MangaCircus/public/reader.js

'use strict';
/*
 * Chapter reader.
 *  - Modes: flow (all pages below each other, same width), page (one page), book (two facing pages; double pages alone).
 *  - Page zoom ("zoom" below): 1 = the page (in flow: a normal single page) exactly fits the screen.
 *    It is remembered per mode; flow for webtoons has its own value ("strip", 1 = strip as wide as the screen / its own width).
 *  - Tap zones: left/right third turns pages following the reading direction (top/bottom third in flow), the middle toggles the bars.
 *  - All pages are laid out with absolute positions computed from the image sizes the server knows, so zooming and
 *    restoring positions never depend on images having loaded.
 */
(async function () {
  const P = new URLSearchParams(location.search);
  const stage = $('#stage'), canvas = $('#canvas'), slider = $('#slider'), ver = $('#ver');
  let me, D;
  try { [me, D] = await Promise.all([api('api/me'), api('api/chapter?' + qsa({ m: P.get('m'), c: P.get('c'), v: P.get('v') }))]); }
  catch (e) { canvas.textContent = ''; canvas.append(h('p', { class: 'loading' }, e.message + ' · ', h('a', { href: './' }, 'Library'))); return; }

  const S = me.settings, rtl = D.direction === 'rtl', ttb = D.direction === 'ttb';
  const GAP = ttb ? 0 : 8, END_H = 280;
  document.title = `${D.chapter.label} · ${D.manga.title}`;

  // ---------- pages ----------
  const all = D.pages.map((p, i) => {
    const t = p.t || [], r = p.r || 0, unknown = !p.w || !p.h;
    const w = unknown ? (t.includes('double') ? 2000 : 1000) : p.w, hh = unknown ? 1414 : p.h;
    const dw = r % 180 ? hh : w, dh = r % 180 ? w : hh; // size as displayed (after rotation)
    return { i, u: p.u, r, w: dw, a: dw / dh, unknown, cover: t.includes('cover'), extra: t.includes('extra'), wide: t.includes('double') || dw > dh };
  });
  let list = all.filter(p => !(S.skipExtras && p.extra) && !(S.skipCovers && p.cover));
  if (!list.length) list = all;
  const median = xs => (xs.length ? xs.sort((x, y) => x - y)[xs.length >> 1] : 0);
  const refA = median(list.filter(p => !p.wide).map(p => p.a)) || 0.7; // aspect ratio of a normal single page
  const refW = median(list.map(p => p.w)) || 800; // natural width of a webtoon strip
  const solo = p => p.wide || p.cover; // shown alone in book mode

  // ---------- state ----------
  const compatible = ttb ? ['flow'] : ['flow', 'page', 'book'];
  const intended = S.startMode === 'last' ? S.lastMode : S.startMode;
  let mode = S.adapt && !compatible.includes(intended) ? compatible[0] : intended;
  if (!['flow', 'page', 'book'].includes(mode)) mode = compatible[0];

  let cur = 0, atEnd = false, done = !!(D.progress && D.progress.done), bars = true, barsAt = 0;
  let spreads = [], spreadIdx = 0, shown = [], els = [], boxes = [], endEl = null, lastW = 0, lastH = 0;
  const shift = new Set(D.progress && D.progress.v === D.version ? D.progress.shift : []);
  const zkey = () => (mode === 'flow' && ttb ? 'strip' : mode);
  const zoom = () => S.zoom[zkey()] || 1;

  const pr = D.progress;
  if (pr && !(pr.done && pr.p >= pr.n - 1)) {
    const p = pr.v === D.version || !pr.n ? pr.p : Math.round((pr.p / pr.n) * all.length);
    const k = list.findIndex(x => x.i >= p);
    cur = k < 0 ? list.length - 1 : k;
  }

  // Book mode: pages pair up inside each run of single pages. Runs restart after every double page / cover,
  // so one missing pair never shifts the rest of the chapter. "Shift" makes a run start with a lone page.
  function computeSpreads() {
    const out = [];
    for (let i = 0; i < list.length;) {
      if (solo(list[i])) { out.push([i++]); continue; }
      let j = i, k = i;
      while (j < list.length && !solo(list[j])) j++;
      if (shift.has(list[i].i)) out.push([k++]);
      for (; k < j; k += 2) out.push(k + 1 < j ? [k, k + 1] : [k]);
      i = j;
    }
    return out;
  }
  const runStart = k => { while (k > 0 && !solo(list[k - 1])) k--; return k; };

