const messagesEl = document.getElementById("messages");
const inputEl = document.getElementById("input");
const sendBtn = document.getElementById("sendBtn");
const newChatBtn = document.getElementById("newChatBtn");
const chatListEl = document.getElementById("chatList");
const clearBtn = document.getElementById("clearBtn");

const sidebarToggleBtn = document.getElementById("sidebarToggle");
const appRootEl = document.querySelector(".app");

let chats = JSON.parse(localStorage.getItem("ds_chats") || "{}");
let currentChatId = localStorage.getItem("ds_current_chat");
let sidebarHidden = localStorage.getItem("ds_sidebar_hidden") === "1";

/** ---------- 时间格式化 ---------- */
function formatChatDate(ts) {
  try {
    return new Intl.DateTimeFormat("zh-CN", {
      year: "numeric",
      month: "2-digit",
      day: "2-digit",
    }).format(new Date(ts));
  } catch {
    const d = new Date(ts);
    const y = d.getFullYear();
    const m = String(d.getMonth() + 1).padStart(2, "0");
    const day = String(d.getDate()).padStart(2, "0");
    return `${y}-${m}-${day}`;
  }
}

function formatMsgDateTime(ts) {
  try {
    return new Intl.DateTimeFormat("zh-CN", {
      year: "numeric",
      month: "2-digit",
      day: "2-digit",
      hour: "2-digit",
      minute: "2-digit",
      second: "2-digit",
    }).format(new Date(ts));
  } catch {
    const d = new Date(ts);
    const y = d.getFullYear();
    const m = String(d.getMonth() + 1).padStart(2, "0");
    const day = String(d.getDate()).padStart(2, "0");
    const hh = String(d.getHours()).padStart(2, "0");
    const mm = String(d.getMinutes()).padStart(2, "0");
    const ss = String(d.getSeconds()).padStart(2, "0");
    return `${y}-${m}-${day} ${hh}:${mm}:${ss}`;
  }
}

/** ---------- 兼容旧数据：补齐 createdAt/updatedAt/ts ---------- */
function normalizeData() {
  const now = Date.now();
  for (const id of Object.keys(chats)) {
    const chat = chats[id] || {};
    if (!chat.title) chat.title = "New Chat";
    if (!Array.isArray(chat.messages)) chat.messages = [];

    if (!chat.createdAt) {
      const first = chat.messages[0];
      chat.createdAt = first?.ts || now;
    }
    if (!chat.updatedAt) {
      const last = chat.messages[chat.messages.length - 1];
      chat.updatedAt = last?.ts || chat.createdAt;
    }

    for (const m of chat.messages) {
      if (!m.ts) m.ts = chat.createdAt;
    }

    chats[id] = chat;
  }
}
normalizeData();

/** ---------- 保存 ---------- */
function save() {
  localStorage.setItem("ds_chats", JSON.stringify(chats));
  localStorage.setItem("ds_current_chat", currentChatId || "");
  localStorage.setItem("ds_sidebar_hidden", sidebarHidden ? "1" : "0");
}

/** ---------- 侧栏显示/隐藏 ---------- */
function applySidebarState() {
  if (!appRootEl) return;
  appRootEl.classList.toggle("sidebar-hidden", sidebarHidden);
}
applySidebarState();

if (sidebarToggleBtn) {
  sidebarToggleBtn.onclick = () => {
    sidebarHidden = !sidebarHidden;
    applySidebarState();
    save();
  };
}

/** ---------- Chat 操作 ---------- */
function newChat() {
  const now = Date.now();
  currentChatId = crypto.randomUUID();
  chats[currentChatId] = {
    title: "New Chat",
    createdAt: now,
    updatedAt: now,
    messages: [],
  };
  save();
  renderChatList();
  renderMessages();
}

function deleteChat(id) {
  if (!id || !chats[id]) return;

  const title = chats[id].title || "This chat";
  const ok = confirm(`Delete "${title}" ?`);
  if (!ok) return;

  delete chats[id];

  // ✅ 关键：允许删除最后一个。删完后不自动 newChat()
  if (currentChatId === id) {
    const remainingIds = Object.keys(chats);
    currentChatId = remainingIds[0] || null;
  }

  save();
  renderChatList();
  renderMessages();
}

/** ---------- 渲染左侧列表（显示创建日期 + 删除按钮 + 按更新时间排序）---------- */
function renderChatList() {
  chatListEl.innerHTML = "";

  const entries = Object.entries(chats);
  entries.sort((a, b) => (b[1].updatedAt || 0) - (a[1].updatedAt || 0));

