script.js

/* ============================================
   Henghui Du - Academic Homepage JavaScript
   ============================================ */

// --- Navigation scroll effect ---
const navbar = document.getElementById('navbar');
const navLinks = document.querySelectorAll('.nav-link');
const sections = document.querySelectorAll('section[id]');
const navToggle = document.getElementById('nav-toggle');
const navMenu = document.getElementById('nav-menu');
const backToTop = document.getElementById('backToTop');

// Scroll handler
function onScroll() {
    const scrollY = window.scrollY;

    // Navbar shadow
    if (scrollY > 50) {
        navbar.classList.add('scrolled');
    } else {
        navbar.classList.remove('scrolled');
    }

    // Active nav link
    let current = '';
    sections.forEach(section => {
        const sectionTop = section.offsetTop - 100;
        const sectionHeight = section.offsetHeight;
        if (scrollY >= sectionTop && scrollY < sectionTop + sectionHeight) {
            current = section.getAttribute('id');
        }
    });

    navLinks.forEach(link => {
        link.classList.remove('active');
        if (link.getAttribute('href') === `#${current}`) {
            link.classList.add('active');
        }
    });

    // Back to top
    if (scrollY > 400) {
        backToTop.classList.add('visible');
    } else {
        backToTop.classList.remove('visible');
    }
}

window.addEventListener('scroll', onScroll, { passive: true });

// --- Mobile nav toggle ---
navToggle.addEventListener('click', () => {
    navMenu.classList.toggle('active');
    const spans = navToggle.querySelectorAll('span');
    if (navMenu.classList.contains('active')) {
        spans[0].style.transform = 'rotate(45deg) translate(5px, 5px)';
        spans[1].style.opacity = '0';
        spans[2].style.transform = 'rotate(-45deg) translate(5px, -5px)';
    } else {
        spans[0].style.transform = '';
        spans[1].style.opacity = '';
        spans[2].style.transform = '';
    }
});

// Close mobile nav on link click
navLinks.forEach(link => {
    link.addEventListener('click', () => {
        navMenu.classList.remove('active');
        const spans = navToggle.querySelectorAll('span');
        spans[0].style.transform = '';
        spans[1].style.opacity = '';
        spans[2].style.transform = '';
    });
});

// --- Back to top ---
backToTop.addEventListener('click', () => {
    window.scrollTo({ top: 0, behavior: 'smooth' });
});

// --- Intersection Observer for animations ---
const observerOptions = {
    threshold: 0.1,
    rootMargin: '0px 0px -50px 0px'
};

const observer = new IntersectionObserver((entries) => {
    entries.forEach(entry => {
        if (entry.isIntersecting) {
            entry.target.classList.add('animate-in');
            observer.unobserve(entry.target);
        }
    });
}, observerOptions);

// Observe all section titles and pub items
document.querySelectorAll('.section-title, .pub-item, .timeline-item, .news-item').forEach(el => {
    el.style.opacity = '0';
    el.style.transform = 'translateY(20px)';
    observer.observe(el);
});

// --- Smooth entrance ---
document.addEventListener('DOMContentLoaded', () => {
    document.body.style.opacity = '1';
});

// --- Console greeting ---
console.log('%c🎓 Henghui Du\'s Homepage', 'color: #2563eb; font-size: 16px; font-weight: bold;');
console.log('%cFeel free to explore the source code!', 'color: #64748b; font-size: 12px;');