diora-web/static/js/app/66-pdf-paginated.js

'use strict';

// ---------------------------------------------------------------------------
// PDF page by page (phones and e-readers by default; "Seiten" in the PDF panel):
// one page at a time, cropped to its text so the letters are as large as the
// screen allows, the next one drawn ahead for the turn. A tap on the left or
// right turns (the middle shows the bars), so do a swipe, the arrow keys,
// Space, PageUp/PageDown and the mouse wheel. Every page goes through
// _pdfDraw (58-pdf.js).
// ---------------------------------------------------------------------------

// A page nearly empty (only its number) would be zoomed to fill the screen with one digit:
// at most this many times the size the whole page would have.
const PDF_CROP_MAX = 2.5;
const PDF_CROP_PAD = 12;

let _pdfTurnSaveTimer = 0;
let _pdfWheelSum = 0;
let _pdfWheelAt = 0;
let _touchStartY = 0;

function enterPdfPaginatedMode() {
  const contentEl = $('reader-content');
  if (!contentEl) return;
  contentEl.classList.add('pdf-paginated');
  contentEl.style.overflow = 'hidden';
  const pdfVp = document.getElementById('pdf-viewport');
  if (pdfVp) pdfVp.style.zoom = '';
  // From scrolling: the drawing near the view stops, the pages are this mode's now.
  const v = _pdfView;
  if (v && v.observer) { v.observer.disconnect(); v.observer = null; v.queue.clear(); }
  contentEl.addEventListener('click', _pdfPaginatedClick);
  contentEl.addEventListener('wheel', _pdfPaginatedWheel, {passive: false});
  _pdfShowPage(pdfCurrentPage);
}

/** Back to scrolling, at [page] (the one shown now). */
function exitPdfPaginatedMode(page) {
  const contentEl = $('reader-content');
  if (!contentEl) return;
  contentEl.classList.remove('pdf-paginated');
  contentEl.style.overflow = '';
  contentEl.removeEventListener('click', _pdfPaginatedClick);
  contentEl.removeEventListener('wheel', _pdfPaginatedWheel);
  reRenderPdf(page || pdfCurrentPage);
}

function _pdfPaginatedClick(e) {
  if (e.target.closest('a, button, input')) return;
  // Text just selected (the text layer): that tap wasn't a turn.
  const sel = window.getSelection();
  if (sel && !sel.isCollapsed) return;
  const r = e.currentTarget.getBoundingClientRect();
  const x = e.clientX - r.left;
  const dir = x < r.width * 0.4 ? -1 : x > r.width * 0.6 ? 1 : 0;
  if (!dir) return;   // the middle: the bars come or go (62-reader.js)
  // A turn is a turn only: not also the bars.
  e.stopPropagation();
  pdfGoToPage(pdfCurrentPage + dir);
}

function _pdfPaginatedWheel(e) {
  if (e.ctrlKey) return;   // the browser's zoom
  e.preventDefault();
  const now = Date.now();
  if (now - _pdfWheelAt > 400) _pdfWheelSum = 0;
  _pdfWheelAt = now;
  _pdfWheelSum += e.deltaY;
  if (Math.abs(_pdfWheelSum) < 60) return;
  const dir = _pdfWheelSum > 0 ? 1 : -1;
  _pdfWheelSum = 0;
  _pdfWheelAt = now + 250;   // one turn per flick of the wheel
  pdfGoToPage(pdfCurrentPage + dir);
}

function _pdfTouchStart(e) {
  if (e.touches.length === 2) {
    const dx = e.touches[0].clientX - e.touches[1].clientX;
    const dy = e.touches[0].clientY - e.touches[1].clientY;
    _pinchStartDist = Math.hypot(dx, dy);
    _pinchStartZoom = readerSettings.pdfZoom;
    _isPinching = true;
    const ce = $('reader-content');
    if (ce) ce.classList.add('pinch-active');
  } else {
    _touchStartX = e.touches[0].clientX;
    _touchStartY = e.touches[0].clientY;
    _isPinching = false;
  }
}

