import { useEffect } from 'react'
import { useLocation } from 'react-router-dom'

export default function ScrollToTop() {
  const { pathname, hash } = useLocation()

  // Cross-page navigation: scroll to hash or top on route change.
  //
  // getElementById, not querySelector. querySelector THROWS on a fragment that
  // is not a valid CSS selector, and an id starting with a digit is not one:
  // `#8x8-implementation` and even `/#1` would throw here, in an effect inside
  // the root route, and the error boundary would replace the header, the page
  // and the footer with the error screen. The long-form service pages exist to
  // be deep-linked from search results and AI answers, so a link nobody here
  // wrote must never be able to blank the page. An unknown id scrolls to top.
  useEffect(() => {
    if (hash.length > 1) {
      let el = null
      try {
        el = document.getElementById(decodeURIComponent(hash.slice(1)))
      } catch {
        el = null // a fragment that is not valid percent-encoding
      }
      if (el) {
        el.scrollIntoView({ behavior: 'smooth' })
        return
      }
    }
    window.scrollTo(0, 0)
  }, [pathname, hash])

  // Same-page: React Router won't re-navigate if URL is already identical,
  // so intercept clicks on any link pointing to #contact-form directly.
  useEffect(() => {
    const handleClick = (e) => {
      const anchor = e.target.closest('a')
      if (!anchor) return
      const href = anchor.getAttribute('href') || ''
      if (!href.includes('#contact-form')) return
      const el = document.querySelector('#contact-form')
      if (!el) return
      e.preventDefault()
      el.scrollIntoView({ behavior: 'smooth' })
      window.history.pushState(null, '', '#contact-form')
    }
    document.addEventListener('click', handleClick)
    return () => document.removeEventListener('click', handleClick)
  }, [])

  return null
}