import * as React from 'react';

/**
 * Puts the kit's dark mode on the document, which is the only way it turns on.
 *
 * `globals.css` declares `@custom-variant dark (&:where(.dark, .dark *))`, so
 * `dark:` utilities key off a **class on an ancestor**, not off
 * `prefers-color-scheme`. Nothing in `dist/` toggles it: a consuming app owns
 * that switch, and this is the two lines such an app writes.
 *
 * Shared because the kit has two doc surfaces that each need it — the showcase's
 * `?theme=` parameter and Storybook's theme toolbar — and a copy in each meant
 * the mechanism was documented twice and could be corrected once. It lives on
 * the showcase side of the line on purpose: `.storybook/` is what a scaffold can
 * be generated without, the showcase always ships.
 */
export function useThemeClass(theme: 'light' | 'dark' | string) {
  React.useEffect(() => {
    document.documentElement.classList.toggle('dark', theme === 'dark');
  }, [theme]);
}