export type ITreeNode<T = Record<string, unknown>> = {
    id: string;
    label: string;
    data?: T;
    children?: ITreeNode<T>[];
    isParent?: boolean;
};
export type IFlatTreeNode<T = Record<string, unknown>> = {
    node: ITreeNode<T>;
    depth: number;
    hasChildren: boolean;
    parentId: string | undefined;
};
export type ITreeNodeState = {
    isFocused: boolean;
    isExpanded: boolean;
    isSelected: boolean;
    isLoading: boolean;
    depth: number;
    hasChildren: boolean;
};
/**
 * Flattens a tree into a visible list based on expansion state.
 * Only expanded nodes' children are included.
 *
 * Analogy (Naruto): unrolling a scroll — collapsed sections stay sealed,
 * expanded sections reveal their contents.
 */
export declare function flattenTree<T>(nodes: ITreeNode<T>[], expandedIds: ReadonlySet<string>, depth?: number, parentId?: string | undefined): IFlatTreeNode<T>[];
export declare function findParentId<T>(flatNodes: IFlatTreeNode<T>[], nodeId: string): string | undefined;
export declare function findFirstChildId<T>(flatNodes: IFlatTreeNode<T>[], nodeId: string, expandedIds: ReadonlySet<string>): string | undefined;
export type IViewport = {
    fromIndex: number;
    toIndex: number;
};
export declare function computeViewport(totalCount: number, focusedIndex: number, visibleCount: number, current: IViewport): IViewport;
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