// ==UserScript==
// @name         DeepSeek一键回顶
// @namespace    https://scriptcat.org/zh-CN/users/214553
// @version      1.1.0
// @description  在DeepSeek网页上添加「回到顶部」按钮，一键回到对话的最开始。
// @author       English3（Σπg|!εh๑๑๑）
// @license      MIT
// @icon         https://deepseek.com/favicon.ico
// @match        https://chat.deepseek.com/*
// @run-at       document-idle
// @grant        none
// ==/UserScript==

(() => {
  'use strict';
  const ID = 'ds-back-top-v4';

  const goTop = () => {
    try {
      // 找到所有可能的主滚动容器
      let bestEl = null;
      let maxScrollHeight = 0;
      
      document.querySelectorAll('div, main, section').forEach(el => {
        const style = window.getComputedStyle(el);
        if ((style.overflowY === 'auto' || style.overflowY === 'scroll') && el.scrollHeight > maxScrollHeight && el.clientHeight > 100) {
          maxScrollHeight = el.scrollHeight;
          bestEl = el;
        }
      });

      if (bestEl) {
        // 聚焦该容器，确保键盘事件能作用在这里
        bestEl.setAttribute('tabindex', '-1');
        bestEl.focus();

        // 模拟按下 Home 键，触发虚拟滚动加载最早期内容
        const homeEvent = new KeyboardEvent('keydown', {
          key: 'Home',
          code: 'Home',
          keyCode: 36,
          which: 36,
          bubbles: true,
          cancelable: true
        });
        bestEl.dispatchEvent(homeEvent);

        // 强制无缝滚动到顶
        setTimeout(() => {
          bestEl.scrollTo({ top: 0, behavior: 'smooth' });
        }, 50);
      } else {
        // 全局兜底
        window.scrollTo({ top: 0, behavior: 'smooth' });
        document.documentElement.scrollTop = 0;
      }
    } catch (e) {
      console.warn('DeepSeek回顶脚本执行异常:', e);
    }
  };

  // 创建悬浮按钮
  const btn = document.createElement('button');
  btn.id = ID;
  btn.type = 'button';
  btn.title = '回到最早的对话';
  btn.setAttribute('aria-label', '回到最早的对话');
  btn.innerHTML = `
    <svg width="24" height="24" viewBox="0 0 24 24" fill="none"
      stroke="currentColor" stroke-width="2.5" stroke-linecap="round" stroke-linejoin="round">
      <path d="M12 19V5M5 12l7-7 7 7"/>
    </svg>
  `;

  // 强制固定悬浮样式，使用最高层级防遮挡
  Object.assign(btn.style, {
    position: 'fixed',
    right: '20px',
    bottom: '100px',
    width: '48px',
    height: '48px',
    borderRadius: '50%',
    background: 'rgba(0, 0, 0, 0.7)',
    color: '#ffffff',
    border: '2px solid rgba(255, 255, 255, 0.2)',
    display: 'flex',
    alignItems: 'center',
    justifyContent: 'center',
    cursor: 'pointer',
    zIndex: '9999999',
    boxShadow: '0 4px 15px rgba(0,0,0,0.4)',
    opacity: '0.8',
    transition: 'all 0.2s ease',
    padding: '0',
    margin: '0'
  });

  // 悬浮动画
  btn.onmouseenter = () => { btn.style.opacity = '1'; btn.style.transform = 'scale(1.1)'; btn.style.background = 'rgba(0, 0, 0, 0.9)'; };
  btn.onmouseleave = () => { btn.style.opacity = '0.8'; btn.style.transform = 'scale(1)'; btn.style.background = 'rgba(0, 0, 0, 0.7)'; };
  
  // 点击事件
  btn.addEventListener('click', (e) => {
    e.preventDefault();
    e.stopPropagation();
    goTop();
  });

  // 核心防丢失机制：定时检查并挂载
  const ensureMount = () => {
    if (!document.body) return;
    if (!document.getElementById(ID)) {
      document.body.appendChild(btn);
    }
  };

  // 初始挂载
  ensureMount();

  // 使用定时器，每 1.5 秒检查一次按钮是否存活，彻底防止被页面重绘消失
  setInterval(ensureMount, 1500);
  
  // 延迟挂载，应对页面初始加载慢
  setTimeout(ensureMount, 500);
  setTimeout(ensureMount, 2000);
})();