1 files changed, 37 insertions, 0 deletions
diff --git a/src/utils/generateToc.ts b/src/utils/generateToc.ts
new file mode 100644
index 0000000..f63f0bf
--- /dev/null
+++ b/src/utils/generateToc.ts
@@ -0,0 +1,37 @@
+// Heavy inspiration from starlight: https://github.com/withastro/starlight/blob/main/packages/starlight/utils/generateToC.ts
+import type { MarkdownHeading } from "astro";
+
+export interface TocItem extends MarkdownHeading {
+	children: TocItem[];
+}
+
+interface TocOpts {
+	maxHeadingLevel?: number | undefined;
+	minHeadingLevel?: number | undefined;
+}
+
+/** Inject a ToC entry as deep in the tree as its `depth` property requires. */
+function injectChild(items: TocItem[], item: TocItem): void {
+	const lastItem = items.at(-1);
+	if (!lastItem || lastItem.depth >= item.depth) {
+		items.push(item);
+	} else {
+		injectChild(lastItem.children, item);
+		return;
+	}
+}
+
+export function generateToc(
+	headings: ReadonlyArray<MarkdownHeading>,
+	{ maxHeadingLevel = 4, minHeadingLevel = 2 }: TocOpts = {},
+) {
+	// by default this ignores/filters out h1 and h5 heading(s)
+	const bodyHeadings = headings.filter(
+		({ depth }) => depth >= minHeadingLevel && depth <= maxHeadingLevel,
+	);
+	const toc: Array<TocItem> = [];
+
+	for (const heading of bodyHeadings) injectChild(toc, { ...heading, children: [] });
+
+	return toc;
+}