  // ---------- rendering ----------
  const io = window.IntersectionObserver
    ? new IntersectionObserver(entries => {
      for (const e of entries) if (e.isIntersecting) { setSrc(e.target, e.target._p.u); io.unobserve(e.target); }
    }, { root: stage, rootMargin: '150% 50%' })
    : null;

  // Page/book mode: preloaded images are downloaded *and decoded* ahead of time and then shown as the very same
  // elements, so a page turn swaps pictures within one frame instead of flashing an empty box.
  const pool = new Map();
  function pooled(url, priority) {
    let img = pool.get(url);
    if (img) pool.delete(url);
    else {
      img = new Image();
      img.decoding = 'async';
      img.fetchPriority = priority;
      img.src = url;
      if (img.decode) img.decode().catch(() => {});
    }
    pool.set(url, img); // most recently used last
    while (pool.size > 12) pool.delete(pool.keys().next().value);
    return img;
  }
  function preloadAround() {
    const ahead = mode === 'page' ? [cur + 1, cur + 2, cur + 3, cur - 1]
      : [].concat(spreads[spreadIdx + 1] || [], spreads[spreadIdx + 2] || [], spreads[spreadIdx - 1] || []);
    for (const k of ahead) if (list[k]) pooled(list[k].u, 'low');
  }

  // A spinner shows (after a short delay, see CSS) while a page is still loading, a message if it failed.
  function watch(el) {
    const img = el.firstChild, p = el._p;
    const state = () => {
      el.classList.toggle('loading', !!img.getAttribute('src') && !img.complete);
      el.classList.toggle('failed', img.complete && !!img.getAttribute('src') && !img.naturalWidth);
    };
    img.onload = () => {
      state();
      if (p.unknown && img.naturalWidth) {
        const w = p.r % 180 ? img.naturalHeight : img.naturalWidth, hh = p.r % 180 ? img.naturalWidth : img.naturalHeight;
        Object.assign(p, { unknown: false, w, a: w / hh, wide: p.wide || w > hh });
        relayout();
      }
    };
    img.onerror = state;
    state();
  }
  function setSrc(el, url) { el.firstChild.src = url; watch(el); }

  function pageEl(p, lazy) {
    const img = lazy ? h('img', { decoding: 'async' }) : pooled(p.u, 'high');
    img.alt = '';
    img.draggable = false;
    img.style.cssText = p.r ? `transform: translate(-50%, -50%) rotate(${p.r}deg)` : '';
    if (!lazy) img.decoding = 'sync'; // paint together with the page turn (it is decoded already when preloaded)
    const el = h('div', { class: 'pg' + (p.r ? ' rot' : '') }, img);
    el._p = p;
    if (!lazy) watch(el);
    else if (io) io.observe(el);
    else setSrc(el, p.u);
    return el;
  }

  function endCard() {
    const n = D.next;
    return h('div', { class: 'end' }, h('div', { class: 'endbox' },
      h('div', { class: 'muted' }, 'End of ' + D.chapter.label + (D.chapter.title ? ' · ' + D.chapter.title : '')),
      n ? h('a', { class: 'btn primary', href: readUrl(D.manga.id, n.id), onclick: () => saveProgress(true) }, `Next: ${n.label}${n.title ? ' · ' + n.title : ''} ›`)
        : h('div', {}, 'You are up to date.'),
      h('a', { class: 'btn', href: mangaUrl(D.manga.id) }, 'Back to ' + D.manga.title)));
  }

