diagrams-drawio/scripts/src/services/authoring-router/orthogonal-router.ts

import type { DiagramEdge, DiagramGeometry, DiagramNode, DiagramPage, DiagramPoint } from "../../model/diagram-ir.js";

interface Obstacle extends DiagramGeometry {
  id: string;
}

function center(geometry: DiagramGeometry): DiagramPoint {
  return { x: geometry.x + geometry.width / 2, y: geometry.y + geometry.height / 2 };
}

function endpointPair(source: DiagramGeometry, target: DiagramGeometry): { source: DiagramPoint; target: DiagramPoint } {
  const a = center(source);
  const b = center(target);
  const dx = b.x - a.x;
  const dy = b.y - a.y;
  if (Math.abs(dx) >= Math.abs(dy)) {
    return dx >= 0
      ? { source: { x: source.x + source.width, y: a.y }, target: { x: target.x, y: b.y } }
      : { source: { x: source.x, y: a.y }, target: { x: target.x + target.width, y: b.y } };
  }
  return dy >= 0
    ? { source: { x: a.x, y: source.y + source.height }, target: { x: b.x, y: target.y } }
    : { source: { x: a.x, y: source.y }, target: { x: b.x, y: target.y + target.height } };
}

function outwardStub(point: DiagramPoint, geometry: DiagramGeometry, distance: number): DiagramPoint {
  const middle = center(geometry);
  return {
    x: point.x + Math.sign(point.x - middle.x) * distance,
    y: point.y + Math.sign(point.y - middle.y) * distance,
  };
}

function compactPath(path: DiagramPoint[]): DiagramPoint[] {
  const deduped = path.filter((point, index) => index === 0 || point.x !== path[index - 1].x || point.y !== path[index - 1].y);
  return deduped.filter((point, index) => {
    if (index === 0 || index === deduped.length - 1) return true;
    const previous = deduped[index - 1];
    const next = deduped[index + 1];
    return !((previous.x === point.x && point.x === next.x) || (previous.y === point.y && point.y === next.y));
  });
}

function segmentIntersectsRect(a: DiagramPoint, b: DiagramPoint, rect: Obstacle, padding: number): boolean {
  const left = rect.x - padding;
  const right = rect.x + rect.width + padding;
  const top = rect.y - padding;
  const bottom = rect.y + rect.height + padding;
  if (a.y === b.y) {
    return a.y > top && a.y < bottom && Math.max(Math.min(a.x, b.x), left) < Math.min(Math.max(a.x, b.x), right);
  }
  if (a.x === b.x) {
    return a.x > left && a.x < right && Math.max(Math.min(a.y, b.y), top) < Math.min(Math.max(a.y, b.y), bottom);
  }
  return true;
}

function pathClear(path: DiagramPoint[], obstacles: Obstacle[], padding: number): boolean {
  for (let index = 0; index < path.length - 1; index += 1) {
    for (const obstacle of obstacles) {
      if (segmentIntersectsRect(path[index], path[index + 1], obstacle, padding)) return false;
    }
  }
  return true;
}

function pathLength(path: DiagramPoint[]): number {
  let total = 0;
  for (let index = 0; index < path.length - 1; index += 1) {
    total += Math.abs(path[index + 1].x - path[index].x) + Math.abs(path[index + 1].y - path[index].y);
  }
  return total;
}

function routedStyle(style?: string): string {
  const base = style ?? "rounded=0;orthogonalLoop=1;html=1;";
  if (/edgeStyle=[^;]*;?/.test(base)) return base.replace(/edgeStyle=[^;]*;?/, "edgeStyle=none;");
  return `edgeStyle=none;${base}`;
}

function absoluteGeometryById(page: DiagramPage): Map<string, DiagramGeometry> {
  const nodes = new Map(page.nodes.map((node) => [node.id, node]));
  const result = new Map<string, DiagramGeometry>();
  const resolving = new Set<string>();
  const resolve = (id: string): DiagramGeometry | undefined => {
    const cached = result.get(id);
    if (cached) return cached;
    const node = nodes.get(id);
    if (!node?.geometry || resolving.has(id)) return undefined;
    resolving.add(id);
    const parent = node.parentId ? resolve(node.parentId) : undefined;
    resolving.delete(id);
    const absolute = {
      ...node.geometry,
      x: node.geometry.x + (parent?.x ?? 0),
      y: node.geometry.y + (parent?.y ?? 0),
    };
    result.set(id, absolute);
    return absolute;
  };
  for (const id of nodes.keys()) resolve(id);
  return result;
}

