frontend/src/contexts/ThemeContext.js

import { createContext, useContext, useState, useEffect } from 'react';

const ThemeContext = createContext();

export function ThemeProvider({ children }) {
  const [theme, setTheme] = useState(() => {
    return localStorage.getItem('llm-compare-theme') || 'light';
  });

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

  const toggleTheme = () => setTheme(t => t === 'light' ? 'dark' : 'light');

  return (
    <ThemeContext.Provider value={{ theme, toggleTheme, isLight: theme === 'light', isDark: theme === 'dark' }}>
      {children}
    </ThemeContext.Provider>
  );
}

export const useTheme = () => useContext(ThemeContext);