rxminder/hooks/useTheme.ts

import { useEffect, useMemo } from 'react';
import { useLocalStorage } from './useLocalStorage';

type Theme = 'light' | 'dark' | 'system';

export function useTheme() {
  const [theme, setTheme] = useLocalStorage<Theme>('theme', 'system');

  const systemTheme = useMemo(() => {
    if (typeof window !== 'undefined' && window.matchMedia) {
      return window.matchMedia('(prefers-color-scheme: dark)').matches
        ? 'dark'
        : 'light';
    }
    return 'light';
  }, []);

  const applyTheme = () => {
    const themeToApply = theme === 'system' ? systemTheme : theme;
    const root = window.document.documentElement;
    root.classList.remove('light', 'dark');
    root.classList.add(themeToApply);
  };

  useEffect(() => {
    const mediaQuery = window.matchMedia('(prefers-color-scheme: dark)');
    const handleChange = () => {
      if (theme === 'system') {
        applyTheme();
      }
    };
    mediaQuery.addEventListener('change', handleChange);
    return () => mediaQuery.removeEventListener('change', handleChange);
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [theme]);

  useEffect(() => {
    applyTheme();
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [theme, systemTheme]);

  return { theme, setTheme };
}