/**
 * 心经 / 金刚经 诵读页前端逻辑：经文渲染、分页阅读、逐段高亮朗读、音色选择。
 */

// ===== 经文数据 =====
// segments 项：{ h: 品名(可选), g: 品名小注(可选), t: 正文 }
// ===== 经文数据（外置） =====
// 每部经对应 sutras/<id>.json：{id, name, title, seal, cat, translator, source, sourceUrl, pageSize, segments[{h?,g?,t}]}
// 启动时经 /api/sutras 拉目录清单建下拉，选中时按需加载经文并缓存。
// 新增经典 = 往 sutras/ 目录放一个 JSON 文件（order 字段决定排序），无需改动任何代码。
const SUTRAS = []; // 目录清单 [{id,name,cat,order}]，启动时填充
const sutraDataCache = new Map(); // id → 完整经文数据（加载一次后复用）
let selectToken = 0; // 切换令牌，防止快速连续切换时旧响应覆盖新选择

// ===== 可选音色（模型 qwen3-tts-flash） =====
const VOICE_GROUPS = [
  {
    label: "诵读音色",
    voices: [
      ["Seren", "Seren 塞伦 · 女声"],
      ["Ethan", "Ethan 伊森 · 男声"],
    ],
  },
];

const sutraEl = document.getElementById("sutra");
const sutraSelect = document.getElementById("sutra-select");
const voiceSelect = document.getElementById("voice-select");
const btnPlay = document.getElementById("btn-play");
const statusEl = document.getElementById("status");
const progressEl = document.getElementById("progress");
const audioEl = document.getElementById("audio");
const btnLayout = document.getElementById("btn-layout");
const pagerEl = document.getElementById("pager");
const playerCard = document.getElementById("player-card");
const btnExpand = document.getElementById("btn-expand");
const btnPrev = document.getElementById("btn-prev");
const btnNext = document.getElementById("btn-next");
const btnLoop = document.getElementById("btn-loop");
const btnBgm = document.getElementById("btn-bgm");
const timerSelect = document.getElementById("timer-select");
const rateSelect = document.getElementById("rate-select");
const btnNight = document.getElementById("btn-night");
const sleepRemainEl = document.getElementById("sleep-remaining");
const btnJumpNow = document.getElementById("btn-jump-now");
const pageInfo = document.getElementById("page-info");

/** 音频缓存：key = `${经id}|${音色}|${段序号}`，value = Blob */
const audioCache = new Map();
let playToken = 0; // 播放会话令牌，防止旧异步任务串扰
let playing = false;
let inflight = null; // 进行中的 fetch AbortController
let loopMode = false; // 循环诵读开关：播完全文回到开头继续
let bgmOn = false; // 背景音乐开关
let sleepEndAt = 0; // 定时停止的截止时间戳（毫秒），0 = 未开启
let sleepTimer = null; // 定时器句柄（前台兜底；后台由 onTimeUpdate 判定截止时间）
let loopAutoByTimer = false; // 循环是否为设定定时时自动打开的（是则定时结束一并关回）

// ===== 用户偏好记忆（localStorage）：经、音色、字号、循环、配乐、语速、夜间 =====
const PREFS_KEY = "fj.prefs.v1";
const prefs = (() => {
  try {
    return JSON.parse(localStorage.getItem(PREFS_KEY)) || {};
  } catch {
    return {};
  }
})();
/** 写一条偏好并落盘；localStorage 不可用时静默降级为仅内存。 */
function savePref(key, value) {
  prefs[key] = value;
  try {
    localStorage.setItem(PREFS_KEY, JSON.stringify(prefs));
  } catch { /* 隐私模式等场景忽略 */ }
}
let segTimes = []; // 合并音频中各段的起始秒
let currentSeg = -1; // 正在朗读的段号
let lastUserScroll = 0; // 用户最近一次手动滚动经文的时间戳（用于暂缓跟读强拽）
let cursorRaf = null; // 逐字光标 rAF 句柄

// ===== 背景音乐：Web Audio 实时合成颂钵泛音 drone（零资源文件、无缝循环） =====
let bgmCtx = null;
let bgmGain = null;
let bgmNodes = [];
let bgmBellTimer = null;
let bgmDrumTimer = null;
let bgmChimeTimer = null;
let bgmGlideTimer = null;
let bgmOscs = []; // {osc, ratio}，供基频滑变统一改频率
const BGM_ROOTS = [55, 65.41, 73.42, 82.41, 98]; // A1 C2 D2 E2 G2，低音区垫底
let bgmRoot = 73.42;

/** 基频慢移：只滑向相邻根音、16 秒缓慢过渡，变化若有似无，避免警报式的滑音。 */
function bgmGlide() {
  const idx = BGM_ROOTS.indexOf(bgmRoot);
  const neighbors = [idx - 1, idx + 1].filter((i) => i >= 0 && i < BGM_ROOTS.length);
  bgmRoot = BGM_ROOTS[neighbors[Math.floor(Math.random() * neighbors.length)]];
  const t = bgmCtx.currentTime;
  for (const { osc, ratio } of bgmOscs) {
    osc.frequency.cancelScheduledValues(t);
    osc.frequency.setValueAtTime(osc.frequency.value, t);
    osc.frequency.exponentialRampToValueAtTime(bgmRoot * ratio, t + 16);
  }
  bgmGlideTimer = setTimeout(() => { if (bgmGain) bgmGlide(); }, 50000 + Math.random() * 40000);
}

/** 给打击声部接随机方位的输出链，返回挂到主增益下的 GainNode。 */
function bgmStrikeOut(panRange) {
  const out = bgmCtx.createGain();
  if (bgmCtx.createStereoPanner) {
    const pan = bgmCtx.createStereoPanner();
    pan.pan.value = (Math.random() - 0.5) * 2 * panRange;
    out.connect(pan);
    pan.connect(bgmGain);
  } else {
    out.connect(bgmGain);
  }
  return out;
}

