feat: add comments

internal/repository/social_graph_repo.go

@@ -324,9 +324,12 @@ func (r *NotificationRepo) ListByUser(ctx context.Context, userID string, limit,
 	rows, err := r.pg.Pool.Query(ctx, `
 		SELECT n.id, n.user_id, n.actor_id, n.kind, n.post_id, n.actor_count,
 		       n.created_at, n.read_at,
-		       u.name, u.handle, u.avatar_url
+		       u.name, u.handle, u.avatar_url,
+		       pu.handle
 		FROM notifications n
 		LEFT JOIN users u ON u.id = n.actor_id
+		LEFT JOIN posts p ON p.id = n.post_id
+		LEFT JOIN users pu ON pu.id = p.user_id
 		WHERE n.user_id = $1
 		  AND NOT EXISTS (
 		      SELECT 1 FROM notification_prefs np
@@ -344,7 +347,8 @@ func (r *NotificationRepo) ListByUser(ctx context.Context, userID string, limit,
 		var n model.Notification
 		if err := rows.Scan(&n.ID, &n.UserID, &n.ActorID, &n.Kind, &n.PostID, &n.ActorCount,
 			&n.CreatedAt, &n.ReadAt,
-			&n.ActorName, &n.ActorHandle, &n.ActorAvatar); err != nil {
+			&n.ActorName, &n.ActorHandle, &n.ActorAvatar,
+			&n.PostAuthorHandle); err != nil {
 			return nil, fmt.Errorf("scan notification: %w", err)
 		}
 		out = append(out, n)
@@ -400,6 +404,36 @@ func (r *NotificationRepo) CreateMention(ctx context.Context, userID, actorID, p
 	return nil
 }
 
+// CreateComment persists a comment/reply notification linked to the post.
+// kind is 'post_comment' (to the post author) or 'comment_reply' (to the
+// replied-to comment's author). Like mentions, no aggregation.
+func (r *NotificationRepo) CreateComment(ctx context.Context, userID, actorID, postID, kind string) error {
+	if _, err := r.pg.Pool.Exec(ctx,
+		`INSERT INTO notifications (user_id, actor_id, kind, post_id)
+		 VALUES ($1, $2, $3, $4)`,
+		userID, actorID, kind, postID,
+	); err != nil {
+		return fmt.Errorf("create comment notification: %w", err)
+	}
+	return nil
+}
+
+// PostAuthorHandle returns the handle of the user who owns the post, for
+// building a deep-link. Empty string (no error) when the post is gone.
+func (r *NotificationRepo) PostAuthorHandle(ctx context.Context, postID string) (string, error) {
+	var h string
+	err := r.pg.Pool.QueryRow(ctx,
+		`SELECT u.handle FROM posts p JOIN users u ON u.id = p.user_id WHERE p.id = $1`,
+		postID).Scan(&h)
+	if errors.Is(err, pgx.ErrNoRows) {
+		return "", nil
+	}
+	if err != nil {
+		return "", fmt.Errorf("post author handle: %w", err)
+	}
+	return h, nil
+}
+
 // CountUnread returns how many of a recipient's notifications are unread,
 // excluding kinds the user has turned off for the in-app channel (matching
 // ListByUser, so the badge never counts rows the feed won't show).