From cab015431dff1d8b483fc0101eef7e8a63df47f1 Mon Sep 17 00:00:00 2001
From: Ben <3447705+bcabanes@users.noreply.github.com>
Date: Mon, 27 Mar 2023 16:17:49 -0400
Subject: [PATCH] feat(nx-dev): add table of content for documents

---
 .../feature-doc-viewer/src/lib/doc-viewer.tsx | 33 +++++--
 .../src/lib/table-of-contents.tsx             | 90 +++++++++++++++++++
 .../src/lib/use-headings-observer.ts          | 44 +++++++++
 nx-dev/ui-markdoc/src/index.ts                | 20 +++--
 4 files changed, 174 insertions(+), 13 deletions(-)
 create mode 100644 nx-dev/feature-doc-viewer/src/lib/table-of-contents.tsx
 create mode 100644 nx-dev/feature-doc-viewer/src/lib/use-headings-observer.ts

diff --git a/nx-dev/feature-doc-viewer/src/lib/doc-viewer.tsx b/nx-dev/feature-doc-viewer/src/lib/doc-viewer.tsx
index 06a2da8407e49c..dee9013980d424 100644
--- a/nx-dev/feature-doc-viewer/src/lib/doc-viewer.tsx
+++ b/nx-dev/feature-doc-viewer/src/lib/doc-viewer.tsx
@@ -8,6 +8,8 @@ import { Breadcrumbs, Footer } from '@nrwl/nx-dev/ui-common';
 import { renderMarkdown } from '@nrwl/nx-dev/ui-markdoc';
 import { NextSeo } from 'next-seo';
 import { useRouter } from 'next/router';
+import { useRef } from 'react';
+import { collectHeadings, TableOfContents } from './table-of-contents';
 
 export function DocViewer({
   document,
@@ -17,10 +19,14 @@ export function DocViewer({
   relatedDocuments: RelatedDocument[];
 }): JSX.Element {
   const router = useRouter();
+  const ref = useRef<HTMLDivElement | null>(null);
 
-  const { metadata, node } = renderMarkdown(document.content.toString(), {
-    filePath: document.filePath,
-  });
+  const { metadata, node, treeNode } = renderMarkdown(
+    document.content.toString(),
+    {
+      filePath: document.filePath,
+    }
+  );
 
   const vm = {
     title: metadata['title'] ?? document.name,
@@ -34,6 +40,7 @@ export function DocViewer({
         filePath: '',
       }
     ).node,
+    tableOfContent: collectHeadings(treeNode),
   };
 