/** 晨钟一声：大钟的非谐泛音簇，毫秒级起音，泛音越高衰减越快（长达十余秒）。 */
function bgmBell() {
  const now = bgmCtx.currentTime;
  const root = [98, 110, 123.47][Math.floor(Math.random() * 3)]; // G2 / A2 / B2 附近的大钟
  const bellGain = bgmStrikeOut(0.8);
  bellGain.gain.setValueAtTime(0, now);
  bellGain.gain.linearRampToValueAtTime(0.5, now + 0.02);
  // 大钟泛音列：哼音 0.5、基音 1、小三度 1.19、五度 1.5、名义音 2、上泛音 2.74
  // [频率比, 振幅, 衰减秒数] —— 低频泛音余韵更长
  [[0.5, 0.5, 15], [1, 1, 13], [1.19, 0.3, 9], [1.5, 0.24, 7], [2.0, 0.18, 5], [2.74, 0.1, 3.5]].forEach(([ratio, amp, dur]) => {
    const o = bgmCtx.createOscillator();
    o.type = "sine";
    o.frequency.value = root * ratio;
    o.detune.value = (Math.random() - 0.5) * 5;
    const og = bgmCtx.createGain();
    og.gain.setValueAtTime(amp, now);
    og.gain.exponentialRampToValueAtTime(0.0001, now + dur);
    o.connect(og);
    og.connect(bellGain);
    o.start(now);
    o.stop(now + dur + 0.5);
    bgmNodes.push(o);
  });
}

/** 磬声一声：高音引磬，快起音 + 约 6 秒衰减的小泛音簇，稀疏点缀。 */
function bgmChime() {
  const now = bgmCtx.currentTime;
  const freq = [392, 523.25, 659.25, 783.99][Math.floor(Math.random() * 4)]; // 五声音阶附近
  const chimeGain = bgmStrikeOut(0.6);
  chimeGain.gain.setValueAtTime(0, now);
  chimeGain.gain.linearRampToValueAtTime(0.35, now + 0.03);
  chimeGain.gain.exponentialRampToValueAtTime(0.0001, now + 6);
  [[1, 1], [2.76, 0.28], [5.4, 0.08]].forEach(([ratio, amp]) => {
    const o = bgmCtx.createOscillator();
    o.type = "sine";
    o.frequency.value = freq * ratio;
    o.detune.value = (Math.random() - 0.5) * 6;
    const og = bgmCtx.createGain();
    og.gain.value = amp;
    o.connect(og);
    og.connect(chimeGain);
    o.start(now);
    o.stop(now + 6.5);
    bgmNodes.push(o);
  });
}

/** 暮鼓一记：低频膜鸣（72→44Hz 下滑）+ 短促噪声击边，钝而沉。 */
function bgmDrum() {
  const now = bgmCtx.currentTime;
  const drumGain = bgmStrikeOut(0.5);
  drumGain.gain.setValueAtTime(0, now);
  drumGain.gain.linearRampToValueAtTime(0.55, now + 0.012);
  drumGain.gain.exponentialRampToValueAtTime(0.0001, now + 1.8);

  // 鼓皮基音：起振约 72Hz，迅速下滑到 44Hz
  const o = bgmCtx.createOscillator();
  o.type = "sine";
  o.frequency.setValueAtTime(72, now);
  o.frequency.exponentialRampToValueAtTime(44, now + 0.3);
  o.connect(drumGain);
  o.start(now);
  o.stop(now + 2);
  bgmNodes.push(o);

  // 击边噪声：0.08s 噪声过 260Hz 带通，模拟鼓槌触皮的一声"扑"
  const len = Math.floor(bgmCtx.sampleRate * 0.08);
  const buf = bgmCtx.createBuffer(1, len, bgmCtx.sampleRate);
  const data = buf.getChannelData(0);
  for (let i = 0; i < len; i += 1) data[i] = Math.random() * 2 - 1;
  const noise = bgmCtx.createBufferSource();
  noise.buffer = buf;
  const bp = bgmCtx.createBiquadFilter();
  bp.type = "bandpass";
  bp.frequency.value = 260;
  bp.Q.value = 0.8;
  const ng = bgmCtx.createGain();
  ng.gain.setValueAtTime(0.4, now);
  ng.gain.exponentialRampToValueAtTime(0.0001, now + 0.15);
  noise.connect(bp);
  bp.connect(ng);
  ng.connect(drumGain);
  noise.start(now);
  bgmNodes.push(noise);
}

/**
 * 开始播放背景音乐：低频颂钵式泛音 drone 垫底（基频缓慢游走），
 * 叠稀疏的晨钟（大钟非谐泛音簇、长余韵）、暮鼓（低频膜鸣 + 击边噪声）
 * 与引磬（高音泛音点缀），三种寺院打击声部随机方位错开出现，
 * 方位随机、音量压在人声之下；2.5 秒淡入。需在用户手势内调用。
 */
function startBgm() {
  if (!bgmCtx) bgmCtx = new (window.AudioContext || window.webkitAudioContext)();
  if (bgmCtx.state === "suspended") bgmCtx.resume();
  const now = bgmCtx.currentTime;
  const g = bgmCtx.createGain();
  g.gain.setValueAtTime(0, now);
  // 低通只做轻微软化，保留高频空气感（太低会发闷）
  const lp = bgmCtx.createBiquadFilter();
  lp.type = "lowpass";
  lp.frequency.value = 3200;
  lp.Q.value = 0.4;
  g.connect(lp);
  lp.connect(bgmCtx.destination);

