import { useCallback } from 'react'

import type { useRouter } from 'next/router'

type Router = ReturnType<typeof useRouter>

// Session-lived de-dupe set. Module scope (not a per-component useRef) so it

// survives the sidebar's per-navigation remount — otherwise the cache would

// reset every nav and "de-duped per href" would only hold within a single page.

// Bounded by the number of distinct internal hrefs the user hovers/focuses.

const prefetchedHrefs = new Set<string>()

// Brand NavList/Breadcrumbs items render plain <a>s navigated via router.push,

// so Next.js doesn't prefetch their destinations the way next/link would. This

// hook warms a route on hover/focus.

//

// Scope of the benefit here is small on purpose: every article is a

// getServerSideProps route, and router.prefetch only fetches the JS bundle for

// those (not the getServerSideProps data), while page data is already served fast

// from the Fastly edge. All articles also share one [...restPage] bundle, so after

// the first navigation there's usually nothing left to fetch. It still helps the

// first cold visit, and would fetch data too if a route ever moves to

// getStaticProps. router.prefetch is production-only (no prefetch in dev); we

// de-dupe per href so re-entering a link doesn't re-issue.

export function usePrefetchOnInteraction() {

const prefetch = useCallback(async (router: Router, href: string) => {

if (

process.env.NODE_ENV !== 'production' ||

!href.startsWith('/') ||

prefetchedHrefs.has(href)

) {

return

}

prefetchedHrefs.add(href)

try {

// hrefs already include the locale prefix (e.g. /en/...), so disable Next.js

// locale handling to match the router.push calls at the click sites.

await router.prefetch(href, undefined, { locale: false })

} catch {

// A transient chunk/network failure shouldn't permanently suppress retries;

// un-mark so a later hover/focus can try again (mirrors next/link).

prefetchedHrefs.delete(href)

}

}, [])

return prefetch

}