   return (
@@ -75,11 +82,21 @@ export function DocViewer({
           </div>
           <div className="min-w-0 flex-auto pb-24 lg:pb-16">
             {/*MAIN CONTENT*/}
-            <div
-              data-document="main"
-              className="prose prose-slate dark:prose-invert max-w-none"
-            >
-              {vm.content}
+            <div className="relative">
+              <div
+                ref={ref}
+                data-document="main"
+                className="prose prose-slate dark:prose-invert w-full max-w-none 2xl:max-w-4xl"
+              >
+                {vm.content}
+              </div>
+              <div className="fixed top-36 right-[max(4rem,calc(50%-55rem))] z-20 hidden w-60 overflow-y-auto bg-white py-10 text-sm 2xl:block">
+                <TableOfContents
+                  elementRef={ref}
+                  path={router.basePath}
+                  headings={vm.tableOfContent}
+                />
+              </div>
             </div>
             {/*RELATED CONTENT*/}
             <div
diff --git a/nx-dev/feature-doc-viewer/src/lib/table-of-contents.tsx b/nx-dev/feature-doc-viewer/src/lib/table-of-contents.tsx
new file mode 100644
index 00000000000000..52806a60b958eb
--- /dev/null
+++ b/nx-dev/feature-doc-viewer/src/lib/table-of-contents.tsx
@@ -0,0 +1,90 @@
+import Link from 'next/link';
+import { cx } from 'nx-dev/ui-primitives';
+import { useHeadingsObserver } from './use-headings-observer';
+
+interface Heading {
+  id: string;
+  level: number;
+  title: string;
+}
+
+export function collectHeadings(
+  node: any,
+  sections: Heading[] = []
+): Heading[] {
+  if (node) {
+    if (node.name && node.name === 'Heading') {
+      const title = node.children[0];
+
+      if (typeof title === 'string') {
+        sections.push({
+          id: node.attributes['id'],
+          level: node.attributes['level'],
+          title,
+        });
+      }
+    }
+
+    if (node.children) {
+      for (const child of node.children) {
+        collectHeadings(child, sections);
+      }
+    }
+  }
+
+  return sections;
+}
+
+export function TableOfContents({
+  elementRef,
+  headings,
+  path,
+}: {
+  elementRef: any;
+  headings: Heading[];
+  path: string;
+}): JSX.Element {
+  const headingLevelTargets: number[] = [1, 2, 3]; // matching to: H1, H2, H3...
+  const items = headings.filter(
+    (item) => item.id && headingLevelTargets.includes(item.level)
+  );
+
+  const activeId = useHeadingsObserver(
+    elementRef,
+    {
+      threshold: [0, 0.25, 0.5, 0.75, 1],
+      root: null,
+      rootMargin: '-10% 0% -45% 0%',
+    },
+    headings.find((i) => i.level === 1)?.title || null
+  );
+
+  return (
+    <nav className="toc">
+      <span className="pl-4 font-medium">Quick reference</span>
+      {!!items.length ? (
+        <ul className="mt-4 flex-col">
+          {items.map((item) => {
+            const href = `${path}#${item.id}`;
+            return (
+              <li key={item.title}>
+                <Link
+                  href={href}
+                  className={cx(
+                    'block w-full border-l-4 border-slate-50 py-1 pl-3 transition hover:border-slate-500 hover:underline',
+                    {
+                      'border-slate-500 bg-slate-50': activeId === item.id,
+                      'pl-6': item.level === 3,
+                    }
+                  )}
+                >
+                  {item.title}
+                </Link>
+              </li>
+            );
+          })}
+        </ul>
+      ) : null}
+    </nav>
+  );
+}
diff --git a/nx-dev/feature-doc-viewer/src/lib/use-headings-observer.ts b/nx-dev/feature-doc-viewer/src/lib/use-headings-observer.ts
new file mode 100644
index 00000000000000..ac69b8daa59cc3
--- /dev/null
+++ b/nx-dev/feature-doc-viewer/src/lib/use-headings-observer.ts
@@ -0,0 +1,44 @@
+import { RefObject, useEffect, useState } from 'react';
+
+export function useHeadingsObserver(
+  elementRef: RefObject<Element>,
+  { threshold = 0, root = null, rootMargin = '0%' }: IntersectionObserverInit,
+  cachekey: string | null = null
+): string {
+  const [activeId, setActiveId] = useState<string>('');
+
+  useEffect(() => {
+    const handleObserver = (entries: IntersectionObserverEntry[]): void => {
+      for (const entry of entries) {
+        if (entry?.isIntersecting) setActiveId(entry.target.id);
+      }
+    };
+
+    const node = elementRef?.current; // DOM Ref
+    const hasIOSupport = !!window.IntersectionObserver;
+
+    if (!hasIOSupport || !node) return;
+    const observer = new IntersectionObserver(handleObserver, {
+      threshold,
+      root,
+      rootMargin,
+    });
+
+    const elements: NodeListOf<Element> = node.querySelectorAll('h1, h2, h3');
+    elements.forEach((e: Element) => {
+      observer.observe(e);
+    });
+
+    return () => observer.disconnect();
+
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [
+    elementRef?.current,
+    JSON.stringify(threshold),
+    root,
+    rootMargin,
+    cachekey,
+  ]);
+
+  return activeId;
+}
diff --git a/nx-dev/ui-markdoc/src/index.ts b/nx-dev/ui-markdoc/src/index.ts
index 6a7c2b30c33c82..cbe0e851f60b34 100644
--- a/nx-dev/ui-markdoc/src/index.ts
+++ b/nx-dev/ui-markdoc/src/index.ts
@@ -1,4 +1,11 @@
-import { Node, parse, renderers, Tokenizer, transform } from '@markdoc/markdoc';
+import {
+  Node,
+  parse,
+  RenderableTreeNode,
+  renderers,
+  Tokenizer,
+  transform,
+} from '@markdoc/markdoc';
 import { load as yamlLoad } from 'js-yaml';
 import React, { ReactNode } from 'react';
 import { Fence } from './lib/nodes/fence.component';
@@ -92,12 +99,14 @@ export const parseMarkdown: (markdown: string) => Node = (markdown) => {
 export const renderMarkdown: (
   documentContent: string,
   options: { filePath: string }
-) => { metadata: Record<string, any>; node: ReactNode } = (
-  documentContent: string,
-  options: { filePath: string } = { filePath: '' }
-): { metadata: Record<string, any>; node: ReactNode } => {
+) => {
+  metadata: Record<string, any>;
+  node: ReactNode;
+  treeNode: RenderableTreeNode;
+} = (documentContent, options = { filePath: '' }) => {
   const ast = parseMarkdown(documentContent);
   const configuration = getMarkdocCustomConfig(options.filePath);
+  const treeNode = transform(ast, configuration.config);
 
   return {
     metadata: ast.attributes['frontmatter']
@@ -106,5 +115,6 @@ export const renderMarkdown: (
     node: renderers.react(transform(ast, configuration.config), React, {
       components: configuration.components,
     }),
+    treeNode,
   };
 };