static/frontend/src/contexts/ThemeContext.tsx

/**
 * Theme Context
 * Manages light/dark theme with localStorage persistence
 */

import { createContext, useContext, useEffect, useState, type ReactNode } from 'react';
import type { Theme } from '@/types';

interface ThemeContextValue {
  theme: Theme;
  toggleTheme: () => void;
  setTheme: (theme: Theme) => void;
}

const ThemeContext = createContext<ThemeContextValue | null>(null);

const STORAGE_KEY = 'theme';

export function ThemeProvider({ children }: { children: ReactNode }) {
  const [theme, setThemeState] = useState<Theme>(() => {
    // Check localStorage first
    const stored = localStorage.getItem(STORAGE_KEY) as Theme | null;
    if (stored === 'light' || stored === 'dark') return stored;
    
    // Check system preference
    if (window.matchMedia('(prefers-color-scheme: light)').matches) {
      return 'light';
    }
    return 'dark';
  });

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

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

  const setTheme = (newTheme: Theme) => {
    setThemeState(newTheme);
  };

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

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