  const base = bgmRoot; // 初始根音，之后由 bgmGlide 慢移
  const partials = [[1, 0.45], [2.02, 0.2], [3.01, 0.13], [4.16, 0.08], [5.43, 0.05], [7.2, 0.025]];
  const nodes = [];
  bgmOscs = [];
  partials.forEach(([ratio, amp], pi) => {
    const og = bgmCtx.createGain();
    og.gain.value = amp;
    // 泛音左右宽展开 + 极慢声像漂移，空间缓慢呼吸
    if (bgmCtx.createStereoPanner) {
      const pan = bgmCtx.createStereoPanner();
      const side = pi % 2 === 0 ? -1 : 1;
      pan.pan.value = side * 0.6;
      og.connect(pan);
      pan.connect(g);
      const plfo = bgmCtx.createOscillator();
      plfo.frequency.value = 0.02 + Math.random() * 0.03;
      const plg = bgmCtx.createGain();
      plg.gain.value = 0.3;
      plfo.connect(plg);
      plg.connect(pan.pan);
      plfo.start(now + pi * 0.5);
      nodes.push(plfo);
    } else {
      og.connect(g);
    }
    // 双振荡器 ±3 音分失谐，产生颂钵的拍频颤动
    for (const det of [-3, 3]) {
      const osc = bgmCtx.createOscillator();
      osc.type = "sine";
      osc.frequency.value = base * ratio;
      osc.detune.value = det + (Math.random() - 0.5) * 2;
      osc.connect(og);
      osc.start(now + Math.random() * 0.3);
      nodes.push(osc);
      bgmOscs.push({ osc, ratio });
    }
    // 每个泛音带独立慢速呼吸，避免死板
    const lfo = bgmCtx.createOscillator();
    lfo.frequency.value = 0.04 + Math.random() * 0.07;
    const lg = bgmCtx.createGain();
    lg.gain.value = amp * 0.4;
    lfo.connect(lg);
    lg.connect(og.gain);
    lfo.start(now);
    nodes.push(lfo);
  });
  g.gain.linearRampToValueAtTime(0.07, now + 2.5); // 淡入，drone 压低垫底
  bgmGain = g;
  bgmNodes = nodes;

  // 晨钟：淡入后 4 秒先撞一声，之后每 30~55 秒一声
  const scheduleBell = () => {
    bgmBellTimer = setTimeout(() => {
      if (!bgmGain) return;
      bgmBell();
      scheduleBell();
    }, 30000 + Math.random() * 25000);
  };
  bgmBellTimer = setTimeout(() => {
    if (!bgmGain) return;
    bgmBell();
    scheduleBell();
  }, 4000);

  // 暮鼓：每 45~80 秒一记，偶尔连击两记（间隔约 2.4s）
  const scheduleDrum = () => {
    bgmDrumTimer = setTimeout(() => {
      if (!bgmGain) return;
      bgmDrum();
      if (Math.random() < 0.45) setTimeout(() => { if (bgmGain) bgmDrum(); }, 2400);
      scheduleDrum();
    }, 45000 + Math.random() * 35000);
  };
  scheduleDrum();

  // 引磬：最稀疏，每 60~100 秒一声清越点缀
  const scheduleChime = () => {
    bgmChimeTimer = setTimeout(() => {
      if (!bgmGain) return;
      bgmChime();
      scheduleChime();
    }, 60000 + Math.random() * 40000);
  };
  scheduleChime();

  // 首次基频滑变：约 50 秒后
  bgmGlideTimer = setTimeout(() => { if (bgmGain) bgmGlide(); }, 50000);
}

/** 停止背景音乐：1.5 秒淡出后停掉振荡器、钟鼓调度器并断开节点。 */
function stopBgm() {
  if (bgmBellTimer) {
    clearTimeout(bgmBellTimer);
    bgmBellTimer = null;
  }
  if (bgmDrumTimer) {
    clearTimeout(bgmDrumTimer);
    bgmDrumTimer = null;
  }
  if (bgmChimeTimer) {
    clearTimeout(bgmChimeTimer);
    bgmChimeTimer = null;
  }
  if (bgmGlideTimer) {
    clearTimeout(bgmGlideTimer);
    bgmGlideTimer = null;
  }
  if (!bgmCtx || !bgmGain) return;
  const g = bgmGain;
  const nodes = bgmNodes;
  const now = bgmCtx.currentTime;
  g.gain.cancelScheduledValues(now);
  g.gain.setValueAtTime(g.gain.value, now);
  g.gain.linearRampToValueAtTime(0, now + 1.5);
  bgmGain = null;
  bgmNodes = [];
  setTimeout(() => {
    nodes.forEach((n) => { try { n.stop(); } catch { /* 已停止 */ } });
    g.disconnect();
  }, 1700);
}

let sutra = null; // 当前经
let segments = []; // 当前经分段
let currentPage = 0;
let pageCount = 1;
let segEls = [];
let dots = [];

const currentVoice = () => voiceSelect.value;
const pageOf = (i) => Math.floor(i / sutra.pageSize);

// ===== 音色下拉 =====
VOICE_GROUPS.forEach((group) => {
  const target = VOICE_GROUPS.length > 1 ? voiceSelect.appendChild(Object.assign(document.createElement("optgroup"), { label: group.label })) : voiceSelect;
  group.voices.forEach(([value, label]) => {
    const opt = document.createElement("option");
    opt.value = value;
    opt.textContent = label;
    target.appendChild(opt);
  });
});
voiceSelect.value = "Seren";

// ===== 经典下拉：按 cat 分组（佛经 / 道家），清单来自 /api/sutras =====
function buildSutraOptions() {
  sutraSelect.innerHTML = "";
  const cats = [...new Set(SUTRAS.map((s) => s.cat || "其他"))];
  cats.forEach((cat) => {
    const group = sutraSelect.appendChild(Object.assign(document.createElement("optgroup"), { label: cat }));
    SUTRAS.filter((s) => (s.cat || "其他") === cat).forEach((s) => {
      const opt = document.createElement("option");
      opt.value = s.id;
      opt.textContent = s.name;
      group.appendChild(opt);
    });
  });
}

// ===== 状态 / 高亮 =====
let statusBase = ""; // 状态主干文字；定时开启时自动追加剩余倒计时
function setStatus(text, isError = false) {
  statusBase = text;
  statusEl.classList.toggle("error", isError);
  renderStatus();
}

/** 渲染状态条：主干 + 定时剩余 mm:ss；移动端同步到播放旁的剩余胶囊。 */
function renderStatus() {
  let remain = "";
  if (sleepEndAt) {
    const s = Math.max(0, Math.ceil((sleepEndAt - Date.now()) / 1000));
    remain = `${Math.floor(s / 60)}:${String(s % 60).padStart(2, "0")}`;
  }
  statusEl.textContent = statusBase + (remain ? ` · ${remain} 后停` : "");
  sleepRemainEl.textContent = remain ? `⏱ ${remain}` : "";
  sleepRemainEl.classList.toggle("show", !!sleepEndAt);
}
setInterval(renderStatus, 1000);

function setPlayingUI(on) {
  playing = on;
  btnPlay.classList.toggle("playing", on);
  btnPlay.setAttribute("aria-label", on ? "停止" : "播放");
  btnPlay.querySelector(".play-label").textContent = on ? "停 止" : "播 放";
  if ("mediaSession" in navigator) navigator.mediaSession.playbackState = on ? "playing" : "none";
}

