/* 记事本：textarea + WebSocket 实时同步 + 心跳。
   - 文本以整文本 debounce 400ms 后发服务端，服务端存为新版本并广播给其他端。
   - 收到他人 update 时用 diff 应用变更，保留本地光标位置（按相对偏移调整）。
   - 收到 cleared 清空本地 textarea。
   - 心跳 3s 一次 ping；服务端 15s 无心跳判失活会主动断连，前端据此重连。 */
(function () {
  "use strict";
  const { toast, copyText } = window.ZK;

  // ---------- 从 URL 解析 board_id ----------
  const m = location.pathname.match(/^\/api\/wb-page\/([^/]+)\/?$/);
  let boardId = m ? decodeURIComponent(m[1]) : "default";
  if (!/^[a-zA-Z0-9_-]{1,64}$/.test(boardId)) boardId = "default";
  document.getElementById("boardId").textContent = boardId;

  // ---------- DOM ----------
  const editor = document.getElementById("editor");
  const clearBtn = document.getElementById("clearBtn");
  const copyBtn = document.getElementById("copyBtn");
  const copyLinkBtn = document.getElementById("copyLinkBtn");
  const statusEl = document.getElementById("status");
  const onlineEl = document.getElementById("online");

  // ---------- 状态 ----------
  let ws = null;
  // 每个 tab 独立的 client_id（用 sessionStorage 而非 localStorage，避免同浏览器
  // 多 tab 共享 id 导致收到的 update 被误判为「自己的」而跳过不同步）。
  // 服务端已用 exclude=conn 排除发送者，前端不再用 client_id 跳过 update。
  let clientId = sessionStorage.getItem("wb_cid") || "";
  if (!clientId) {
    clientId = "c_" + Math.random().toString(36).slice(2, 10);
    sessionStorage.setItem("wb_cid", clientId);
  }
  let heartbeatTimer = null;
  let reconnectTimer = null;
  let connected = false;
  let lastSentText = "";      // 上次发到服务端的文本（避免无变更时重复发）
  let suppressInput = false;  // 应用远端更新时抑制 input 事件，防回环
  let debounceTimer = null;

  // ---------- 本地编辑 -> debounce -> 发送 ----------
  editor.addEventListener("input", () => {
    if (suppressInput) return;
    scheduleSend();
  });

  function scheduleSend() {
    if (debounceTimer) clearTimeout(debounceTimer);
    debounceTimer = setTimeout(() => {
      debounceTimer = null;
      const text = editor.value;
      if (text === lastSentText) return;
      lastSentText = text;
      send({ type: "edit", content: text });
    }, 400);
  }

  function flushSend() {
    if (debounceTimer) {
      clearTimeout(debounceTimer);
      debounceTimer = null;
      const text = editor.value;
      if (text !== lastSentText) {
        lastSentText = text;
        send({ type: "edit", content: text });
      }
    }
  }

  clearBtn.addEventListener("click", () => {
    if (!connected) { flashStatus("未连接"); return; }
    if (!confirm("确定清空全部内容？所有人的内容都会被清除。")) return;
    send({ type: "clear" });
  });

  copyBtn.addEventListener("click", async () => {
    const text = editor.value;
    if (!text) { toast("内容为空"); return; }
    const ok = await copyText(text);
    toast(ok ? "已复制全部文本" : "复制失败");
  });

  copyLinkBtn.addEventListener("click", async () => {
    const url = `${location.origin}/api/wb-page/${boardId}`;
    const ok = await copyText(url);
    toast(ok ? "链接已复制" : "复制失败");
  });

  // ---------- 应用远端更新（保留光标） ----------
  // 策略：用最长公共前后缀算出变更区间，仅替换该区间，光标按相对位置调整。
  // 若本地有未发送的编辑（editor.value !== lastSentText），合并后重新 scheduleSend，
  // 避免本地编辑被远端覆盖后因 lastSentText 短路而丢弃。
  function applyRemoteUpdate(newText) {
    const oldText = editor.value;
    if (newText === oldText) return;

    const selStart = editor.selectionStart;
    const selEnd = editor.selectionEnd;

    // 算公共前缀
    let prefix = 0;
    const minLen = Math.min(oldText.length, newText.length);
    while (prefix < minLen && oldText[prefix] === newText[prefix]) prefix++;

    // 算公共后缀（不能与前缀重叠）
    let suffixOld = oldText.length;
    let suffixNew = newText.length;
    while (suffixOld > prefix && suffixNew > prefix && oldText[suffixOld - 1] === newText[suffixNew - 1]) {
      suffixOld--;
      suffixNew--;
    }

    const hadPending = editor.value !== lastSentText;
    suppressInput = true;
    // 用 setRangeText 替换 [prefix, suffixOld) 为 newText[prefix, suffixNew)
    editor.setRangeText(newText.slice(prefix, suffixNew), prefix, suffixOld, "end");
    suppressInput = false;
    lastSentText = editor.value;