  function build() {
    if (io) io.disconnect();
    canvas.textContent = '';
    canvas.className = mode + (ttb ? ' ttb' : '');
    els = []; shown = []; endEl = null;
    if (mode === 'flow') {
      els = list.map(p => canvas.appendChild(pageEl(p, true)));
      endEl = canvas.appendChild(endCard());
    } else if (atEnd) {
      endEl = canvas.appendChild(endCard());
    } else {
      shown = mode === 'page' ? [cur] : spreads[spreadIdx];
      els = shown.map(k => canvas.appendChild(pageEl(list[k])));
      // The pages on screen get the bandwidth first, then the next ones are fetched.
      const token = ++buildToken, waiting = els.map(el => el.firstChild).filter(img => !img.complete);
      Promise.all(waiting.map(img => new Promise(done => {
        img.addEventListener('load', done, { once: true });
        img.addEventListener('error', done, { once: true });
      }))).then(() => { if (token === buildToken) preloadAround(); });
    }
    layout();
  }
  let buildToken = 0;

  // Scrollbars appear/disappear with the content size and change the viewport, so repeat until it is stable.
  function layout() {
    for (let pass = 0; pass < 3; pass++) {
      const vw = stage.clientWidth, vh = stage.clientHeight;
      layoutFor(vw, vh);
      if (stage.clientWidth === vw && stage.clientHeight === vh) break;
    }
  }
  function layoutFor(vw, vh) {
    const z = zoom();
    let cw = vw, ch = vh;
    boxes = [];
    if (mode === 'flow') {
      // Every page gets the width of a normal single page; wide pages keep that height but never get wider than the screen.
      const W = (ttb ? Math.min(vw, refW) : Math.min(vw, vh * refA)) * z;
      const ws = list.map(p => (p.wide && !ttb ? Math.min((W * p.a) / refA, Math.max(vw, W)) : W));
      cw = Math.max(vw, ...ws);
      let y = 0;
      ws.forEach((w, k) => { boxes.push({ x: (cw - w) / 2, y, w, h: w / list[k].a }); y += w / list[k].a + GAP; });
      endEl.style.top = y + 'px';
      endEl.style.height = END_H + 'px';
      ch = y + END_H;
    } else if (shown.length) {
      const sum = shown.reduce((s, k) => s + list[k].a, 0), H = Math.min(vh, vw / sum) * z, W = H * sum;
      cw = Math.max(vw, W); ch = Math.max(vh, H);
      const y = (ch - H) / 2, order = shown.map((k, j) => j);
      if (rtl) order.reverse(); // right-to-left: the first page of a pair sits on the right
      let x = (cw - W) / 2;
      for (const j of order) { boxes[j] = { x, y, w: H * list[shown[j]].a, h: H }; x += boxes[j].w; }
    }
    canvas.style.width = cw + 'px';
    canvas.style.height = ch + 'px';
    els.forEach((el, j) => place(el, boxes[j]));
    stage.classList.toggle('pan', cw > vw + 1 || (mode === 'flow' ? z > 1.01 : ch > vh + 1));
    lastW = vw; lastH = vh;
  }

  function place(el, b) {
    const s = el.style, x = Math.round(b.x), y = Math.round(b.y), w = Math.round(b.x + b.w) - x, hh = Math.round(b.y + b.h) - y;
    s.left = x + 'px'; s.top = y + 'px'; s.width = w + 'px'; s.height = hh + 'px';
    if (el._p.r) {
      const im = el.firstChild.style, turned = el._p.r % 180;
      im.width = (turned ? hh : w) + 'px';
      im.height = (turned ? w : hh) + 'px';
    }
  }

  function flowIndexAt(y) {
    let lo = 0, hi = boxes.length - 1;
    while (lo < hi) { const mid = (lo + hi + 1) >> 1; if (boxes[mid].y <= y) lo = mid; else hi = mid - 1; }
    return lo;
  }
  function union() {
    const x = Math.min(...boxes.map(b => b.x));
    return { x, y: boxes[0].y, w: Math.max(...boxes.map(b => b.x + b.w)) - x, h: boxes[0].h };
  }
  // Remember which point of which page is under (cx, cy) and put it back there after a re-layout.
  function anchor(cx, cy) {
    if (!boxes.length) return null;
    const X = stage.scrollLeft + cx, Y = stage.scrollTop + cy, k = mode === 'flow' ? flowIndexAt(Y) : -1, b = k < 0 ? union() : boxes[k];
    return { k, fx: (X - b.x) / b.w, fy: (Y - b.y) / b.h };
  }
  function restore(a, cx, cy) {
    if (!a || !boxes.length) return;
    const b = a.k < 0 ? union() : boxes[a.k];
    stage.scrollLeft = b.x + a.fx * b.w - cx;
    stage.scrollTop = b.y + a.fy * b.h - cy;
    barsAt = stage.scrollTop;
  }
  function relayout() { const a = anchor(lastW / 2, lastH / 2); layout(); restore(a, lastW / 2, lastH / 2); }

