import Link from 'next/link'
import { ComponentProps, forwardRef, useRef } from 'react'

type LinkProps = ComponentProps<typeof Link>

export interface PrefetchableLinkProps extends Omit<LinkProps, 'onMouseEnter' | 'onMouseLeave'> {
  prefetcher: () => void
}

const DELAY = 75

const PrefetchableLink = forwardRef<HTMLAnchorElement, PrefetchableLinkProps>(
  function PrefetchableLink({ prefetcher, children, ...props }, ref) {
    const mouseOverStartRef = useRef<number | null>(null)
    const prefetchTimeoutRef = useRef<number | null>(null)

    function onPrefetch() {
      const now = Date.now()

      // setTimeout is not guaranteed to be precise, so we need to check the time again
      if (mouseOverStartRef.current && now - mouseOverStartRef.current >= DELAY) {
        prefetcher()
      }
    }

    function onMouseEnter() {
      mouseOverStartRef.current = Date.now()
      prefetchTimeoutRef.current = window.setTimeout(onPrefetch, DELAY)
    }

    function onMouseLeave() {
      mouseOverStartRef.current = null
      if (prefetchTimeoutRef.current) {
        clearTimeout(prefetchTimeoutRef.current)
        prefetchTimeoutRef.current = null
      }
    }

    return (
      <Link ref={ref} {...props} onMouseEnter={onMouseEnter} onMouseLeave={onMouseLeave}>
        {children}
      </Link>
    )
  }
)

export default PrefetchableLink