(() => {
    const root = document.documentElement;
    const preferredTheme = () => localStorage.getItem('uniformflow-theme')
        || (window.matchMedia('(prefers-color-scheme: dark)').matches ? 'dark' : 'light');

    const applyTheme = theme => {
        root.dataset.theme = theme;
        localStorage.setItem('uniformflow-theme', theme);
        document.querySelectorAll('[data-theme-toggle]').forEach(button => {
            const nextTheme = theme === 'dark' ? 'light' : 'dark';
            button.setAttribute('aria-label', `Switch to ${nextTheme} theme`);
            button.setAttribute('title', `Switch to ${nextTheme} theme`);
            button.setAttribute('aria-pressed', theme === 'dark' ? 'true' : 'false');
        });
    };

    applyTheme(root.dataset.theme || preferredTheme());
    document.addEventListener('DOMContentLoaded', () => {
        applyTheme(root.dataset.theme || preferredTheme());
        document.querySelectorAll('[data-theme-toggle]').forEach(button => button.addEventListener('click', () => {
            const nextTheme = root.dataset.theme === 'dark' ? 'light' : 'dark';
            const reducedMotion = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

            if (reducedMotion) {
                applyTheme(nextTheme);
                return;
            }

            root.classList.add('theme-changing');
            if (document.startViewTransition) {
                document.startViewTransition(() => applyTheme(nextTheme)).finished.finally(() => {
                    window.setTimeout(() => root.classList.remove('theme-changing'), 120);
                });
            } else {
                requestAnimationFrame(() => applyTheme(nextTheme));
                window.setTimeout(() => root.classList.remove('theme-changing'), 420);
            }
        }));
    });
})();