frontend/contexts/ThemeContext.tsx

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

interface ThemeContextType {
  theme: 'light' | 'dark';
  toggleTheme: () => void;
}

const ThemeContext = createContext<ThemeContextType | undefined>(undefined);

export function ThemeProvider({ children }: { children: ReactNode }) {
  const [theme, setTheme] = useState<'light' | 'dark'>('light');

  useEffect(() => {
    // Check user preference from localStorage or system preference
    const savedTheme = localStorage.getItem('theme') as 'light' | 'dark' | null;
    const systemPrefersDark = window.matchMedia('(prefers-color-scheme: dark)').matches;

    if (savedTheme) {
      setTheme(savedTheme);
    } else if (systemPrefersDark) {
      setTheme('dark');
    }
  }, []);

  useEffect(() => {
    // Apply theme to document
    document.documentElement.classList.remove('light', 'dark');
    document.documentElement.classList.add(theme);
    localStorage.setItem('theme', theme);
  }, [theme]);

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

  return (
    <ThemeContext.Provider value={{ theme, toggleTheme }}>
      {children}
    </ThemeContext.Provider>
  );
}

export function useTheme() {
  const context = useContext(ThemeContext);
  if (context === undefined) {
    throw new Error('useTheme must be used within a ThemeProvider');
  }
  return context;
}