package repository

import (
	"context"
	"errors"
	"fmt"

	"github.com/topfans/backend/pkg/logger"
	"github.com/topfans/backend/services/notificationService/model"
	"go.uber.org/zap"
	"gorm.io/gorm"
)

// NotificationStatsRepository 通知未读计数仓储（操作 public.notification_stats 表）。
//
// 设计：所有写方法要求事务上下文（service 层在事务回调内同时写 notifications 与 stats）；
// Get 是单条读，使用仓储默认 db。
type NotificationStatsRepository struct {
	db *gorm.DB
}

// NewNotificationStatsRepository 创建未读计数仓储。
func NewNotificationStatsRepository(db *gorm.DB) *NotificationStatsRepository {
	return &NotificationStatsRepository{db: db}
}

// IncrementByType 在事务内对指定 type 未读数 +1（total +1）。
func (r *NotificationStatsRepository) IncrementByType(ctx context.Context, tx *gorm.DB, userID, starID int64, ntype string, now int64) error {
	if tx == nil {
		return errors.New("IncrementByType must be called within a transaction")
	}
	col, err := typeToColumn(ntype)
	if err != nil {
		return err
	}
	// 使用 ON CONFLICT 做 upsert：首次写入时插入 1，后续累加。
	// GORM Exec 支持 PostgreSQL 占位符 $1/$2/$3。
	query := fmt.Sprintf(`
		INSERT INTO public.notification_stats (user_id, star_id, %s, total_unread_count, updated_at)
		VALUES ($1, $2, 1, 1, $3)
		ON CONFLICT (user_id, star_id) DO UPDATE SET
			%[1]s = public.notification_stats.%[1]s + 1,
			total_unread_count = public.notification_stats.total_unread_count + 1,
			updated_at = $3
	`, col)
	if err := tx.WithContext(ctx).Exec(query, userID, starID, now).Error; err != nil {
		logger.Logger.Error("failed to increment notification stats",
			zap.Int64("user_id", userID),
			zap.Int64("star_id", starID),
			zap.String("type", ntype),
			zap.Error(err))
		return fmt.Errorf("increment stats: %w", err)
	}
	return nil
}

// DecrementByType 在事务内对指定 type 未读数 -N（total -N）。
//
// 使用 GREATEST(0, ...) 防止计数被减为负数。
func (r *NotificationStatsRepository) DecrementByType(ctx context.Context, tx *gorm.DB, userID, starID int64, ntype string, delta int, now int64) error {
	if delta <= 0 {
		return nil
	}
	if tx == nil {
		return errors.New("DecrementByType must be called within a transaction")
	}
	col, err := typeToColumn(ntype)
	if err != nil {
		return err
	}
	query := fmt.Sprintf(`
		UPDATE public.notification_stats
		SET %s = GREATEST(0, %[1]s - $3),
		    total_unread_count = GREATEST(0, total_unread_count - $3),
		    updated_at = $4
		WHERE user_id = $1 AND star_id = $2
	`, col)
	if err := tx.WithContext(ctx).Exec(query, userID, starID, delta, now).Error; err != nil {
		logger.Logger.Error("failed to decrement notification stats",
			zap.Int64("user_id", userID),
			zap.Int64("star_id", starID),
			zap.String("type", ntype),
			zap.Int("delta", delta),
			zap.Error(err))
		return fmt.Errorf("decrement stats: %w", err)
	}
	return nil
}

// ResetByType 把指定 type 未读数置 0（同时从 total 中减去）。
//
// ntype 为空字符串表示重置全部（所有 type + total）。
func (r *NotificationStatsRepository) ResetByType(ctx context.Context, tx *gorm.DB, userID, starID int64, ntype string, now int64) error {
	if tx == nil {
		return errors.New("ResetByType must be called within a transaction")
	}
	gdb := tx.WithContext(ctx)
	if ntype == "" {
		return gdb.Exec(`
			UPDATE public.notification_stats
			SET like_unread_count = 0, system_unread_count = 0,
			    activity_unread_count = 0, total_unread_count = 0,
			    updated_at = $3
			WHERE user_id = $1 AND star_id = $2
		`, userID, starID, now).Error
	}
	col, err := typeToColumn(ntype)
	if err != nil {
		return err
	}
	// 仅减去本类型的数值，避免误扣其它类型的累计。
	query := fmt.Sprintf(`
		UPDATE public.notification_stats
		SET %s = 0,
		    total_unread_count = GREATEST(0, total_unread_count - %[1]s),
		    updated_at = $3
		WHERE user_id = $1 AND star_id = $2
	`, col)
	if err := gdb.Exec(query, userID, starID, now).Error; err != nil {
		return fmt.Errorf("reset stats: %w", err)
	}
	return nil
}

// Get 拉取 user+star 的统计行；记录不存在时返回零值。
func (r *NotificationStatsRepository) Get(ctx context.Context, userID, starID int64) (*model.NotificationStats, error) {
	s := &model.NotificationStats{}
	err := r.db.WithContext(ctx).Raw(`
		SELECT user_id, star_id, like_unread_count, system_unread_count,
		       activity_unread_count, total_unread_count, updated_at
		FROM public.notification_stats
		WHERE user_id = $1 AND star_id = $2
	`, userID, starID).Row().Scan(
		&s.UserID, &s.StarID, &s.LikeUnreadCount, &s.SystemUnreadCount,
		&s.ActivityUnreadCount, &s.TotalUnreadCount, &s.UpdatedAt,
	)
	if err != nil {
		if errors.Is(err, gorm.ErrRecordNotFound) {
			return &model.NotificationStats{UserID: userID, StarID: starID}, nil
		}
		return nil, fmt.Errorf("get stats: %w", err)
	}
	return s, nil
}

// typeToColumn 将通知类型映射到 stats 表的列名。
func typeToColumn(ntype string) (string, error) {
	switch ntype {
	case "like":
		return "like_unread_count", nil
	case "system":
		return "system_unread_count", nil
	case "activity":
		return "activity_unread_count", nil
	default:
		return "", fmt.Errorf("invalid notification type: %s", ntype)
	}
}