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

type Theme = 'light' | 'dark';

const ThemeContext = createContext<{
  theme: Theme;
  toggleTheme: () => void;
}>({ theme: 'dark', toggleTheme: () => {} });

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

  useEffect(() => {
    document.documentElement.classList.toggle('dark', theme === 'dark');
    localStorage.setItem('theme', theme);
  }, [theme]);

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

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

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