/** 更新锁屏/控制中心元数据：经名 + 音色 + 印章封面，并接管播放控制按键。 */
function updateMediaSession() {
  if (!("mediaSession" in navigator) || !sutra) return;
  navigator.mediaSession.metadata = new MediaMetadata({
    title: `《${sutra.name}》诵读`,
    artist: currentVoice(),
    album: sutra.title,
    artwork: [
      { src: "icon-180.png", sizes: "180x180", type: "image/png" },
      { src: "icon.svg", sizes: "any", type: "image/svg+xml" },
    ],
  });
}

function highlight(index) {
  segEls.forEach((el) => {
    const i = Number(el.dataset.index);
    el.classList.toggle("playing", i === index);
    el.classList.toggle("done", i < index);
  });
  dots.forEach((d, i) => {
    d.classList.toggle("now", i === index);
    d.classList.toggle("done", index >= 0 && i < index);
  });
  // 跟读滚动：定位到光标所在行（而非整段中心）；
  // 用户刚手动滚动过（6 秒内）则不打断阅读，改由"回到诵读处"按钮兜底
  const active = segEls.find((el) => Number(el.dataset.index) === index);
  const userBusy = playing && Date.now() - lastUserScroll < 6000;
  if (active && !userBusy) {
    const target = active.querySelector(".ch.cur") || active;
    target.scrollIntoView({ behavior: reduceMotionMQ.matches ? "auto" : "smooth", block: "center", inline: "center" });
  }
  requestAnimationFrame(updateJumpNow);
}

/** 诵读光标是否在经文视区内；不在则显示"回到诵读处"浮动按钮。 */
function updateJumpNow() {
  if (!playing || currentSeg < 0) {
    btnJumpNow.hidden = true;
    return;
  }
  const active = segEls.find((el) => Number(el.dataset.index) === currentSeg);
  if (!active) {
    btnJumpNow.hidden = false; // 当前段不在本页，提示可跳回
    return;
  }
  const target = active.querySelector(".ch.cur") || active;
  const r = target.getBoundingClientRect();
  const c = sutraEl.getBoundingClientRect();
  btnJumpNow.hidden = r.top >= c.top && r.bottom <= c.bottom;
}

function clearHighlight() {
  segEls.forEach((el) => {
    el.classList.remove("playing", "done");
    el.querySelectorAll(".ch").forEach((s) => s.classList.remove("read", "cur"));
    delete el.dataset.cursorN;
  });
  dots.forEach((d) => d.classList.remove("now", "done"));
  if (cursorRaf) {
    cancelAnimationFrame(cursorRaf);
    cursorRaf = null;
  }
}

const reduceMotionMQ = matchMedia("(prefers-reduced-motion: reduce)");

// ===== 渲染 =====
function renderDots() {
  progressEl.innerHTML = "";
  dots = segments.map((_, i) => {
    const d = document.createElement("span");
    d.className = "dot";
    d.title = `第 ${i + 1} 段，点击起读`;
    d.addEventListener("click", () => playFrom(i));
    progressEl.appendChild(d);
    return d;
  });
}

/** 渲染当前页的经文分段（含品名标题）。 */
function renderPage(page) {
  currentPage = page;
  sutraEl.innerHTML = "";
  const start = page * sutra.pageSize;
  const end = Math.min(start + sutra.pageSize, segments.length);
  segEls = [];

  for (let i = start; i < end; i += 1) {
    const seg = segments[i];
    if (seg.h) {
      const h = document.createElement("h4");
      h.className = "chap";
      h.innerHTML = "";
      const name = document.createElement("span");
      name.className = "chap-name";
      name.textContent = seg.h;
      h.appendChild(name);
      if (seg.g) {
        const gloss = document.createElement("span");
        gloss.className = "chap-gloss";
        gloss.textContent = seg.g;
        h.appendChild(gloss);
      }
      sutraEl.appendChild(h);
    }
    const p = document.createElement("p");
    p.className = "seg";
    p.dataset.index = i;
    p.textContent = seg.t;
    p.setAttribute("role", "button");
    p.setAttribute("tabindex", "0");
    const label = seg.h ? seg.h : `第 ${i + 1} 段`;
    p.setAttribute("aria-label", `朗读：${label}`);
    p.addEventListener("click", () => playFrom(i));
    p.addEventListener("keydown", (e) => {
      if (e.key === "Enter" || e.key === " ") {
        e.preventDefault();
        playFrom(i);
      }
    });
    sutraEl.appendChild(p);
    segEls.push(p);
  }

  sutraEl.scrollTop = 0;
  sutraEl.scrollLeft = 0;
  updatePager();
}

function updatePager() {
  const multi = pageCount > 1;
  pagerEl.hidden = !multi;
  pageInfo.textContent = `第 ${currentPage + 1} / ${pageCount} 页`;
  btnPrev.disabled = currentPage === 0;
  btnNext.disabled = currentPage === pageCount - 1;
}

/** 手动翻页（停止当前朗读）。 */
function gotoPage(page) {
  if (page < 0 || page >= pageCount || page === currentPage) return;
  stopPlayback();
  renderPage(page);
  setStatus(`已翻到第 ${page + 1} / ${pageCount} 页`);
}

