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

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

interface ThemeContextType {
  theme: Theme;
  setTheme: (theme: Theme) => void;
  resolvedTheme: 'light' | 'dark';
}

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

const STORAGE_KEY = 'hackathon-theme';

function getSystemTheme(): 'light' | 'dark' {
  if (typeof window !== 'undefined') {
    return window.matchMedia('(prefers-color-scheme: dark)').matches ? 'dark' : 'light';
  }
  return 'light';
}

interface ThemeProviderProps {
  children: ReactNode;
  defaultTheme?: Theme;
}

export const ThemeProvider: FC<ThemeProviderProps> = ({ children, defaultTheme = 'system' }) => {
  const [theme, setThemeState] = useState<Theme>(() => {
    if (typeof window !== 'undefined') {
      const stored = localStorage.getItem(STORAGE_KEY) as Theme | null;
      return stored || defaultTheme;
    }
    return defaultTheme;
  });

  const [resolvedTheme, setResolvedTheme] = useState<'light' | 'dark'>(() => {
    if (theme === 'system') {
      return getSystemTheme();
    }
    return theme;
  });

  const setTheme = (newTheme: Theme) => {
    setThemeState(newTheme);
    localStorage.setItem(STORAGE_KEY, newTheme);
  };

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

    const resolved = theme === 'system' ? getSystemTheme() : theme;
    setResolvedTheme(resolved);

    if (resolved === 'dark') {
      root.classList.add('dark');
    } else {
      root.classList.remove('dark');
    }
  }, [theme]);

  useEffect(() => {
    if (theme !== 'system') return;

    const mediaQuery = window.matchMedia('(prefers-color-scheme: dark)');

    const handleChange = (e: MediaQueryListEvent) => {
      const newTheme = e.matches ? 'dark' : 'light';
      setResolvedTheme(newTheme);

      const root = document.documentElement;
      if (newTheme === 'dark') {
        root.classList.add('dark');
      } else {
        root.classList.remove('dark');
      }
    };

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

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

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

export default ThemeProvider;