// Height of a container's label band. Mirrors ir-to-drawio's default container style (swimlane with
// startSize=30) and draw.io's own swimlane default (40) when a custom style omits startSize.
function headerHeight(node: DiagramNode): number {
  if (node.style === undefined) return node.kind === "container" ? 30 : 0;
  const explicit = /(?:^|;)startSize=(\d+(?:\.\d+)?)/.exec(node.style);
  if (explicit) return Number(explicit[1]);
  return /(?:^|;)swimlane(?:;|$)/.test(node.style) ? 40 : 0;
}

function ancestorIds(page: DiagramPage, id: string): Set<string> {
  const nodes = new Map(page.nodes.map((node) => [node.id, node]));
  const ancestors = new Set<string>();
  let parentId = nodes.get(id)?.parentId;
  while (parentId && !ancestors.has(parentId)) {
    ancestors.add(parentId);
    parentId = nodes.get(parentId)?.parentId;
  }
  return ancestors;
}

function routeEdge(edge: DiagramEdge, page: DiagramPage, geometries: Map<string, DiagramGeometry>, padding: number, grid: number): DiagramEdge {
  if (edge.waypoints?.length) return { ...edge, waypoints: edge.waypoints.map((point) => ({ ...point })) };
  const source = geometries.get(edge.source);
  const target = geometries.get(edge.target);
  if (!source || !target) return { ...edge };
  const snap = (value: number) => Math.round(value / grid) * grid;
  if (edge.source === edge.target) {
    const right = snap(source.x + source.width + padding * 2);
    const top = snap(source.y - padding * 2);
    return {
      ...edge,
      style: routedStyle(edge.style),
      waypoints: [
        { x: right, y: snap(source.y + source.height / 2) },
        { x: right, y: top },
        { x: snap(source.x + source.width / 2), y: top },
      ],
    };
  }
  const endpoints = endpointPair(source, target);
  const endpointAncestors = new Set([...ancestorIds(page, edge.source), ...ancestorIds(page, edge.target)]);
  // Containers enclosing an endpoint may be crossed, except for their header band: a route through the
  // label bar (or along its bottom line) merges visually with the container border.
  const obstacles: Obstacle[] = page.nodes
    .filter((node) => node.id !== edge.source && node.id !== edge.target && geometries.has(node.id))
    .flatMap((node) => {
      const geometry = geometries.get(node.id)!;
      if (!endpointAncestors.has(node.id)) return [{ id: node.id, ...geometry }];
      const header = headerHeight(node);
      return header > 0 ? [{ id: node.id, ...geometry, height: header }] : [];
    });
  const sourceStub = outwardStub(endpoints.source, source, padding);
  const targetStub = outwardStub(endpoints.target, target, padding);
  const middleX = snap((sourceStub.x + targetStub.x) / 2);
  const middleY = snap((sourceStub.y + targetStub.y) / 2);

  const directCandidates: DiagramPoint[][] = endpoints.source.x === endpoints.target.x || endpoints.source.y === endpoints.target.y
    ? [[endpoints.source, endpoints.target]]
    : [
      [endpoints.source, sourceStub, { x: middleX, y: sourceStub.y }, { x: middleX, y: targetStub.y }, targetStub, endpoints.target],
      [endpoints.source, sourceStub, { x: sourceStub.x, y: middleY }, { x: targetStub.x, y: middleY }, targetStub, endpoints.target],
    ];
  const minY = Math.min(source.y, target.y, ...obstacles.map((item) => item.y));
  const maxY = Math.max(source.y + source.height, target.y + target.height, ...obstacles.map((item) => item.y + item.height));
  const minX = Math.min(source.x, target.x, ...obstacles.map((item) => item.x));
  const maxX = Math.max(source.x + source.width, target.x + target.width, ...obstacles.map((item) => item.x + item.width));
  const corridorCandidates: DiagramPoint[][] = [
    [endpoints.source, sourceStub, { x: sourceStub.x, y: snap(minY - padding * 2) }, { x: targetStub.x, y: snap(minY - padding * 2) }, targetStub, endpoints.target],
    [endpoints.source, sourceStub, { x: sourceStub.x, y: snap(maxY + padding * 2) }, { x: targetStub.x, y: snap(maxY + padding * 2) }, targetStub, endpoints.target],
    [endpoints.source, sourceStub, { x: snap(minX - padding * 2), y: sourceStub.y }, { x: snap(minX - padding * 2), y: targetStub.y }, targetStub, endpoints.target],
    [endpoints.source, sourceStub, { x: snap(maxX + padding * 2), y: sourceStub.y }, { x: snap(maxX + padding * 2), y: targetStub.y }, targetStub, endpoints.target],
  ];

  const candidates = [...directCandidates, ...corridorCandidates]
    .map(compactPath)
    .filter((path) => pathClear(path, obstacles, padding))
    .sort((a, b) => pathLength(a) - pathLength(b) || JSON.stringify(a).localeCompare(JSON.stringify(b)));
  const selected = candidates[0];
  if (!selected) return { ...edge };
  return { ...edge, style: routedStyle(edge.style), waypoints: selected.slice(1, -1) };
}

export function routePageEdges(page: DiagramPage, padding = 10): DiagramPage {
  const grid = page.layout?.gridSize ?? 10;
  const geometries = absoluteGeometryById(page);
  return {
    ...page,
    nodes: page.nodes.map((node) => ({ ...node, geometry: node.geometry ? { ...node.geometry } : undefined })),
    edges: page.edges.map((edge) => routeEdge(edge, page, geometries, padding, grid)),
  };
}