/** 切换经文：按需加载 sutras/<id>.json 并缓存；selectToken 防止快速切换时旧响应覆盖。 */
async function selectSutra(id) {
  const meta = SUTRAS.find((s) => s.id === id);
  if (!meta || (sutra && sutra.id === id)) return;
  const token = ++selectToken;
  if (!sutraDataCache.has(id)) {
    setStatus(`正在载入《${meta.name}》…`);
    try {
      const resp = await fetch(`sutras/${id}.json`);
      if (!resp.ok) throw new Error(`HTTP ${resp.status}`);
      sutraDataCache.set(id, await resp.json());
    } catch (err) {
      if (token === selectToken) setStatus(`《${meta.name}》载入失败：${err.message}`, true);
      return;
    }
  }
  if (token !== selectToken) return;
  stopPlayback();
  sutra = sutraDataCache.get(id);
  savePref("sutra", id);
  segments = sutra.segments;
  pageCount = Math.ceil(segments.length / sutra.pageSize);

  document.title = sutra.name;
  document.getElementById("sutra-title").textContent = sutra.title;
  document.getElementById("sutra-sub").textContent = sutra.translator;
  const sealEl = document.getElementById("seal");
  sealEl.textContent = sutra.seal;
  sealEl.dataset.chars = sutra.seal.length;
  const src = document.getElementById("sutra-source");
  src.textContent = sutra.source;
  src.href = sutra.sourceUrl;

  sutraSelect.value = id;
  sheetSyncFns.get(sutraSelect)?.();

  renderDots();
  renderPage(0);
  setStatus(`已切换到《${sutra.name}》· 共 ${segments.length} 段${pageCount > 1 ? ` / ${pageCount} 页` : ""}`);
}

// ===== 播放控制 =====
/** 取消进行中的请求与播放，令牌递增使旧循环失效。 */
function stopPlayback() {
  playToken += 1;
  setPlayingUI(false);
  btnPlay.classList.remove("preparing");
  if (inflight) {
    inflight.abort();
    inflight = null;
  }
  audioEl.pause();
  audioEl.ontimeupdate = null;
  audioEl.onended = null;
  stopBgm();
  clearHighlight();
  btnJumpNow.hidden = true;
  currentSeg = -1;
}

/**
 * 获取指定段的音频 Blob，命中缓存则直接返回。
 * 失败自动重试（最多 3 次，间隔 1s/2s 递增），吸收服务重启等瞬时 502；
 * 用户停止播放导致的 AbortError 不重试。
 * @param {number} index 段序号
 * @returns {Promise<Blob>} 音频数据
 */
async function fetchSegment(index) {
  const key = `${sutra.id}|${currentVoice()}|${index}`;
  if (audioCache.has(key)) return audioCache.get(key);

  let lastErr = null;
  for (let attempt = 0; attempt < 3; attempt += 1) {
    if (attempt > 0) await new Promise((r) => setTimeout(r, attempt * 1000));
    inflight = new AbortController();
    try {
      const resp = await fetch("/api/tts", {
        method: "POST",
        headers: { "Content-Type": "application/json" },
        body: JSON.stringify({ text: segments[index].t, voice: currentVoice() }),
        signal: inflight.signal,
      });
      if (!resp.ok) {
        const err = await resp.json().catch(() => ({}));
        throw new Error(err.error || `HTTP ${resp.status}`);
      }
      const blob = await resp.blob();
      audioCache.set(key, blob);
      return blob;
    } catch (err) {
      if (err.name === "AbortError") throw err; // 主动停止，不重试
      lastErr = err;
    } finally {
      inflight = null;
    }
  }
  throw lastErr;
}

/**
 * 解析 WAV 文件头，返回 {rate, channels, pcm}；格式不符返回 null。
 * @param {ArrayBuffer} buf WAV 数据
 */
function parseWav(buf) {
  const v = new DataView(buf);
  const tag = (o) => v.getUint32(o, true); // 块 ID 按小端读
  if (buf.byteLength < 44 || tag(0) !== 0x46464952) return null; // 'RIFF'
  let off = 12;
  let fmt = null;
  let pcm = null;
  while (off + 8 <= buf.byteLength) {
    const id = tag(off);
    const sz = v.getUint32(off + 4, true);
    if (id === 0x20746d66) { // 'fmt '
      fmt = { channels: v.getUint16(off + 10, true), rate: v.getUint32(off + 12, true), bits: v.getUint16(off + 22, true) };
    } else if (id === 0x61746164) { // 'data'
      // 流式编码的 WAV 可能写占位符长度（如 0x7fffffxx），按实际文件长度截断
      const realLen = Math.min(sz, buf.byteLength - (off + 8));
      pcm = new Uint8Array(buf, off + 8, realLen);
      break;
    }
    off += 8 + sz + (sz % 2);
  }
  if (!fmt || !pcm || fmt.bits !== 16) return null;
  return { rate: fmt.rate, channels: fmt.channels, pcm };
}

/**
 * 将全部段落 PCM 合并为一个 WAV：段间 0.8s 静音、末尾 3s 静音（循环间隔）。
 * 合并成单文件后整个诵读只播一个音频，无 JS 事件链，手机锁屏/后台也不中断。
 * @param {Blob[]} blobs 各段音频
 * @returns {Promise<{url: string, times: number[]}>} 音频地址与各段起始秒
 */
async function buildCombined(blobs) {
  const parts = [];
  const times = [];
  let rate = 24000;
  let channels = 1;
  let cursor = 0; // 已写入字节数
  for (const b of blobs) {
    const w = parseWav(await b.arrayBuffer());
    if (!w) throw new Error("音频格式不支持");
    rate = w.rate;
    channels = w.channels;
    if (parts.length) {
      const gap = new Uint8Array(Math.floor(rate * 0.8) * channels * 2);
      parts.push(gap);
      cursor += gap.length;
    }
    times.push(cursor / (rate * channels * 2));
    parts.push(w.pcm);
    cursor += w.pcm.length;
  }
  parts.push(new Uint8Array(Math.floor(rate * 3) * channels * 2)); // 尾部 3s 静音
  const total = parts.reduce((s, p) => s + p.length, 0);
  const out = new ArrayBuffer(44 + total);
  const v = new DataView(out);
  const wstr = (o, s) => { for (let k = 0; k < s.length; k += 1) v.setUint8(o + k, s.charCodeAt(k)); };
  wstr(0, "RIFF"); v.setUint32(4, 36 + total, true); wstr(8, "WAVE");
  wstr(12, "fmt "); v.setUint32(16, 16, true); v.setUint16(20, 1, true);
  v.setUint16(22, channels, true); v.setUint32(24, rate, true);
  v.setUint32(28, rate * channels * 2, true); v.setUint16(32, channels * 2, true); v.setUint16(34, 16, true);
  wstr(36, "data"); v.setUint32(40, total, true);
  let o = 44;
  for (const p of parts) {
    new Uint8Array(out, o, p.length).set(p);
    o += p.length;
  }
  return { url: URL.createObjectURL(new Blob([out], { type: "audio/wav" })), times };
}

