/**
 * Stage 04-perf：真实 DOM 操作性能实证（耗时对比版）
 * 动态调整数据量，复杂节点，三种更新策略耗时一目了然
 */

const listEl = document.getElementById("list");
const statsEl = document.getElementById("stats");
const compareDisplay = document.getElementById("compareDisplay");
const rangeN = document.getElementById("rangeN");
const nValueSpan = document.getElementById("nValue");

// ---------- 当前数据量（与滑块同步）----------
let N = 10000;
let items = [];

// 记录最近一次各方案耗时（ms），用于页面展示
const lastResult = {
  innerHTML: "-",
  createElement: "-",
  exact: "-",
};

// ---------- 工具函数：生成初始数据 ----------
function generateItems(count) {
  return Array.from({ length: count }, (_, i) => ({
    id: i,
    title: `Item ${i}`,
    desc: `Description for item ${i}`,
    tag: i % 3 === 0 ? "active" : "inactive",
  }));
}

// ---------- 复杂节点构造 ----------
/**
 * 生成带子元素的 <li>，模拟真实 UI 片段
 * @param {Object} item
 * @returns {HTMLLIElement}
 */
function createComplexItem(item) {
  const li = document.createElement("li");
  li.className = "list-item";

  const avatar = document.createElement("div");
  avatar.className = "avatar";
  avatar.textContent = item.id % 100;

  const content = document.createElement("div");
  content.className = "content";

  const title = document.createElement("h4");
  title.textContent = item.title;

  const desc = document.createElement("p");
  desc.textContent = item.desc;

  const tag = document.createElement("span");
  tag.className = "tag " + item.tag;
  tag.textContent = item.tag;

  content.appendChild(title);
  content.appendChild(desc);
  content.appendChild(tag);
  li.appendChild(avatar);
  li.appendChild(content);
  return li;
}

/**
 * 构建整个列表的 HTML 字符串（innerHTML 方案）
 * @param {Object[]} data
 * @returns {string}
 */
function buildHTML(data) {
  let html = "";
  for (let i = 0; i < data.length; i++) {
    const item = data[i];
    html += `<li class="list-item">
      <div class="avatar">${item.id % 100}</div>
      <div class="content">
        <h4>${item.title}</h4>
        <p>${item.desc}</p>
        <span class="tag ${item.tag}">${item.tag}</span>
      </div>
    </li>`;
  }
  return html;
}

/**
 * 全量 createElement 重建列表
 * @param {Object[]} data
 */
function rebuildWithCreateElement(data) {
  listEl.innerHTML = "";
  for (let i = 0; i < data.length; i++) {
    listEl.appendChild(createComplexItem(data[i]));
  }
}

/**
 * 精确更新单个项目的内容（只改文字）
 * @param {number} index
 * @param {Object} newItem
 */
function updateOneItemExact(index, newItem) {
  const li = listEl.children[index];
  if (!li) return;
  const h4 = li.querySelector("h4");
  if (h4) h4.textContent = newItem.title;
  const p = li.querySelector("p");
  if (p) p.textContent = newItem.desc;
  const span = li.querySelector("span");
  if (span) {
    span.textContent = newItem.tag;
    span.className = "tag " + newItem.tag;
  }
}

// ---------- 更新页面上的耗时对比显示 ----------
function updateCompareDisplay() {
  compareDisplay.innerHTML = `
    最近耗时对比（N = ${N}）<br>
    innerHTML 全量：<b>${lastResult.innerHTML}ms</b> |
    createElement 全量：<b>${lastResult.createElement}ms</b> |
    精确更新：<b>${lastResult.exact}ms</b>
  `;
}

// ---------- 重置列表到当前 N ----------
function resetList() {
  items = generateItems(N);
  console.time(`reset (${N} 项 createElement)`);
  rebuildWithCreateElement(items);
  console.timeEnd(`reset (${N} 项 createElement)`);
  statsEl.textContent = `列表已重置（${N} 项）`;
  // 清空耗时记录
  lastResult.innerHTML = "-";
  lastResult.createElement = "-";
  lastResult.exact = "-";
  updateCompareDisplay();
}

// ---------- 滑块事件 ----------
// 滑块仅更新显示数值，不自动重建
rangeN.addEventListener("input", (e) => {
  N = parseInt(e.target.value, 10);
  nValueSpan.textContent = N;
});

// 点击“应用”按钮才重建列表
document.getElementById("btnApplyN").addEventListener("click", () => {
  resetList();
});

// ---------- 按钮事件 ----------
document.getElementById("btnReset").addEventListener("click", resetList);

document.getElementById("btnFullInnerHTML").addEventListener("click", () => {
  const newItems = items.map((item, i) =>
    i === 5000 ? { ...item, title: "CHANGED" } : item,
  );

  console.time(`innerHTML 全量 (${N} 项)`);
  listEl.innerHTML = buildHTML(newItems);
  console.timeEnd(`innerHTML 全量 (${N} 项)`);

  // 从控制台取不到精确时间，用 performance.now 手动记录
  const start = performance.now();
  listEl.innerHTML = buildHTML(newItems);
  const end = performance.now();
  lastResult.innerHTML = (end - start).toFixed(2);
  items = newItems;
  statsEl.textContent = "innerHTML 更新完成";
  updateCompareDisplay();
});

document.getElementById("btnFullCreate").addEventListener("click", () => {
  const newItems = items.map((item, i) =>
    i === 5000 ? { ...item, title: "CHANGED" } : item,
  );

  const start = performance.now();
  rebuildWithCreateElement(newItems);
  const end = performance.now();
  lastResult.createElement = (end - start).toFixed(2);
  console.log(`createElement 全量耗时: ${lastResult.createElement}ms`);

  items = newItems;
  statsEl.textContent = "createElement 全量完成";
  updateCompareDisplay();
});

document.getElementById("btnExact").addEventListener("click", () => {
  const targetIndex = Math.min(5000, N - 1);
  const newItems = [...items];
  newItems[targetIndex] = { ...newItems[targetIndex], title: "CHANGED" };

  const start = performance.now();
  updateOneItemExact(targetIndex, newItems[targetIndex]);
  const end = performance.now();
  lastResult.exact = (end - start).toFixed(2);
  console.log(`精确更新耗时: ${lastResult.exact}ms`);

  items = newItems;
  statsEl.textContent = "精确更新完成";
  updateCompareDisplay();
});

// ---------- 启动 ----------
resetList();