  // ---------- zoom ----------
  let zoomTimer = 0;
  function setZoom(z, cx = stage.clientWidth / 2, cy = stage.clientHeight / 2) {
    z = Math.min(6, Math.max(0.2, z));
    if (Math.abs(z - 1) < 0.03) z = 1; // easy to get back to "fit"
    if (Math.abs(z - zoom()) < 0.001) return;
    const a = anchor(cx, cy);
    S.zoom[zkey()] = z;
    layout();
    restore(a, cx, cy);
    toast(Math.round(z * 100) + '%');
    updateUI();
    clearTimeout(zoomTimer);
    zoomTimer = setTimeout(() => api('api/settings', { zoom: S.zoom }).catch(() => {}), 800);
  }

  // Ctrl + wheel (and touchpad pinch, which browsers report the same way) zooms the pages, not the page controls.
  stage.addEventListener('wheel', e => {
    if (!e.ctrlKey) return;
    e.preventDefault();
    setZoom(zoom() * Math.exp(-e.deltaY * (e.deltaMode === 1 ? 0.05 : 0.0025)), e.clientX, e.clientY);
  }, { passive: false });

  // Touch: two fingers zoom, a quick horizontal swipe turns the page (page/book mode, when not zoomed in).
  let pinch = null, swipe = null, pinchRaf = 0, pinchNext = null;
  const pinchApply = () => { pinchRaf = 0; if (pinchNext) setZoom(...pinchNext); pinchNext = null; };
  const dist = t => Math.hypot(t[0].clientX - t[1].clientX, t[0].clientY - t[1].clientY);
  stage.addEventListener('touchstart', e => {
    const t = e.touches;
    if (t.length === 2) { pinch = { d: dist(t), z: zoom() }; swipe = null; }
    else if (t.length === 1) swipe = { x: t[0].clientX, y: t[0].clientY, t: Date.now() };
  }, { passive: true });
  stage.addEventListener('touchmove', e => {
    if (!pinch || e.touches.length !== 2) return;
    e.preventDefault();
    const t = e.touches;
    pinchNext = [pinch.z * dist(t) / pinch.d, (t[0].clientX + t[1].clientX) / 2, (t[0].clientY + t[1].clientY) / 2];
    pinchRaf = pinchRaf || requestAnimationFrame(pinchApply);
  }, { passive: false });
  stage.addEventListener('touchend', e => {
    if (e.touches.length < 2) { if (pinchNext) pinchApply(); pinch = null; }
    const s = swipe;
    swipe = null;
    if (!s || mode === 'flow' || e.touches.length) return;
    const t = e.changedTouches[0], dx = t.clientX - s.x, dy = t.clientY - s.y;
    if (Math.abs(dx) < 50 || Math.abs(dx) < 2 * Math.abs(dy) || Date.now() - s.t > 800) return;
    if (stage.scrollWidth > stage.clientWidth + 1) return; // zoomed in: the finger pans instead
    ((dx > 0) === rtl ? next : prev)();
  });
  // Safari reports pinches as gesture events; without this it would zoom the whole page.
  let gestureZoom = 1;
  stage.addEventListener('gesturestart', e => { e.preventDefault(); gestureZoom = zoom(); });
  stage.addEventListener('gesturechange', e => { e.preventDefault(); if (!pinch) setZoom(gestureZoom * e.scale, e.clientX, e.clientY); });

