(function() {
    // 1. 注入样式
    const style = document.createElement('style');
    style.textContent = `
        .scroll-btn {
            position: fixed;
            right: 20px;
            width: 40px;
            height: 40px;
            background-color: rgba(0, 0, 0, 0.7);
            color: white;
            border-radius: 50%;
            border: 2px solid rgba(255, 255, 255, 0.9); /* 增加白色边框 */
            display: flex;
            justify-content: center;
            align-items: center;
            cursor: pointer;
            z-index: 9999;
            box-shadow: 0 4px 12px rgba(0,0,0,0.5); /* 加重阴影 */
            transition: all 0.3s;
            user-select: none;
            -webkit-tap-highlight-color: transparent;
        }

        .scroll-btn:hover {
            background-color: rgba(0, 0, 0, 0.9);
            border-color: #fff;
            transform: scale(1.05);
            box-shadow: 0 6px 16px rgba(0,0,0,0.6);
        }

        .scroll-btn:active {
            transform: scale(0.95);
        }

        /* 箭头基础样式 */
        .scroll-btn::after {
            content: '';
            width: 10px;
            height: 10px;
            border-right: 2px solid white;
            border-bottom: 2px solid white;
        }

        /* 下一页按钮位置和箭头 */
        .next-btn {
            bottom: 20%;
        }
        .next-btn::after {
            transform: rotate(45deg);
            margin-top: -4px;
        }

        /* 上一页按钮位置和箭头 */
        .prev-btn {
            bottom: calc(20% + 55px); /* 40px height + 15px gap */
        }
        .prev-btn::after {
            transform: rotate(-135deg); /* 向上箭头 */
            margin-top: 4px;
        }

        /* 回到顶部按钮 */
        .top-btn {
            bottom: calc(20% + 110px); /* 40px * 2 + 15px * 2 */
            opacity: 0;
            pointer-events: none;
            transition: opacity 0.3s, background-color 0.3s, transform 0.2s;
        }
        .top-btn.visible {
            opacity: 1;
            pointer-events: auto;
        }
        /* 利用 before 画横线，after 画箭头 */
        .top-btn::before {
            content: '';
            position: absolute;
            width: 12px;
            height: 2px;
            background-color: white;
            top: 12px; /* 调整横线位置 */
        }
        .top-btn::after {
            transform: rotate(-135deg);
            margin-top: 2px; /* 调整箭头位置，使其位于横线下方 */
        }

        /* 移动端适配 */
        @media (max-width: 768px) {
            .scroll-btn {
                width: 40px;
                height: 40px;
                right: 15px;
                background-color: rgba(0, 0, 0, 0.5);
            }
            
            .next-btn {
                bottom: 100px;
            }
            
            .prev-btn {
                bottom: 155px; /* 100px + 40px height + 15px gap */
            }

            .top-btn {
                bottom: 218px; /* 163px + 40px height + 15px gap */
            }
            
            .top-btn::before {
                top: 10px; /* 移动端按钮大一点，微调位置 */
            }
        }
    `;
    document.head.appendChild(style);

    // 辅助函数：创建按钮
    function createBtn(className, title) {
        const btn = document.createElement('div');
        btn.className = `scroll-btn ${className}`;
        btn.title = title;
        document.body.appendChild(btn);
        return btn;
    }

    // 2. 创建按钮
    const topBtn = createBtn('top-btn', '回到顶部');
    const prevBtn = createBtn('prev-btn', '上一屏');
    const nextBtn = createBtn('next-btn', '下一屏');

    // 3. 滚动逻辑
    function scrollByViewport(direction) {
        const viewportHeight = window.innerHeight;
        const currentScroll = window.scrollY || window.pageYOffset;
        const targetScroll = currentScroll + (direction * viewportHeight);

        window.scrollTo({
            top: targetScroll,
            behavior: 'smooth'
        });
    }

    // 4. 绑定事件
    nextBtn.addEventListener('click', function() {
        scrollByViewport(1);
    });

    prevBtn.addEventListener('click', function() {
        scrollByViewport(-1);
    });
    
    topBtn.addEventListener('click', function() {
        window.scrollTo({
            top: 0,
            behavior: 'smooth'
        });
    });

    // 5. 监听滚动，控制回到顶部按钮显隐
    function handleScroll() {
        const viewportHeight = window.innerHeight;
        const currentScroll = window.scrollY || window.pageYOffset;
        
        // 当滚动超过一屏时显示
        if (currentScroll >= viewportHeight) {
            topBtn.classList.add('visible');
        } else {
            topBtn.classList.remove('visible');
        }
    }

    // 初始检查一次
    handleScroll();
    
    // 添加监听，使用 passive 提高性能
    window.addEventListener('scroll', handleScroll, { passive: true });

})();