frontend/src/hooks/useTheme.ts

import { useState, useEffect, useCallback } from 'react';
import type { Theme } from '../types';

export function useTheme() {
  const [theme, setTheme] = useState<Theme>(() => {
    const stored = localStorage.getItem('theme') as Theme | null;
    if (stored) return stored;
    return window.matchMedia('(prefers-color-scheme: dark)').matches ? 'dark' : 'light';
  });

  useEffect(() => {
    document.documentElement.setAttribute('data-theme', theme);
    localStorage.setItem('theme', theme);
  }, [theme]);

  const toggleTheme = useCallback(() => {
    setTheme((prev) => (prev === 'dark' ? 'light' : 'dark'));
  }, []);

  return { theme, toggleTheme };
}