  // Mouse: drag to move a zoomed page around; a click without dragging uses the tap zones.
  let drag = null, dragged = false;
  stage.addEventListener('pointerdown', e => {
    if (e.pointerType === 'mouse' && e.button === 0) drag = { x: e.clientX, y: e.clientY, l: stage.scrollLeft, t: stage.scrollTop, moved: false };
  });
  addEventListener('pointermove', e => {
    if (!drag) return;
    const dx = e.clientX - drag.x, dy = e.clientY - drag.y;
    if (!drag.moved && Math.abs(dx) + Math.abs(dy) < 6) return;
    drag.moved = true;
    stage.classList.add('drag');
    stage.scrollLeft = drag.l - dx;
    stage.scrollTop = drag.t - dy;
  });
  addEventListener('pointerup', () => {
    if (drag && drag.moved) { dragged = true; setTimeout(() => { dragged = false; }, 0); }
    drag = null;
    stage.classList.remove('drag');
  });

  // Outside the pages: toggle the controls. On a page: the outer 35 % of the visible page area turn pages
  // (top/bottom in flow), the middle toggles the controls (needed when a zoomed page fills the whole screen).
  stage.addEventListener('click', e => {
    if (dragged || e.target.closest('a, button, select, input')) return;
    const onPage = e.target.closest('.pg'), vw = stage.clientWidth;
    if (!onPage && !(atEnd && mode !== 'flow')) return toggleBars();
    if (mode === 'flow') {
      const fy = e.clientY / stage.clientHeight;
      return fy < 0.35 ? prev() : fy > 0.65 ? next() : toggleBars();
    }
    let left = 0, right = vw;
    if (!atEnd) {
      const rects = els.map(el => el.getBoundingClientRect());
      left = Math.max(0, Math.min(...rects.map(r => r.left)));
      right = Math.min(vw, Math.max(...rects.map(r => r.right)));
    }
    const fx = (e.clientX - left) / (right - left);
    if (fx < 0.35) (rtl ? next : prev)();
    else if (fx > 0.65) (rtl ? prev : next)();
    else toggleBars();
  });

  addEventListener('keydown', e => {
    if ((e.target.closest && e.target.closest('input, select, textarea')) || e.ctrlKey || e.metaKey || e.altKey) return;
    const k = e.key;
    if (k === 'ArrowLeft' || k === 'ArrowRight') { e.preventDefault(); (k === (rtl ? 'ArrowLeft' : 'ArrowRight') ? next : prev)(); }
    else if ((k === ' ' || k === 'PageDown') && mode !== 'flow') { e.preventDefault(); (e.shiftKey ? prev : next)(); }
    else if (k === 'PageUp' && mode !== 'flow') { e.preventDefault(); prev(); }
    else if (k === '+' || k === '=') setZoom(zoom() * 1.15);
    else if (k === '-') setZoom(zoom() / 1.15);
    else if (k === '0') setZoom(1);
    else if (k === 'm' || k === 'Escape') toggleBars();
    else if (k === 'f') toggleFullscreen();
  });

  let scrollRaf = 0;
  stage.addEventListener('scroll', () => {
    if (mode !== 'flow' || scrollRaf) return;
    scrollRaf = requestAnimationFrame(() => {
      scrollRaf = 0;
      cur = flowIndexAt(stage.scrollTop + stage.clientHeight * 0.3);
      // Scrolling (up or down) only ever hides the bars; they come back with a tap in the middle.
      if (bars && Math.abs(stage.scrollTop - barsAt) > 100) autoHide();
      moved();
    });
  });

  let resizeRaf = 0;
  addEventListener('resize', () => { resizeRaf = resizeRaf || requestAnimationFrame(() => { resizeRaf = 0; relayout(); }); });

