/**
 * "Save as PDF" through the browser's print dialog. While printing (also with ⌘ P) the page title is `fileName`, which
 * browsers name the PDF after, and dark mode is off, so the PDF is dark text on white.
 */
export function usePdfExport(fileName: MaybeRefOrGetter<string>, onBeforePrint?: () => void) {
  // What to restore after printing; null while not printing. Browsers can fire beforeprint twice before afterprint.
  let screen: { title: string, dark: boolean } | null = null

  function beforePrint() {
    onBeforePrint?.()
    if (screen) return
    screen = { title: document.title, dark: document.documentElement.classList.contains('dark') }
    document.title = toValue(fileName)
    document.documentElement.classList.remove('dark')
  }

  function afterPrint() {
    if (!screen) return
    document.title = screen.title
    if (screen.dark) document.documentElement.classList.add('dark')
    screen = null
  }

  onMounted(() => {
    window.addEventListener('beforeprint', beforePrint)
    window.addEventListener('afterprint', afterPrint)
  })
  onBeforeUnmount(() => {
    window.removeEventListener('beforeprint', beforePrint)
    window.removeEventListener('afterprint', afterPrint)
  })

  // Opens the browser's print dialog, which offers "Save as PDF"
  return { savePdf: () => window.print() }
}