiGameKingBackfillState{}).Where("activity_id = ?", activityID).Updates(map[string]any{
			"last_outbox_id": nextLastID, "last_occurred_at": nextOccurredAt,
			"scanned_rows":  gorm.Expr("scanned_rows + ?", scanned),
			"accepted_rows": gorm.Expr("accepted_rows + ?", accepted),
			"completed":     completed, "update_time": time.Now(),
		}).Error
	})
}