  // ---------- navigation ----------
  function next() {
    if (mode === 'flow') return flowStep(1);
    if (atEnd) return goChapter(D.next);
    if (mode === 'page' ? cur >= list.length - 1 : spreadIdx >= spreads.length - 1) atEnd = true;
    else if (mode === 'page') cur++;
    else cur = spreads[++spreadIdx][0];
    turned();
  }
  function prev() {
    if (mode === 'flow') return flowStep(-1);
    if (atEnd) atEnd = false;
    else if (mode === 'page' ? cur === 0 : spreadIdx === 0) return toast('First page');
    else if (mode === 'page') cur--;
    else cur = spreads[--spreadIdx][0];
    turned();
  }
  function turned() { build(); toStart(); autoHide(); moved(); }
  function toStart() { stage.scrollTop = 0; stage.scrollLeft = rtl ? stage.scrollWidth : 0; barsAt = 0; }
  function goChapter(c) {
    if (!c) return toast('You are up to date');
    saveProgress(true);
    location.href = readUrl(D.manga.id, c.id);
  }
  // Flow: jump to the top of the next page, but never further than ~one screen.
  function flowStep(dir) {
    const st = stage.scrollTop, vh = stage.clientHeight;
    if (dir > 0 && st + vh >= stage.scrollHeight - 2) return goChapter(D.next);
    let t;
    if (ttb) t = st + dir * vh * 0.85; // webtoon slices are arbitrary cuts: just scroll
    else if (dir > 0) { const b = boxes.find(b => b.y > st + 2); t = b ? Math.min(b.y, st + vh * 0.9) : st + vh * 0.9; }
    else { let b = null; for (const x of boxes) { if (x.y < st - 2) b = x; else break; } t = b ? Math.max(b.y, st - vh * 0.9) : 0; }
    stage.scrollTo({ top: t, behavior: 'smooth' });
  }
  function goTo(k) {
    atEnd = false;
    if (mode === 'flow') { stage.scrollTop = boxes[k].y; barsAt = stage.scrollTop; cur = k; return moved(); }
    if (mode === 'book') { spreadIdx = spreads.findIndex(s => s.includes(k)); cur = spreads[spreadIdx][0]; }
    else cur = k;
    build(); toStart(); moved();
  }

  function setMode(m, byUser) {
    mode = m; atEnd = false;
    if (mode === 'book') {
      spreads = computeSpreads();
      spreadIdx = Math.max(0, spreads.findIndex(s => s.includes(cur)));
      cur = spreads[spreadIdx][0];
    }
    build();
    if (mode === 'flow') {
      stage.scrollTop = boxes[cur].y;
      stage.scrollLeft = (stage.scrollWidth - stage.clientWidth) / 2;
      barsAt = stage.scrollTop;
    } else toStart();
    // Only a click changes the remembered mode, never an automatic switch for incompatible content.
    if (byUser) { S.lastMode = m; api('api/settings', { lastMode: m }).catch(() => {}); }
    moved();
  }

  function toggleShift() {
    const k = shown[0];
    if (k === undefined || solo(list[k])) return toast('This page is shown alone anyway');
    const s = list[runStart(k)].i;
    if (shift.has(s)) shift.delete(s);
    else shift.add(s);
    spreads = computeSpreads();
    spreadIdx = spreads.findIndex(sp => sp.includes(k));
    cur = spreads[spreadIdx][0];
    build(); toStart(); moved();
    toast(shift.has(s) ? 'Pairs shifted by one page' : 'Pairs back to normal');
  }

  // ---------- bars, progress ----------
  function setBars(on) {
    // Stop a running smooth scroll first, otherwise it would hide the bars again right away.
    if (on) stage.scrollTo({ left: stage.scrollLeft, top: stage.scrollTop });
    bars = on;
    document.body.classList.toggle('nobars', !on);
    barsAt = stage.scrollTop;
  }
  function toggleBars() { setBars(!bars); }
  // Reading hides the bars. The first time (per device and per kind of mode) say how to get them back.
  function autoHide() {
    if (!bars) return;
    setBars(false);
    const key = mode === 'flow' ? 'hint.flow' : 'hint.paged';
    if (store.get(key)) return;
    store.set(key, '1');
    toast(mode === 'flow' ? 'Controls hidden · tap the middle of the screen or beside the pages to show them'
      : 'Controls hidden · tap the middle of the page or beside it to show them', 3500);
  }

  let toastTimer = 0;
  function toast(msg, ms = 900) {
    const t = $('#toast');
    t.textContent = msg;
    t.classList.add('show');
    clearTimeout(toastTimer);
    toastTimer = setTimeout(() => t.classList.remove('show'), ms);
  }