/** 把段落文字逐字包成 .ch span（仅当前诵读段需要，幂等）。 */
function wrapChars(el) {
  if (el.dataset.wrapped) return;
  const frag = document.createDocumentFragment();
  for (const c of el.textContent) {
    const s = document.createElement("span");
    s.className = "ch";
    s.textContent = c;
    frag.appendChild(s);
  }
  el.innerHTML = "";
  el.appendChild(frag);
  el.dataset.wrapped = "1";
}

/**
 * 逐字光标：按音频当前时间在当前段内按比例推进，
 * 已读字染朱砂、当前字挂金色下划线光标。TTS 无逐字时间戳，按语速均匀估算。
 */
function cursorTick() {
  if (!playing || !segTimes.length) {
    cursorRaf = null;
    return;
  }
  const t = audioEl.currentTime;
  let i = segTimes.length - 1;
  while (i > 0 && segTimes[i] > t) i -= 1;
  const active = segEls.find((el) => Number(el.dataset.index) === i);
  if (active) {
    wrapChars(active);
    const chs = active.querySelectorAll(".ch");
    const segDur = (i + 1 < segTimes.length ? segTimes[i + 1] - 0.8 : audioEl.duration - 3) - segTimes[i];
    const n = Math.min(chs.length, Math.floor(((t - segTimes[i]) / Math.max(segDur, 0.1)) * chs.length));
    const prev = Number(active.dataset.cursorN ?? -1);
    if (n !== prev) {
      const lo = Math.max(0, Math.min(n, prev));
      const hi = Math.max(n, prev);
      for (let k = lo; k <= hi && k < chs.length; k += 1) chs[k].classList.toggle("read", k < n);
      active.dataset.cursorN = n;
      const old = active.querySelector(".ch.cur");
      old?.classList.remove("cur");
      if (n < chs.length) chs[n].classList.add("cur");
    }
    cursorTick._n = (cursorTick._n || 0) + 1;
    if (cursorTick._n % 15 === 0) {
      // 光标行跟随：光标走出视区 25%~75% 舒适带时，平滑滚回中部
      if (Date.now() - lastUserScroll >= 6000 && chs[n]) {
        const r = chs[n].getBoundingClientRect();
        const c = sutraEl.getBoundingClientRect();
        if (r.top < c.top + c.height * 0.25 || r.bottom > c.top + c.height * 0.75) {
          chs[n].scrollIntoView({ behavior: reduceMotionMQ.matches ? "auto" : "smooth", block: "center", inline: "center" });
        }
      }
      updateJumpNow();
    }
  }
  cursorRaf = requestAnimationFrame(cursorTick);
}

/** 播放进度回调：按当前时间定位段号，高亮并自动翻页滚动；顺带判定定时停止。 */
function onTimeUpdate() {
  if (sleepEndAt && Date.now() >= sleepEndAt) {
    fireSleepTimer();
    return;
  }
  const t = audioEl.currentTime;
  let i = segTimes.length - 1;
  while (i > 0 && segTimes[i] > t) i -= 1;
  if (i === currentSeg) return;
  currentSeg = i;
  const targetPage = pageOf(i);
  if (targetPage !== currentPage) renderPage(targetPage);
  highlight(i);
}

/**
 * 从第 index 段开始连续朗读到全文结束；开启循环时 audio.loop 原生回卷。
 * 先并发补齐所有段音频再合并为单个 WAV 播放，中途无 JS 事件链衔接，
 * 手机锁屏/后台不会中断；高亮靠 timeupdate 按 segTimes 时间轴定位。
 */
async function playFrom(index) {
  stopPlayback();
  const token = ++playToken;
  setPlayingUI(true);
  // 准备阶段按钮脉冲 + 文字提示（移动端没有状态栏，这条反馈很关键）
  btnPlay.classList.add("preparing");
  btnPlay.querySelector(".play-label").textContent = "准备中";
  setStatus("正在准备音频…");

  const blobs = new Array(segments.length);
  let next = 0;
  let done = 0;
  const worker = async () => {
    while (next < segments.length && token === playToken) {
      const i = next;
      next += 1;
      blobs[i] = await fetchSegment(i);
      done += 1;
      setStatus(`正在准备音频 ${done} / ${segments.length}…`);
    }
  };

  try {
    await Promise.all([worker(), worker(), worker(), worker()]);
    if (token !== playToken) return;
    const built = await buildCombined(blobs);
    if (token !== playToken) return;
    segTimes = built.times;
    currentSeg = -1;
    audioEl.src = built.url;
    audioEl.loop = loopMode;
    audioEl.ontimeupdate = onTimeUpdate;
    audioEl.onended = () => {
      setPlayingUI(false);
      setStatus("诵读完毕");
      stopBgm();
      clearHighlight();
    };
    audioEl.currentTime = built.times[index];
    await audioEl.play();
    btnPlay.classList.remove("preparing");
    btnPlay.querySelector(".play-label").textContent = "停 止";
    if (bgmOn) startBgm(); // play() 成功后起步背景音乐（用户手势上下文内）
    updateMediaSession();
    cursorRaf = requestAnimationFrame(cursorTick); // 启动逐字光标
    setStatus(`正在朗读 · ${currentVoice()}`);
  } catch (err) {
    if (err.name === "AbortError") return; // 已被停止/新播放取代
    setStatus(`语音合成失败：${err.message}`, true);
    setPlayingUI(false);
    btnPlay.classList.remove("preparing");
    clearHighlight();
  }
}

/** 设置循环开关状态并同步按钮外观（供点击与定时联动共用）。 */
function setLoopMode(on) {
  loopMode = on;
  audioEl.loop = on;
  btnLoop.classList.toggle("active", on);
  btnLoop.setAttribute("aria-pressed", String(on));
}

/** 循环诵读开关：开时读完全文自动回到第一段继续；定时关闭时即无限循环。 */
btnLoop.addEventListener("click", () => {
  setLoopMode(!loopMode);
  loopAutoByTimer = false; // 用户手动干预后以手动状态为准
  savePref("loop", loopMode);
  setStatus(loopMode ? "循环诵读：开" : "循环诵读：关");
});

