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

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

type ThemeProviderProps = {
  children: React.ReactNode;
  defaultTheme?: Theme;
  storageKey?: string;
};

type ThemeProviderState = {
  theme: Theme;
  setTheme: (theme: Theme) => void;
};

const initialState: ThemeProviderState = {
  theme: 'system',
  setTheme: () => null,
};

const ThemeContext = createContext<ThemeProviderState>(initialState);

export function ThemeProvider({
  children,
  defaultTheme = 'system',
  storageKey = 'vite-ui-theme',
}: ThemeProviderProps) {
  const [theme, setTheme] = useState<Theme>(
    () => (localStorage.getItem(storageKey) as Theme) || defaultTheme
  );

  useEffect(() => {
    const root = window.document.documentElement;

    root.classList.remove('light', 'dark');

    if (theme === 'system') {
      const systemTheme = window.matchMedia('(prefers-color-scheme: dark)')
        .matches
        ? 'dark'
        : 'light';

      root.classList.add(systemTheme);
      return;
    }

    root.classList.add(theme);
  }, [theme]);

  // Listen for system changes when theme is 'system'
  useEffect(() => {
    if (theme !== 'system') return;

    const mediaQuery = window.matchMedia('(prefers-color-scheme: dark)');
    
    const handleChange = () => {
      const root = window.document.documentElement;
      if (mediaQuery.matches) {
        root.classList.add('dark');
        root.classList.remove('light');
      } else {
        root.classList.add('light');
        root.classList.remove('dark');
      }
    };

    mediaQuery.addEventListener('change', handleChange);
    return () => mediaQuery.removeEventListener('change', handleChange);
  }, [theme]);

  const value = {
    theme,
    setTheme: (theme: Theme) => {
      localStorage.setItem(storageKey, theme);
      setTheme(theme);
    },
  };

  return (
    <ThemeContext.Provider value={value} {...{ value }}>
      {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;
};