  const modeBtns = [...document.querySelectorAll('#modes button')];
  function updateUI() {
    const n = list.length;
    $('#pageno').textContent = atEnd ? 'end' : (shown.length === 2 ? `${cur + 1}-${cur + 2}` : cur + 1) + ' / ' + n;
    slider.max = n;
    slider.value = cur + 1;
    for (const b of modeBtns) {
      b.classList.toggle('on', b.dataset.mode === mode);
      b.classList.toggle('meh', !compatible.includes(b.dataset.mode));
    }
    const sh = $('#shift');
    sh.hidden = mode !== 'book';
    sh.classList.toggle('on', shown.length > 0 && !solo(list[shown[0]]) && shift.has(list[runStart(shown[0])].i));
    $('#zoom').textContent = Math.round(zoom() * 100) + '%';
  }

  let saveTimer = 0;
  function moved() {
    if (mode === 'flow') {
      const b = boxes[boxes.length - 1];
      if (b && stage.scrollTop + stage.clientHeight >= b.y + b.h - 4) { done = true; cur = list.length - 1; }
    } else if (atEnd || (mode === 'page' ? cur === list.length - 1 : spreadIdx === spreads.length - 1)) done = true;
    updateUI();
    clearTimeout(saveTimer);
    saveTimer = setTimeout(saveProgress, 700);
  }
  function saveProgress(keepalive) {
    clearTimeout(saveTimer);
    const body = JSON.stringify({ m: D.manga.id, c: D.chapter.id, v: D.version, p: list[cur].i, n: all.length, done, shift: [...shift] });
    fetch('api/progress', { method: 'POST', keepalive: !!keepalive, headers: { 'Content-Type': 'application/json' }, body }).catch(() => {});
  }
  addEventListener('pagehide', () => saveProgress(true));

  // ---------- controls ----------
  $('#title').textContent = D.manga.title;
  // Chapter picker: every chapter of the manga, grouped by book when there is more than one.
  const chsel = $('#chsel'), groups = {};
  for (const b of D.books) {
    groups[b.key] = D.books.length > 1 ? chsel.appendChild(h('optgroup', { label: b.label + (b.title ? ' · ' + b.title : '') })) : chsel;
  }
  for (const c of D.chapters) {
    groups[c.book].append(h('option', { value: c.id }, `${c.label}${c.title ? ' · ' + c.title : ''}${c.extra ? ' (extra)' : ''}${c.done ? ' ✓' : ''}`));
  }
  chsel.value = D.chapter.id;
  chsel.onchange = () => { saveProgress(true); location.href = readUrl(D.manga.id, chsel.value); };
  $('#back').href = mangaUrl(D.manga.id);
  for (const [id, c] of [['#prevch', D.prev], ['#nextch', D.next]]) {
    const a = $(id);
    if (c) { a.href = readUrl(D.manga.id, c.id); a.title = c.label + (c.title ? ' · ' + c.title : ''); a.onclick = () => saveProgress(true); }
    else a.classList.add('disabled');
  }
  for (const v of D.versions) ver.append(h('option', { value: v.id }, (v.source || v.id) + (v.score ? ` (${v.score > 0 ? '+' : ''}${v.score})` : '')));
  ver.value = D.version;
  ver.hidden = D.versions.length < 2;
  ver.onchange = () => { saveProgress(true); location.href = readUrl(D.manga.id, D.chapter.id, ver.value); };
  for (const b of modeBtns) b.onclick = () => { if (b.dataset.mode !== mode) setMode(b.dataset.mode, true); };
  $('#shift').onclick = toggleShift;
  $('#zoom').onclick = () => setZoom(1);
  slider.dir = rtl ? 'rtl' : 'ltr';
  slider.addEventListener('input', () => goTo(+slider.value - 1));
  function toggleFullscreen() {
    if (!document.fullscreenEnabled) return;
    if (document.fullscreenElement) document.exitFullscreen();
    else document.documentElement.requestFullscreen().catch(() => {});
  }
  $('#fs').hidden = !document.fullscreenEnabled;
  $('#fs').onclick = toggleFullscreen;
  // Keep keyboard focus on the pages so Space/arrows never "press" the last clicked button again.
  for (const bar of [$('#top'), $('#bot')]) bar.addEventListener('click', e => { if (e.target.closest('button')) stage.focus({ preventScroll: true }); });

  setMode(mode, false);
  stage.focus({ preventScroll: true });
  setBars(true);
})();