// 返回顶部按钮组件
(function() {
    // 创建返回顶部按钮HTML
    function createBackToTopButton() {
        const button = document.createElement('div');
        button.id = 'back-to-top';
        button.className = 'fixed bottom-8 right-8 z-40 opacity-0 pointer-events-none transition-all duration-300';
        button.innerHTML = `
            <button class="back-to-top-btn group relative w-12 h-12 bg-gradient-to-br from-emerald-400 to-blue-500 rounded-full shadow-lg hover:shadow-xl transform hover:scale-110 transition-all duration-300">
                <span class="absolute inset-0 rounded-full bg-white opacity-0 group-hover:opacity-10 transition-opacity duration-300"></span>
                <svg class="w-6 h-6 text-white absolute top-1/2 left-1/2 transform -translate-x-1/2 -translate-y-1/2" 
                     fill="none" stroke="currentColor" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg">
                    <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M5 10l7-7m0 0l7 7m-7-7v18"></path>
                </svg>
                <span class="absolute -top-10 left-1/2 transform -translate-x-1/2 bg-gray-800 text-white text-xs px-2 py-1 rounded opacity-0 group-hover:opacity-100 transition-opacity duration-300 whitespace-nowrap">
                    返回顶部
                </span>
            </button>
        `;
        document.body.appendChild(button);
        return button;
    }

    // 添加样式
    function addStyles() {
        const style = document.createElement('style');
        style.textContent = `
            #back-to-top.show {
                opacity: 1;
                pointer-events: auto;
                transform: translateY(0);
            }
            
            #back-to-top:not(.show) {
                transform: translateY(100px);
            }
            
            .back-to-top-btn {
                position: relative;
                overflow: hidden;
            }
            
            .back-to-top-btn::before {
                content: '';
                position: absolute;
                top: 0;
                left: -100%;
                width: 100%;
                height: 100%;
                background: linear-gradient(90deg, transparent, rgba(255,255,255,0.2), transparent);
                transition: left 0.5s;
            }
            
            .back-to-top-btn:hover::before {
                left: 100%;
            }
            
            .back-to-top-btn svg {
                animation: float 2s ease-in-out infinite;
            }
            
            @keyframes float {
                0%, 100% {
                    transform: translateX(-50%) translateY(-50%);
                }
                50% {
                    transform: translateX(-50%) translateY(calc(-50% - 3px));
                }
            }
            
            /* 移动端适配 */
            @media (max-width: 768px) {
                #back-to-top {
                    bottom: 1.5rem;
                    right: 1.5rem;
                }
                
                .back-to-top-btn {
                    width: 2.5rem;
                    height: 2.5rem;
                }
                
                .back-to-top-btn svg {
                    width: 1.25rem;
                    height: 1.25rem;
                }
            }
            
            /* 平滑滚动行为 */
            html {
                scroll-behavior: smooth;
            }
            
            /* 防止按钮与其他元素冲突 */
            @media (max-width: 640px) {
                #back-to-top {
                    bottom: 5rem; /* 避免与移动端菜单按钮重叠 */
                }
            }
        `;
        document.head.appendChild(style);
    }

    // 滚动到顶部功能
    function scrollToTop() {
        // 使用 smooth 滚动
        window.scrollTo({
            top: 0,
            behavior: 'smooth'
        });
        
        // 可选：添加动画反馈
        const button = document.querySelector('.back-to-top-btn');
        if (button) {
            button.style.transform = 'scale(0.9)';
            setTimeout(() => {
                button.style.transform = '';
            }, 200);
        }
    }

    // 控制按钮显示/隐藏
    function handleScroll() {
        const button = document.getElementById('back-to-top');
        const scrollTop = window.pageYOffset || document.documentElement.scrollTop;
        const windowHeight = window.innerHeight;
        
        // 当滚动超过一屏高度时显示按钮
        if (scrollTop > windowHeight * 0.5) {
            button.classList.add('show');
        } else {
            button.classList.remove('show');
        }
        
        // 可选：根据滚动位置调整按钮透明度
        if (scrollTop > windowHeight) {
            const maxScroll = document.documentElement.scrollHeight - windowHeight;
            const scrollProgress = Math.min(scrollTop / maxScroll, 1);
            const opacity = 0.5 + scrollProgress * 0.5; // 从50%到100%透明度
            button.style.opacity = button.classList.contains('show') ? opacity : 0;
        }
    }

    // 初始化
    function init() {
        // 添加样式
        addStyles();
        
        // 创建按钮
        const button = createBackToTopButton();
        
        // 添加点击事件
        button.addEventListener('click', scrollToTop);
        
        // 添加滚动监听（使用节流）
        let scrollTimer;
        window.addEventListener('scroll', () => {
            if (scrollTimer) {
                clearTimeout(scrollTimer);
            }
            scrollTimer = setTimeout(handleScroll, 50);
        });
        
        // 初始检查
        handleScroll();
        
        // 键盘快捷键支持（按 'T' 键返回顶部）
        document.addEventListener('keydown', (e) => {
            // 排除输入框等元素
            if (e.target.tagName === 'INPUT' || e.target.tagName === 'TEXTAREA') {
                return;
            }
            
            // 按 T 键或 Home 键返回顶部
            if (e.key === 't' || e.key === 'T' || e.key === 'Home') {
                e.preventDefault();
                scrollToTop();
            }
        });
    }

    // DOM加载完成后初始化
    if (document.readyState === 'loading') {
        document.addEventListener('DOMContentLoaded', init);
    } else {
        init();
    }
})();