/** 定时停止到期：停止播放、下拉复位，并收回定时自动带开的循环。 */
function fireSleepTimer() {
  sleepEndAt = 0;
  sleepTimer = null;
  timerSelect.value = "0";
  sheetSyncFns.get(timerSelect)?.();
  if (loopAutoByTimer) {
    loopAutoByTimer = false;
    setLoopMode(false);
  }
  if (playing || inflight) {
    stopPlayback();
    setStatus("定时结束，已停止播放");
  }
}

/** 定时停止：选 30/60/90/120 分钟后到点自动停播；选"关闭"取消。 */
timerSelect.addEventListener("change", () => {
  if (sleepTimer) {
    clearTimeout(sleepTimer);
    sleepTimer = null;
  }
  const mins = Number(timerSelect.value);
  if (!mins) {
    sleepEndAt = 0;
    if (loopAutoByTimer) {
      // 定时带开的循环随"关闭"一并收回；用户手动开的循环不动
      loopAutoByTimer = false;
      setLoopMode(false);
    }
    setStatus("定时停止：关");
    return;
  }
  sleepEndAt = Date.now() + mins * 60000;
  sleepTimer = setTimeout(fireSleepTimer, mins * 60000);
  if (!loopMode) {
    setLoopMode(true); // 定时场景自动开启循环，播到点为止
    loopAutoByTimer = true;
  }
  setStatus(`定时 ${mins} 分钟后停止 · 循环已开`);
});

/** 背景音乐开关：播放中开/关即时淡入淡出；未播放时只记录状态，下次播放生效。 */
btnBgm.addEventListener("click", () => {
  bgmOn = !bgmOn;
  btnBgm.classList.toggle("active", bgmOn);
  btnBgm.setAttribute("aria-pressed", String(bgmOn));
  savePref("bgm", bgmOn);
  if (bgmOn && playing) startBgm();
  if (!bgmOn) stopBgm();
  setStatus(bgmOn ? "背景音乐：开" : "背景音乐：关");
});

/** 语速切换：直接改已合并音频的 playbackRate，立即生效。 */
rateSelect.addEventListener("change", () => {
  audioEl.playbackRate = Number(rateSelect.value);
  savePref("rate", rateSelect.value);
  setStatus(`语速：${rateSelect.options[rateSelect.selectedIndex].text}`);
});

/** 夜间模式：暗色宣纸配色，睡前诵读不刺眼。 */
btnNight.addEventListener("click", () => {
  const on = document.body.classList.toggle("night");
  btnNight.classList.toggle("active", on);
  btnNight.setAttribute("aria-pressed", String(on));
  btnNight.textContent = on ? "日间" : "夜间";
  savePref("night", on);
});

btnPlay.addEventListener("click", () => {
  if (playing || inflight) {
    stopPlayback();
    setStatus("已停止");
  } else {
    playFrom(0);
  }
});

voiceSelect.addEventListener("change", () => {
  if (playing || inflight) stopPlayback();
  savePref("voice", voiceSelect.value);
  setStatus(`已切换音色：${voiceSelect.value}，点击播放开始诵读`);
});

// 移动端设置区折叠/展开（齿轮图标按钮，桌面端不可见）
btnExpand.addEventListener("click", () => {
  const expanded = playerCard.classList.toggle("expanded");
  btnExpand.classList.toggle("open", expanded);
  btnExpand.querySelector(".expand-label").textContent = expanded ? "收起" : "设置";
  btnExpand.setAttribute("aria-expanded", String(expanded));
});

btnPrev.addEventListener("click", () => gotoPage(currentPage - 1));
btnNext.addEventListener("click", () => gotoPage(currentPage + 1));

// 手动滚轮/触摸滚动经文：记录时间，6 秒内跟读滚动让位给读者
["wheel", "touchmove"].forEach((ev) => {
  sutraEl.addEventListener(ev, () => { lastUserScroll = Date.now(); }, { passive: true });
});
// 任何滚动（含自动滚动）都刷新"回到诵读处"按钮的可见性
sutraEl.addEventListener("scroll", () => { if (playing) updateJumpNow(); }, { passive: true });
btnJumpNow.addEventListener("click", () => {
  lastUserScroll = 0;
  let active = segEls.find((el) => Number(el.dataset.index) === currentSeg);
  if (!active && currentSeg >= 0) {
    renderPage(pageOf(currentSeg)); // 当前段不在本页，先翻过去
    active = segEls.find((el) => Number(el.dataset.index) === currentSeg);
  }
  const target = active?.querySelector(".ch.cur") || active;
  target?.scrollIntoView({ behavior: "smooth", block: "center", inline: "center" });
  btnJumpNow.hidden = true;
});

sutraSelect.addEventListener("change", () => selectSutra(sutraSelect.value));

// 键盘 ← → 翻页（下拉框聚焦时不拦截）
document.addEventListener("keydown", (e) => {
  if (e.target.tagName === "SELECT") return;
  if (e.key === "ArrowLeft") gotoPage(currentPage - 1);
  if (e.key === "ArrowRight") gotoPage(currentPage + 1);
});

// ===== 字号与排版 =====
/** 应用字号档位并同步按钮高亮。 */
function setFontSize(size) {
  if (!["sm", "md", "lg"].includes(size)) return;
  document.querySelectorAll(".size-btn").forEach((b) => b.classList.toggle("active", b.dataset.size === size));
  sutraEl.classList.remove("size-sm", "size-md", "size-lg");
  sutraEl.classList.add(`size-${size}`);
}
document.querySelectorAll(".size-btn").forEach((btn) => {
  btn.addEventListener("click", () => {
    setFontSize(btn.dataset.size);
    savePref("size", btn.dataset.size);
  });
});

const mobileMQ = matchMedia("(max-width: 640px)");

btnLayout.addEventListener("click", () => {
  const vertical = sutraEl.classList.toggle("vertical");
  btnLayout.textContent = vertical ? "切换横排" : "切换竖排";
  btnLayout.classList.toggle("active", vertical);
});

// 移动端不提供竖排：窗口收窄时若处于竖排则切回横排
mobileMQ.addEventListener("change", () => {
  if (mobileMQ.matches && sutraEl.classList.contains("vertical")) {
    btnLayout.click();
  }
});

