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

type Theme = 'light' | 'dark';

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

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

const STORAGE_KEY = 'queneva-theme';

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

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

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

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

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