import { CollectionViewGroup } from './CollectionViewGroup';
export interface GroupDisplayRow<T> {
    kind: 'group';
    group: CollectionViewGroup<T>;
    level: number;
    /** Stable identity across rebuilds, used to remember collapse state. */
    pathKey: string;
    collapsed: boolean;
}
export interface DataDisplayRow {
    kind: 'data';
    /** Index into the collection view's leaf array. */
    viewIndex: number;
}
export type DisplayRow<T> = GroupDisplayRow<T> | DataDisplayRow;
/**
 * Flattens a collection view's group tree into the linear list of rows the grid
 * actually renders: a header row per group followed by its data rows, with the
 * subtree omitted when a group is collapsed. Collapse state is keyed by group
 * path so it survives rebuilds (re-sort, filter, regroup).
 */
export declare class GroupRowModel<T = Record<string, unknown>> {
    private rows;
    private collapsed;
    private allKeys;
    get length(): number;
    get active(): boolean;
    rebuild(groups: CollectionViewGroup<T>[]): void;
    rowAt(index: number): DisplayRow<T> | undefined;
    isCollapsed(pathKey: string): boolean;
    toggle(pathKey: string): void;
    collapseAll(): void;
    expandAll(): void;
    /** The path keys of every collapsed group, for saving state. */
    collapsedKeys(): string[];
    /** Replace the collapsed set (used when restoring saved state). */
    setCollapsed(keys: string[]): void;
}