/**
 * Shared state for the registration dialog.
 *
 * `<RegistrationDialog />` is mounted exactly once (app.vue), so every call to action on
 * the site — header, hero, courier band, registration section — drives the same instance.
 * Consequence worth keeping: the form keeps whatever the visitor already typed when the
 * dialog is closed and reopened.
 *
 * …which is exactly why the dialog used to reopen on the "check your inbox" screen after
 * a successful submission: `done` and the form data are per-instance state, and closing
 * the dialog never touched them. `openDialog()` therefore bumps `resetToken`, and
 * RegistrationForm listens for it. The reset happens on OPEN, never on close, so
 * dismissing the dialog halfway through typing still preserves the input.
 *
 * The element that opened the dialog is held in a module-level variable rather than in
 * `useState`, because it is a DOM node (never serialisable into the SSR payload). It is
 * only ever written from a browser event handler.
 */
export type RegistrationPreset = '' | 'klinik' | 'kurierdienst'

let lastTrigger: HTMLElement | null = null

export const useRegistrationDialog = () => {
  const open = useState<boolean>('b24-registration-dialog', () => false)
  const presetType = useState<RegistrationPreset>('b24-registration-preset', () => '')
  /** Incremented on every open; RegistrationForm watches it to clear finished state. */
  const resetToken = useState<number>('b24-registration-reset', () => 0)

  /**
   * Opens the dialog. Pass the click event so focus can be returned to the exact CTA that
   * opened it; pass a preset to skip step 1 for CTAs that already state the type
   * ("Als Kurierdienst registrieren").
   */
  const openDialog = (event?: Event | null, preset: RegistrationPreset = '') => {
    if (import.meta.client) {
      const candidate = (event?.currentTarget ?? document.activeElement) as HTMLElement | null
      lastTrigger = candidate && typeof candidate.focus === 'function' ? candidate : null
    }
    // Assigned unconditionally: a preset left over from an earlier CTA must not leak into
    // an open that deliberately asks for no preselection ("Registrierung starten").
    presetType.value = preset
    resetToken.value++
    open.value = true
  }

  const closeDialog = () => {
    open.value = false
  }

  /** Returns focus to the CTA that opened the dialog (WCAG 2.4.3 "Focus Order"). */
  const restoreTriggerFocus = () => {
    const el = lastTrigger
    lastTrigger = null
    if (!import.meta.client || !el || !document.contains(el)) return
    // One frame later: the dialog is out of the top layer by then, so no scroll fight.
    requestAnimationFrame(() => el.focus())
  }

  return { open, presetType, resetToken, openDialog, closeDialog, restoreTriggerFocus }
}