  // 如果没有任何 chat，列表保持空（不用提示，提示放在右侧 messages）
  if (entries.length === 0) return;

  for (const [id, chat] of entries) {
    const li = document.createElement("li");
    li.className = "chat-item";
    if (id === currentChatId) li.classList.add("active");

    const left = document.createElement("div");
    left.className = "chat-item-left";

    const title = document.createElement("div");
    title.className = "chat-title";
    title.textContent = chat.title || "New Chat";

    const date = document.createElement("div");
    date.className = "chat-date";
    date.textContent = formatChatDate(chat.createdAt || Date.now());

    left.appendChild(title);
    left.appendChild(date);

    const del = document.createElement("button");
    del.className = "chat-del";
    del.type = "button";
    del.title = "Delete";
    del.textContent = "🗑";
    del.onclick = (e) => {
      e.stopPropagation();
      deleteChat(id);
    };

    li.appendChild(left);
    li.appendChild(del);

    li.onclick = () => {
      currentChatId = id;
      save();
      renderChatList();
      renderMessages();
    };

    chatListEl.appendChild(li);
  }
}

/** ---------- 空状态 UI ---------- */
function renderEmptyState(kind) {
  // kind: "no-chat" | "no-messages"
  const div = document.createElement("div");
  div.className = "empty-state";

  if (kind === "no-chat") {
    div.innerHTML = `
      <h3>还没有会话</h3>
      <div>你可以：</div>
      <ul>
        <li>点击左上角 <code>＋</code> 创建新会话</li>
        <li>或者直接在下方输入内容并发送（会自动创建新会话）</li>
        <li>需要隐藏左侧列表：点顶部 <code>☰</code></li>
      </ul>
    `;
  } else {
    div.innerHTML = `
      <h3>这个会话还没有消息</h3>
      <div>在下方输入内容，按 <code>Enter</code> 发送；<code>Shift+Enter</code> 换行。</div>
    `;
  }

  messagesEl.appendChild(div);
}

/** ---------- 渲染消息（每条消息显示日期时间）---------- */
function renderMessages() {
  messagesEl.innerHTML = "";

  // 没有任何 chat
  if (!currentChatId || !chats[currentChatId]) {
    renderEmptyState("no-chat");
    return;
  }

  const chat = chats[currentChatId];
  const msgs = chat.messages || [];

  // 有 chat 但没消息
  if (msgs.length === 0) {
    renderEmptyState("no-messages");
    return;
  }

  for (const m of msgs) {
    const wrap = document.createElement("div");
    wrap.className = `message ${m.role} ${m.thinking ? "thinking" : ""}`;

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

    if (m.role === "assistant" && !m.thinking) {
      content.innerHTML = marked.parse(m.content || "");
      content.querySelectorAll("pre code").forEach((block) => {
        if (window.hljs) window.hljs.highlightElement(block);
      });
    } else {
      content.textContent = m.content || "";
    }

    const meta = document.createElement("div");
    meta.className = "msg-meta";
    meta.textContent = formatMsgDateTime(m.ts || Date.now());

    wrap.appendChild(content);
    wrap.appendChild(meta);

    messagesEl.appendChild(wrap);
  }

  messagesEl.scrollTop = messagesEl.scrollHeight;
}

/** ---------- 发送消息 ---------- */
sendBtn.onclick = async () => {
  const text = inputEl.value.trim();
  if (!text) return;

  sendBtn.disabled = true;
  sendBtn.textContent = "Sending...";

  // ✅ 如果你把最后一个 chat 删光了：这里会自动新建
  if (!currentChatId || !chats[currentChatId]) {
    newChat();
  }
  const chat = chats[currentChatId];

  const now = Date.now();

  // user 消息带时间戳
  chat.messages.push({ role: "user", content: text, ts: now });
  chat.updatedAt = now;
  inputEl.value = "";

  // thinking 消息也带时间戳（后续只改内容/ts）
  const thinkingMsg = { role: "assistant", content: "🤔 思考中…", thinking: true, ts: Date.now() };
  chat.messages.push(thinkingMsg);
  chat.updatedAt = thinkingMsg.ts;

  renderMessages();
  save();

  try {
    const res = await fetch("/api/chat", {
      method: "POST",
      headers: { "Content-Type": "application/json" },
      body: JSON.stringify({
        model: document.getElementById("modelSelect").value || "deepseek-chat",
        messages: chat.messages.filter((m) => !m.thinking),
        temperature: parseFloat(document.getElementById("tempInput").value || 0.7),
      }),
    });

    if (!res.ok) throw new Error(`HTTP ${res.status}`);

    const data = await res.json();

    thinkingMsg.thinking = false;
    thinkingMsg.content = data.reply || "No response";
    thinkingMsg.ts = Date.now(); // ✅ 用“收到回复的时间”
    chat.updatedAt = thinkingMsg.ts;

    if (chat.title === "New Chat") {
      chat.title = text.slice(0, 20);
    }
  } catch (e) {
    thinkingMsg.thinking = false;
    thinkingMsg.content = "❌ 请求失败";
    thinkingMsg.ts = Date.now();
    chat.updatedAt = thinkingMsg.ts;
    console.error(e);
  } finally {
    sendBtn.disabled = false;
    sendBtn.textContent = "Send";
  }

  save();
  renderChatList();
  renderMessages();
};

/** Enter=send, Shift+Enter=newline */
inputEl.addEventListener("keydown", (e) => {
  if (e.key === "Enter" && !e.shiftKey) {
    e.preventDefault();
    sendBtn.click();
  }
});

newChatBtn.onclick = newChat;

clearBtn.onclick = () => {
  if (!currentChatId || !chats[currentChatId]) return;
  const chat = chats[currentChatId];
  chat.messages = [];
  chat.title = "New Chat";
  chat.updatedAt = Date.now();
  save();
  renderChatList();
  renderMessages();
};

/** ---------- 初始化 ---------- */
renderChatList();
renderMessages();