    // 调整光标：若光标在变更区间之前，不动；在之后，平移差值；在区间内，移到区间末尾
    const delta = (suffixNew - prefix) - (suffixOld - prefix);
    let newStart = selStart, newEnd = selEnd;
    if (selStart <= prefix) {
      // 光标在变更前，不变
    } else if (selStart >= suffixOld) {
      // 光标在变更后，平移
      newStart = selStart + delta;
      newEnd = selEnd + delta;
    } else {
      // 光标在变更区间内，移到区间末尾
      newStart = newEnd = suffixNew;
    }
    try {
      editor.setSelectionRange(newStart, newEnd);
    } catch {}
    // 仅当编辑器当前有焦点时恢复焦点，避免抢其它控件焦点
    if (document.activeElement === editor) editor.focus();

    // 本地有未发送编辑被合并了，重新安排发送，避免被丢弃
    if (hadPending) scheduleSend();
  }

  // ---------- WebSocket ----------
  function wsUrl() {
    const proto = location.protocol === "https:" ? "wss:" : "ws:";
    return `${proto}//${location.host}/api/ws/wb/${encodeURIComponent(boardId)}`;
  }

  function connect() {
    setStatus("连接中…");
    try {
      ws = new WebSocket(wsUrl());
    } catch (e) {
      scheduleReconnect();
      return;
    }
    ws.onopen = () => {
      connected = true;
      setStatus("已连接", false);
      onlineEl.classList.remove("off");
      send({ type: "hello", client_id: clientId });
      startHeartbeat();
    };
    ws.onmessage = (ev) => onMessage(ev.data);
    ws.onclose = () => onLost("连接已关闭");
    ws.onerror = () => { /* close 会跟进 */ };
  }

  function onMessage(raw) {
    let msg;
    try { msg = JSON.parse(raw); } catch { return; }
    switch (msg.type) {
      case "init":
        // 连接建立时服务端下发当前文本。若本地有未发送编辑（断线期间输入的），
        // 不直接覆盖，而是把本地编辑作为最新版本发上去（last-writer-wins），
        // 避免断线期间的编辑被静默丢弃。
        if (editor.value && editor.value !== lastSentText) {
          lastSentText = editor.value;
          send({ type: "edit", content: editor.value });
        } else {
          suppressInput = true;
          editor.value = msg.content || "";
          lastSentText = editor.value;
          suppressInput = false;
          editor.focus();
        }
        setStatus("已同步", false);
        break;
      case "pong":
        break;
      case "update":
        // 服务端 broadcast 已用 exclude=conn 排除发送者，收到即他人编辑，直接应用。
        applyRemoteUpdate(msg.content || "");
        flashStatus("对方有更新");
        break;
      case "cleared":
        suppressInput = true;
        editor.value = "";
        lastSentText = "";
        suppressInput = false;
        flashStatus(msg.client_id === clientId ? "已清空" : "对方清空了内容");
        break;
      case "error":
        flashStatus(msg.msg || "错误", true);
        break;
    }
  }

  function send(obj) {
    if (ws && ws.readyState === WebSocket.OPEN) {
      try { ws.send(JSON.stringify(obj)); } catch {}
    }
  }

  function startHeartbeat() {
    stopHeartbeat();
    heartbeatTimer = setInterval(() => send({ type: "ping" }), 3000);
  }
  function stopHeartbeat() {
    if (heartbeatTimer) { clearInterval(heartbeatTimer); heartbeatTimer = null; }
  }

  function onLost(reason) {
    connected = false;
    stopHeartbeat();
    onlineEl.classList.add("off");
    setStatus(reason + "，重连中…", true);
    scheduleReconnect();
  }

  function scheduleReconnect() {
    if (reconnectTimer) return;
    reconnectTimer = setTimeout(() => {
      reconnectTimer = null;
      connect();
    }, 2000);
  }

  function setStatus(text, isErr) {
    statusEl.textContent = text;
    statusEl.classList.add("show");
    statusEl.classList.toggle("err", !!isErr);
  }
  let statusTimer = null;
  function flashStatus(text, isErr) {
    setStatus(text, isErr);
    clearTimeout(statusTimer);
    statusTimer = setTimeout(() => statusEl.classList.remove("show"), 1600);
  }

  // ---------- 启动 ----------
  // 先 GET /api/wb/{id} 确保白板存在（不存在则服务端新建），再连 WS
  fetch(`/api/wb/${encodeURIComponent(boardId)}`, { headers: { accept: "application/json" } })
    .then((r) => (r.ok ? r.json() : null))
    .then((body) => {
      if (body && typeof body.content === "string") {
        editor.value = body.content;
        lastSentText = body.content;
      }
      connect();
    })
    .catch(() => { connect(); });

  // 页面可见性：重新可见时若已断连则主动重连；隐藏时 flush 未发送的编辑
  document.addEventListener("visibilitychange", () => {
    if (document.visibilityState === "visible") {
      if (!ws || ws.readyState !== WebSocket.OPEN) {
        if (reconnectTimer) { clearTimeout(reconnectTimer); reconnectTimer = null; }
        connect();
      }
    } else {
      flushSend();
    }
  });

  // 离开前 flush 未发送编辑
  window.addEventListener("beforeunload", () => {
    flushSend();
    stopHeartbeat();
    if (reconnectTimer) clearTimeout(reconnectTimer);
    try { ws && ws.close(); } catch {}
  });
})();