'use client';

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

type Theme = 'light' | 'dark';

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

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

function getInitialTheme(): Theme {
  if (typeof window === 'undefined') return 'light'; // SSR guard
  const stored = localStorage.getItem('theme') as Theme | null;
  if (stored) return stored;
  return window.matchMedia('(prefers-color-scheme: dark)').matches ? 'dark' : 'light';
}

function applyTheme(theme: Theme) {
  document.documentElement.classList.toggle('dark', theme === 'dark');
}

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

  // Sync the DOM class whenever theme changes — no setState here
  useEffect(() => {
    applyTheme(theme);
  }, [theme]);

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

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

  return (
    <ThemeContext.Provider value={{ theme, toggleTheme, setTheme }}>
      {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;
}