const INDEX_DOCUMENT = 'index.html'
const ERROR_DOCUMENT = '404.html'

addEventListener('fetch', event => {
  event.respondWith(handleRequest(event.request))
})

/**
 * @param {Request} request
 */
async function handleRequest(request) {
  const url = new URL(request.url)

  if (url.pathname.endsWith('/')) {
    url.pathname = `${url.pathname}${INDEX_DOCUMENT}`
    request = new Request(url, request)
  }

  let response = await fetch(request)

  if (response.status === 404) {    
    url.pathname = ERROR_DOCUMENT
    request = new Request(url, request)
    response = await fetch(request)

    response = new Response(response.body, {
      status: 404,
      statusText: 'Not Found',
      headers: response.headers
    })      
  } 

  return response
}