import { GraphNode } from "../graph";
import { NodeLength } from "../layout";
/**
 * A separation function that indicates how far apart nodes should be the layering / height assignment.
 *
 *
 * @remarks upper and lower are historic, since arbitrary graphs are handled,
 * there is no longer a notion of upper or lower and separation should return
 * the correct separation independent of nodes relations in the graph.
 */
export interface Separation<in NodeDatum = never, in LinkDatum = never> {
    /**
     * compute the necessary separation between two nodes
     *
     * `first` and `second` are `undefined` to indicate the separation from the
     * extents of the layout (0, or height). Both will never be `undefined`.
     *
     * @param first - one node to find the separation between
     * @param second - the other node to find the separation between
     * @returns sep - the minimum separation between the two nodes, regardless of which
     *   one is on top
     */
    (first: GraphNode<NodeDatum, LinkDatum> | undefined, second: GraphNode<NodeDatum, LinkDatum> | undefined): number;
}
/**
 * A separation derived from a length and a gap
 *
 * This is the separation function if each node has size `len` and between two
 * nodes there's an extra `gap`.
 */
export declare function sizedSeparation<NodeDatum, LinkDatum>(len: NodeLength<NodeDatum, LinkDatum>, gap: number): Separation<NodeDatum, LinkDatum>;
/** compute the number of crossings in a layered sugi node */
export declare function crossings(layers: readonly (readonly GraphNode[])[]): number;