@graphty/layout/src/algorithms/planarity/check.ts

graph layout algorithms based on networkx

/**
 * Main planarity checking function
 */

import { Graph, Node, Edge, Embedding } from '../../types';
import { isK5, isK33 } from './special-graphs';
import { lrPlanarityTest } from './lr-test';
import { createTriangulationEmbedding } from './embedding';

/**
 * Check if graph is planar using a simplified version of Boyer-Myrvold algorithm.
 * Returns planarity and embedding information.
 * 
 * @param G - Graph
 * @param nodes - List of nodes
 * @param edges - List of edges
 * @returns Object containing isPlanar flag and embedding
 */
export function checkPlanarity(
  G: Graph,
  nodes: Node[],
  edges: Edge[],
  seed: number | null = null
): { isPlanar: boolean; embedding: Embedding | null } {
  // For small graphs (n <= 4), all are planar
  if (nodes.length <= 4) {
    return { isPlanar: true, embedding: createTriangulationEmbedding(nodes, edges, seed) };
  }

  // For K5 (complete graph with 5 nodes) and K3,3 (complete bipartite with 3,3 nodes)
  // these are not planar by Kuratowski's theorem
  if (isK5(nodes, edges) || isK33(nodes, edges)) {
    return { isPlanar: false, embedding: null };
  }

  // For other graphs, use LR algorithm (Left-Right Planarity Test)
  const result = lrPlanarityTest(nodes, edges, seed);
  return result;
}