bpmn-optimizer/src/optimizer/steps/EdgeRoutingStep.ts

import AlgorithmStep from "../AlgorithmStep.js";
import {EdgeSubdivisions, SiguiyamaContext} from "../siguiyama/SiguiyamaContext.js";
import EdgeRoutingStepError from "../../errors/optimizer/EdgeRoutingStepError.js";
import Node from "../../graph/node/Node.js";
import Edge from "../../graph/edge/Edge.js";
import DummyNode from "../../graph/node/DummyNode.js";
import DummyEdge from "../../graph/edge/DummyEdge.js";
import Graph from "../../graph/Graph.js";
import Layering from "../../graph/layering/Layering.js";

export default class EdgeRoutingStep extends AlgorithmStep<SiguiyamaContext> {
	public constructor() {
		super(EdgeRoutingStep.name);
	}

	public run(context: SiguiyamaContext) : void {
		const { layering, graph, edgeSubdivisions } = context;

		if(!layering)
			throw new EdgeRoutingStepError("Layering is null or undefined");
		if(!graph)
			throw new EdgeRoutingStepError("Graph is null or undefined");
		if(!edgeSubdivisions)
			throw new EdgeRoutingStepError("Edge Subdivisions are null or undefined");

		this.routeEdges(graph, layering, edgeSubdivisions);
	}

	private routeEdges(graph: Graph<Node, Edge<Node>>, layering: Layering<Node, Edge<Node>>, edgeSubdivisions: EdgeSubdivisions<Node, Edge<Node>>): void {
		const edges = graph.getEdges();

		for(const edge of edges) {
			const from = edge.getFrom();
			const to = edge.getTo();
			const fromNodeIndex = this.getNodeIndex(layering, from);
			const toNodeIndex = this.getNodeIndex(layering, to);

			if(fromNodeIndex === -1 || toNodeIndex === -1 || fromNodeIndex === toNodeIndex)
				continue;

			const fromLayerIndex = layering.getNodeLayerIndex(from);
			if(fromLayerIndex === -1)
				continue;

			const targetRowIndex = fromNodeIndex > toNodeIndex ? fromNodeIndex - 1 : fromNodeIndex + 1;
			const neighborRowCenter = this.getRowCenter(layering, targetRowIndex);
			if(neighborRowCenter === null)
				continue;

			const fromCenterY = from.getY() + from.getHeight() / 2;
			const routedNode = new DummyNode(
				from.getX() + from.getWidth() / 2,
				(fromCenterY + neighborRowCenter) / 2
			);

			layering.addToLayer(fromLayerIndex, routedNode);
			graph.addNode(routedNode);

			const left = new DummyEdge(from, routedNode);
			const right = new DummyEdge(routedNode, to);

			graph.addEdge(left);
			graph.addEdge(right);
			graph.removeEdge(edge.getId());

			edgeSubdivisions.set(edge, { left, right });
		}
	}

	private getRowCenter(layering: Layering<Node, Edge<Node>>, rowIndex: number): number | null {
		if(rowIndex < 0)
			return null;

		for(const layer of layering.getLayers()) {
			const node = layer.getNodes().at(rowIndex);
			if(node)
				return node.getY() + node.getHeight() / 2;
		}

		return null;
	}

	private getNodeIndex(layering: Layering<Node, Edge<Node>>, node: Node) : number {
		const layerIndex = layering.getNodeLayerIndex(node);
		if(layerIndex === -1)
			return -1;

		return layering.getLayers()[layerIndex]!.getNodes().indexOf(node);
	}
}