// ===== 移动端底部升起选择器：原生 select 保留为状态源，手机上改由面板选择 =====
const sheetSyncFns = new Map(); // select → 同步按钮文字的函数
let sheetEls = null; // 当前打开的面板 {mask, panel}

/** 关闭底部选择面板（若开着）。 */
function closeSheet() {
  if (!sheetEls) return;
  const { mask, panel } = sheetEls;
  sheetEls = null;
  mask.classList.remove("open");
  panel.classList.remove("open");
  setTimeout(() => { mask.remove(); panel.remove(); }, 220);
}

/** 打开底部升起面板：列出 select 全部选项，点选后同步并派发 change。 */
function openSheet(select, title) {
  closeSheet();
  const mask = document.createElement("div");
  mask.className = "sheet-mask";
  const panel = document.createElement("div");
  panel.className = "sheet-panel";
  panel.setAttribute("role", "dialog");
  panel.setAttribute("aria-label", title);
  panel.innerHTML = `<div class="sheet-grabber"></div><div class="sheet-title">${title}</div><div class="sheet-opts"></div>`;
  const opts = panel.querySelector(".sheet-opts");
  let lastGroup = null; // optgroup 分组标题（如"佛经/道家"），无分组时不渲染
  [...select.options].forEach((opt, i) => {
    const group = opt.parentElement?.tagName === "OPTGROUP" ? opt.parentElement.label : null;
    if (group && group !== lastGroup) {
      lastGroup = group;
      const gh = document.createElement("div");
      gh.className = "sheet-group";
      gh.textContent = group;
      opts.appendChild(gh);
    }
    const item = document.createElement("div");
    item.className = `sheet-opt${i === select.selectedIndex ? " sel" : ""}`;
    item.textContent = opt.textContent;
    item.setAttribute("role", "option");
    item.addEventListener("click", () => {
      select.value = opt.value;
      select.dispatchEvent(new Event("change"));
      closeSheet();
    });
    opts.appendChild(item);
  });
  const cancel = document.createElement("div");
  cancel.className = "sheet-cancel";
  cancel.textContent = "取 消";
  cancel.addEventListener("click", closeSheet);
  panel.appendChild(cancel);
  mask.addEventListener("click", closeSheet);
  document.body.appendChild(mask);
  document.body.appendChild(panel);
  sheetEls = { mask, panel };
  requestAnimationFrame(() => {
    mask.classList.add("open");
    panel.classList.add("open");
  });
}

/** 为 select 生成伪下拉按钮（仅移动端显示），点击打开底部面板。 */
function attachSheet(select, title) {
  if (!select) return;
  const btn = document.createElement("button");
  btn.type = "button";
  btn.className = "sheet-btn";
  btn.setAttribute("aria-haspopup", "dialog");
  const text = document.createElement("span");
  text.className = "sheet-btn-text";
  const sync = () => {
    text.textContent = select.options[select.selectedIndex]?.textContent || "";
  };
  sync();
  sheetSyncFns.set(select, sync);
  select.addEventListener("change", sync);
  btn.appendChild(text);
  select.insertAdjacentElement("afterend", btn);
  btn.addEventListener("click", () => openSheet(select, title));
}
attachSheet(sutraSelect, "选择经典");
attachSheet(voiceSelect, "诵读音色");
attachSheet(timerSelect, "定时停止");
attachSheet(rateSelect, "诵读语速");

// 锁屏/控制中心按键：上一段/下一段、暂停、停止
if ("mediaSession" in navigator) {
  navigator.mediaSession.setActionHandler("play", () => { if (!playing && !inflight) playFrom(Math.max(currentSeg, 0)); });
  navigator.mediaSession.setActionHandler("pause", () => stopPlayback());
  navigator.mediaSession.setActionHandler("stop", () => stopPlayback());
  navigator.mediaSession.setActionHandler("previoustrack", () => playFrom(Math.max(currentSeg - 1, 0)));
  navigator.mediaSession.setActionHandler("nexttrack", () => { if (currentSeg + 1 < segments.length) playFrom(currentSeg + 1); });
}

// ===== PWA：注册 Service Worker，使"添加到主屏幕"后无地址栏独立运行 =====
if ("serviceWorker" in navigator) {
  window.addEventListener("load", () => navigator.serviceWorker.register("/sw.js").catch(() => {}));
}

// ===== 初始化：恢复偏好（hash 锚点优先于记忆的经典/排版） =====
if (prefs.voice && [...voiceSelect.options].some((o) => o.value === prefs.voice)) voiceSelect.value = prefs.voice;
sheetSyncFns.get(voiceSelect)?.();
if (prefs.size) setFontSize(prefs.size);
if (prefs.loop) setLoopMode(true);
if (prefs.bgm) {
  bgmOn = true;
  btnBgm.classList.add("active");
  btnBgm.setAttribute("aria-pressed", "true");
}
if (prefs.rate && [...rateSelect.options].some((o) => o.value === String(prefs.rate))) {
  rateSelect.value = prefs.rate;
  audioEl.playbackRate = Number(prefs.rate);
  sheetSyncFns.get(rateSelect)?.();
}
if (prefs.night) {
  document.body.classList.add("night");
  btnNight.classList.add("active");
  btnNight.setAttribute("aria-pressed", "true");
  btnNight.textContent = "日间";
}

if (location.hash.includes("vertical") && !mobileMQ.matches) {
  btnLayout.click();
}
// URL hash 可直达某部经（如 #jingang、#daodejing），优先于记忆的经典
const hashId = location.hash.replace(/^#/, "");

/** 启动：拉经典目录清单 → 建下拉 → 选中初始经（hash > 记忆 > 第一部）。 */
(async function boot() {
  try {
    const resp = await fetch("/api/sutras");
    const data = await resp.json();
    SUTRAS.push(...(data.sutras || []));
  } catch {
    setStatus("经典目录载入失败", true);
  }
  buildSutraOptions();
  const initSutraId = SUTRAS.some((s) => s.id === hashId)
    ? hashId
    : (SUTRAS.some((s) => s.id === prefs.sutra) ? prefs.sutra : SUTRAS[0]?.id);
  if (initSutraId) selectSutra(initSutraId);
})();