doc.silverstripe.org/src/utils/nodes.ts

import { useStaticQuery } from 'gatsby';
import { graphql } from 'gatsby';
import { HierarchyQuery, SilverstripeDocument } from '../types';
import sortFiles from './sortFiles';

let __nodes: SilverstripeDocument[] | undefined;
let __path: string | null = null;
let __currentNode: SilverstripeDocument | null = null;
let __home: SilverstripeDocument | null = null;

const childrenMap = new Map();
const navChildrenMap = new Map();
const siblingMap = new Map();
const parentMap = new Map();

const getNodes = (): SilverstripeDocument[] => {
  if (__nodes) {
    return __nodes;
  }
  const result:HierarchyQuery = useStaticQuery(graphql`
    {
      allSilverstripeDocument {
        nodes {
            title
            summary
            isIndex
            introduction
            icon
            hideChildren
            slug
            parentSlug
            fileTitle
            fileAbsolutePath
        }
      }
    }
  `
  );
  __nodes = result.allSilverstripeDocument.nodes.map(node => ({
    ...node,
  }));

  return __nodes;
};

const getChildren = (
  node: SilverstripeDocument,
  includeFolders: boolean = true
): SilverstripeDocument[] => {
  const sku = `${node.slug}${includeFolders ? '1' : '0'}`;
  if (childrenMap.has(sku)) {
    return childrenMap.get(sku);
  }
  const nodes = getNodes();
  let children: SilverstripeDocument[] = [];
  if (node.isIndex) {
    children = nodes.filter(n => {
      return n.parentSlug === node.slug && (includeFolders || !n.isIndex);
    }).sort(sortFiles);
  }
  childrenMap.set(sku, children);

  return childrenMap.get(sku);
}

const getNavChildren = (node: SilverstripeDocument): SilverstripeDocument[] => {
  if (navChildrenMap.has(node.slug)) {
    return navChildrenMap.get(node.slug);
  }
  let children: SilverstripeDocument[] = [];
  if (!node.hideChildren) {
    children = getChildren(node, true).filter(n => !n.hideSelf);
  }

  navChildrenMap.set(node.slug, children);

  return navChildrenMap.get(node.slug);
};

const getSiblings = (node: SilverstripeDocument): SilverstripeDocument[] => {  
  if (siblingMap.has(node.slug)) {
    return siblingMap.get(node.slug);
  }
  const nodes = getNodes();
  const siblings = nodes.filter(n => n.parentSlug === node.parentSlug);

  siblingMap.set(node.slug, siblings);

  return siblingMap.get(node.slug);
};

const getParent = (node: SilverstripeDocument): SilverstripeDocument | null => {
  if (parentMap.has(node.slug)) {
    return parentMap.get(node.slug);
  }

  const nodes = getNodes();
  const parent = nodes.find(n => n.slug === node.parentSlug) || null;

  parentMap.set(node.slug, parent);

  return parentMap.get(node.slug);
};

const getCurrentNode = (): SilverstripeDocument | null => {
    const browserPath = typeof window !== 'undefined' ? window.location.pathname : '/';
    if (!__path || __path !== browserPath) {
        __path = browserPath;
        const nodes = getNodes();
        __currentNode = nodes.find(n => n.slug === __path) || null;
    }
    return __currentNode || null;
};

const getHomePage = (): SilverstripeDocument | null => {
  if (__home) {
    return __home;
  }
  const nodes = getNodes();
  const homePage = nodes.find(n => n.slug === '/en/4/') || null;

  __home = homePage;

  return __home;
};

export {
  getNodes,
  getChildren,
  getSiblings,
  getParent,
  getCurrentNode,
  getHomePage,
  getNavChildren,
};