// 山东大学公共卫生学科100周年庆典网站 - JavaScript

// 轮播图功能
let currentSlide = 0;
const slides = document.querySelectorAll('.carousel-item');

function showSlide(index) {
    // 隐藏所有幻灯片
    slides.forEach(slide => slide.classList.remove('active'));
    
    // 显示指定幻灯片
    if (index >= slides.length) {
        currentSlide = 0;
    } else if (index < 0) {
        currentSlide = slides.length - 1;
    } else {
        currentSlide = index;
    }
    
    slides[currentSlide].classList.add('active');
}

function changeSlide(direction) {
    showSlide(currentSlide + direction);
}

function syncNoticeListHeight() {
    const carouselElement = document.querySelector('.carousel');
    const noticeListElement = document.querySelector('.notice-list');
    if (!carouselElement || !noticeListElement) {
        return;
    }

    if (window.innerWidth <= 768) {
        noticeListElement.style.maxHeight = 'none';
        return;
    }

    noticeListElement.style.maxHeight = `${carouselElement.offsetHeight}px`;
}

// 自动轮播（每5秒切换一次）
let autoSlideInterval = setInterval(() => {
    changeSlide(1);
}, 5000);

// 鼠标悬停时暂停自动轮播
const carousel = document.querySelector('.carousel');
if (carousel) {
    carousel.addEventListener('mouseenter', () => {
        clearInterval(autoSlideInterval);
    });
    
    carousel.addEventListener('mouseleave', () => {
        autoSlideInterval = setInterval(() => {
            changeSlide(1);
        }, 5000);
    });
}

// 页面加载完成后初始化、绑定动画与平滑滚动
document.addEventListener('DOMContentLoaded', () => {
    if (slides.length > 0) {
        showSlide(0);
    }

    syncNoticeListHeight();
    window.addEventListener('resize', syncNoticeListHeight);

    const banner = document.querySelector('.banner');
    const nav = document.querySelector('.main-nav');
    
    // 防止点击导航后滚动监听器覆盖 active 状态
    let isClickScrolling = false;
    let clickScrollTimer = null;
    let isPageSnapping = false;

    function setScrollLock(duration = 1000) {
        isClickScrolling = true;
        isPageSnapping = true;
        clearTimeout(clickScrollTimer);

        clickScrollTimer = setTimeout(() => {
            isClickScrolling = false;
            isPageSnapping = false;
        }, duration);
    }

    function scrollToPosition(top) {
        setScrollLock();
        window.scrollTo({
            top,
            behavior: 'smooth'
        });
    }

    function scrollToSecondPage() {
        if (!nav) {
            return;
        }

        scrollToPosition(nav.offsetTop);
    }

    function scrollToBanner() {
        scrollToPosition(0);
    }

    if (banner && nav) {
        window.addEventListener('wheel', (event) => {
            if (isPageSnapping) {
                event.preventDefault();
                return;
            }

            const scrollY = window.scrollY;
            const bannerThreshold = banner.offsetHeight - 40;
            const snapBackThreshold = banner.offsetHeight * 1.5;

            if (event.deltaY > 0 && scrollY < bannerThreshold) {
                event.preventDefault();
                scrollToSecondPage();
            } else if (event.deltaY < 0 && scrollY < snapBackThreshold && scrollY > 0) {
                event.preventDefault();
                setScrollLock(500);
                window.scrollTo({
                    top: 0,
                    behavior: 'smooth'
                });
            }
        }, { passive: false });
    }
    
    // 1. 导航栏平滑滚动及高亮更新
    document.querySelectorAll('a[href^="#"]').forEach(anchor => {
        anchor.addEventListener('click', function (e) {
            e.preventDefault();
            const targetId = this.getAttribute('href');
            if(targetId === '#') return;
            
            const targetElement = document.querySelector(targetId);
            if (targetElement) {
                // 减去导航栏高度(约75px)，防止导航栏遮挡标题
                const headerOffset = 75;
                const elementPosition = targetElement.getBoundingClientRect().top;
                const offsetPosition = elementPosition + window.pageYOffset - headerOffset;

                // 设置点击滚动标记
                window.scrollTo({
                    top: offsetPosition,
                    behavior: "smooth"
                });
                setScrollLock();
                
                // 立即更新活动状态
                document.querySelectorAll('.nav-link').forEach(link => {
                    link.classList.remove('active');
                });
                this.classList.add('active');
            }
        });
    });

    // 2. 元素入场动画 (Intersection Observer)
    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('visible');
                observer.unobserve(entry.target); 
            }
        });
    }, observerOptions);

    document.querySelectorAll('.scroll-animate').forEach(el => {
        observer.observe(el);
    });

    // 3. 页面滚动时自动高亮当前所在导航
    const sections = document.querySelectorAll('section');
    const navLinks = document.querySelectorAll('.nav-link');

    window.addEventListener('scroll', () => {
        // 如果是点击导航触发的滚动，不执行自动更新
        if (isClickScrolling) {
            return;
        }
        
        let current = '';
        const scrollY = window.scrollY;
        
        // 只有滚动超过banner区域（约100vh）后才开始高亮导航
        if (scrollY < window.innerHeight * 0.8) {
            // 在顶部banner区域时，取消所有active状态
            navLinks.forEach(link => {
                link.classList.remove('active');
            });
            return;
        }

        sections.forEach(section => {
            const sectionTop = section.offsetTop;
            const sectionHeight = section.offsetHeight;
            // 更精确的判断：当前滚动位置在该区域范围内
            if (scrollY >= (sectionTop - 200) && scrollY < (sectionTop + sectionHeight - 200)) {
                current = section.getAttribute('id');
            }
        });

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