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

type Theme = 'light' | 'dark';

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

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

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

  useEffect(() => {
    const root = window.document.documentElement;
    root.classList.remove('light', 'dark');
    root.classList.add(theme);
    localStorage.setItem('theme', theme);
  }, [theme]);

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

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

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