'use client';

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

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

interface ThemeState {
  theme: Theme;
  setTheme: (t: Theme) => void;
}

const ThemeContext = createContext<ThemeState>({
  theme: 'system',
  setTheme: () => {},
});

export function useTheme() {
  return useContext(ThemeContext);
}

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

  useEffect(() => {
    const stored = localStorage.getItem('tracker_theme') as Theme | null;
    if (stored) setThemeState(stored);
  }, []);

  useEffect(() => {
    const root = document.documentElement;
    if (theme === 'dark') {
      root.classList.add('dark');
    } else if (theme === 'light') {
      root.classList.remove('dark');
    } else {
      const prefersDark = window.matchMedia('(prefers-color-scheme: dark)').matches;
      root.classList.toggle('dark', prefersDark);
    }
  }, [theme]);

  const setTheme = (t: Theme) => {
    setThemeState(t);
    localStorage.setItem('tracker_theme', t);
  };

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