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

export type Theme = 'dark' | 'light';

interface ThemeContextType {
  theme: Theme;
  toggleTheme: () => void;
  setTheme: (theme: Theme) => void;
  isDark: boolean;
  isLight: boolean;
}

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

function getInitialTheme(): Theme {
  if (typeof window === 'undefined') return 'dark';
  const stored = localStorage.getItem('dg-theme') as Theme | null;
  if (stored === 'dark' || stored === 'light') return stored;
  return 'dark';
}

function applyTheme(theme: Theme) {
  document.documentElement.setAttribute('data-theme', theme);
}

export function ThemeProvider({ children }: { children: React.ReactNode }) {
  const [theme, setThemeState] = useState<Theme>(getInitialTheme);

  useEffect(() => {
    applyTheme(theme);
  }, [theme]);

  const toggleTheme = useCallback(() => {
    setThemeState(prev => {
      const next = prev === 'dark' ? 'light' : 'dark';
      localStorage.setItem('dg-theme', next);
      return next;
    });
  }, []);

  const setTheme = useCallback((t: Theme) => {
    localStorage.setItem('dg-theme', t);
    setThemeState(t);
  }, []);

  const value = useMemo(() => ({
    theme,
    toggleTheme,
    setTheme,
    isDark: theme === 'dark',
    isLight: theme === 'light',
  }), [theme, toggleTheme, setTheme]);

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

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