task-manager/client/src/components/ThemeToggle.tsx

import { useState, useEffect } from 'react';
import { Button } from '@/components/ui/button';
import { Moon, Sun } from 'lucide-react';
import { useTranslation } from 'react-i18next';

export default function ThemeToggle() {
  const { t } = useTranslation();
  const [isDark, setIsDark] = useState(false);

  useEffect(() => {
    // Check for saved theme preference or default to light mode
    const savedTheme = localStorage.getItem('theme');
    const prefersDark = window.matchMedia('(prefers-color-scheme: dark)').matches;

    const shouldBeDark = savedTheme === 'dark' || (!savedTheme && prefersDark);
    setIsDark(shouldBeDark);

    // Apply theme to document
    if (shouldBeDark) {
      document.documentElement.classList.add('dark');
    } else {
      document.documentElement.classList.remove('dark');
    }
  }, []);

  const toggleTheme = () => {
    const newTheme = !isDark;
    setIsDark(newTheme);

    if (newTheme) {
      document.documentElement.classList.add('dark');
      localStorage.setItem('theme', 'dark');
    } else {
      document.documentElement.classList.remove('dark');
      localStorage.setItem('theme', 'light');
    }
  };

  return (
    <Button
      variant="outline"
      size="icon"
      onClick={toggleTheme}
      className="w-10 h-10 rounded-full border-2 border-primary/20 hover:border-primary hover:bg-primary/10 transition-all duration-300"
      title={t('app.toggleTheme')}
    >
      {isDark ? (
        <Moon className="h-5 w-5 text-violet-500 transition-all" />
      ) : (
        <Sun className="h-5 w-5 text-orange-500 transition-all" />
      )}
      <span className="sr-only">{isDark ? t('theme.dark') : t('theme.light')}</span>
    </Button>
  );
}