Docs site cleanup (#948)

* add language selector

* docs site cleanup

* review feedback

* code review comments

1 files changed, 55 insertions, 0 deletions

diff --git a/docs/src/components/RightSidebar/TableOfContents.tsx b/docs/src/components/RightSidebar/TableOfContents.tsx
new file mode 100644
index 000000000..803b05568
--- /dev/null
+++ b/docs/src/components/RightSidebar/TableOfContents.tsx
@@ -0,0 +1,55 @@
+import type { FunctionalComponent } from 'preact';
+import { h, Fragment } from 'preact';
+import { useState, useEffect, useRef } from 'preact/hooks';
+
+const TableOfContents: FunctionalComponent<{ headers: any[] }> = ({
+  headers = [],
+}) => {
+  const itemOffsets = useRef([]);
+  const [activeId, setActiveId] = useState<string>(undefined);
+
+  useEffect(() => {
+    const getItemOffsets = () => {
+      const titles = document.querySelectorAll('article :is(h1, h2, h3, h4)');
+      itemOffsets.current = Array.from(titles).map((title) => ({
+        id: title.id,
+        topOffset: title.getBoundingClientRect().top + window.scrollY,
+      }));
+    };
+
+    getItemOffsets();
+    window.addEventListener('resize', getItemOffsets);
+
+    return () => {
+      window.removeEventListener('resize', getItemOffsets);
+    };
+  }, []);
+
+  return (
+    <>
+      <h2 class="heading">On this page</h2>
+      <ul>
+        <li
+          class={`header-link depth-2 ${
+            activeId === 'overview' ? 'active' : ''
+          }`.trim()}
+        >
+          <a href="#overview">Overview</a>
+        </li>
+        {headers
+          .filter(({ depth }) => depth > 1 && depth < 4)
+          .map((header) => (
+            <li
+              class={`header-link depth-${header.depth} ${
+                activeId === header.slug ? 'active' : ''
+              }`.trim()}
+            >
+              <a href={`#${header.slug}`}>{header.text}</a>
+            </li>
+          ))}
+      </ul>
+    </>
+  );
+};
+
+export default TableOfContents;