Stop_smoking_website_ver2/src/lib/theme-context.tsx

'use client';

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

type Theme = 'dark' | 'light';

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

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

export function ThemeProvider({ children }: { children: ReactNode }) {
  const [theme, setTheme] = useState<Theme>('dark');

  useEffect(() => {
    // Check localStorage first
    const saved = localStorage.getItem('theme') as Theme | null;
    if (saved) {
      setTheme(saved);
      return;
    }

    // Fall back to system preference
    const prefersDark = window.matchMedia('(prefers-color-scheme: dark)').matches;
    setTheme(prefersDark ? 'dark' : 'light');
  }, []);

  // Listen for system preference changes (only if no manual preference set)
  useEffect(() => {
    const mediaQuery = window.matchMedia('(prefers-color-scheme: dark)');

    const handleChange = (e: MediaQueryListEvent) => {
      // Only update if user hasn't manually set a preference
      if (!localStorage.getItem('theme')) {
        setTheme(e.matches ? 'dark' : 'light');
      }
    };

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

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

  const toggleTheme = () => {
    const newTheme = theme === 'dark' ? 'light' : 'dark';
    setTheme(newTheme);
    localStorage.setItem('theme', newTheme);
  };

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

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