function _pdfTouchMove(e) {
  if (e.touches.length !== 2 || !_isPinching) return;
  e.preventDefault();
  const dx = e.touches[0].clientX - e.touches[1].clientX;
  const dy = e.touches[0].clientY - e.touches[1].clientY;
  const dist = Math.hypot(dx, dy);
  if (_pinchStartDist === 0) return;
  const liveZoom = Math.max(50, Math.min(200, _pinchStartZoom * (dist / _pinchStartDist)));
  const vp = document.getElementById('pdf-viewport');
  if (vp) vp.style.zoom = liveZoom / 100;
}

function _pdfTouchEnd(e) {
  if (_isPinching) {
    _isPinching = false;
    const ce = $('reader-content');
    if (ce) ce.classList.remove('pinch-active');
    const vp = document.getElementById('pdf-viewport');
    const liveZoom = vp && vp.style.zoom ? parseFloat(vp.style.zoom) * 100 : readerSettings.pdfZoom;
    // The live zoom was only a preview: the page is drawn anew at the new size.
    if (vp) vp.style.zoom = '';
    const snapped = Math.max(50, Math.min(200, Math.round(liveZoom / 10) * 10));
    applyPdfZoom(snapped);
    return;
  }
  if (!readerSettings.pdfPaginated || !e.changedTouches.length) return;
  const dx = e.changedTouches[0].clientX - _touchStartX;
  const dy = e.changedTouches[0].clientY - _touchStartY;
  // Sideways, clearly: a slanted scroll is not a turn.
  if (Math.abs(dx) < 50 || Math.abs(dx) < Math.abs(dy) * 1.5) return;
  // Dragging a selection's handles (the text layer) isn't a swipe.
  const sel = window.getSelection();
  if (sel && !sel.isCollapsed) return;
  pdfGoToPage(pdfCurrentPage + (dx > 0 ? -1 : 1));
}

/** The page number the reader shows (header input) follows the page. */
function _pdfSetCurrentPage(n) {
  pdfCurrentPage = n;
  const input = $('reader-progress-input');
  if (input && currentPdfDoc && document.activeElement !== input) input.value = pdfPageLabel(n);
  // With the book's own page numbers: which page of the file it is beside them.
  const suffix = $('reader-progress-suffix');
  if (suffix && currentPdfDoc && pdfTotalPages) {
    suffix.textContent = _pdfLabels ? `(${n} / ${pdfTotalPages})` : `/ ${pdfTotalPages}`;
    if (input) input.setAttribute('inputmode', _pdfLabels ? 'text' : 'decimal');
  }
}

/**
 * Go to page [n], scrolling or page by page: the table of contents, the page
 * number in the header, bookmarks, keys and the app's "Zu Seite springen".
 */
function pdfGoToPage(n) {
  if (!currentPdfDoc) return;
  n = Math.max(1, Math.min(pdfTotalPages, n | 0));
  const contentEl = $('reader-content');
  if (!contentEl) return;
  if (!readerSettings.pdfPaginated) {
    const target = contentEl.querySelector(`#pdf-page-${n}`);
    if (target) {
      if (typeof _suppressScrollJumpDetect === 'function') _suppressScrollJumpDetect();
      contentEl.scrollTop += target.getBoundingClientRect().top - contentEl.getBoundingClientRect().top - 8;
    }
    _pdfSetCurrentPage(n);
    return;
  }
  if (n === pdfCurrentPage && _pdfView && _pdfView.shown === n) return;
  _pdfShowPage(n);
  _pdfTurned();
}

// A turn is reading: the place is saved soon (not only by the 10 s timer), and e-readers
// get their refresh (native-eink.js listens).
function _pdfTurned() {
  if (typeof _noteReaderInteraction === 'function') _noteReaderInteraction();
  clearTimeout(_pdfTurnSaveTimer);
  _pdfTurnSaveTimer = setTimeout(() => { if (currentPdfDoc) saveReaderProgress(); }, 1500);
  try { window.dispatchEvent(new CustomEvent('diora-pdf-turn', {detail: {page: pdfCurrentPage}})); } catch (e) {}
}

/** Show page [n] alone, cropped; draw the next one ahead and let those far away go. */
async function _pdfShowPage(n) {
  const v = _pdfView;
  if (!v || !v.entries.length) return;
  n = Math.max(1, Math.min(v.entries.length, n));
  _pdfSetCurrentPage(n);
  v.shown = n;
  const token = ++v.showToken;
  v.entries.forEach(e => { e.wrapper.style.display = e.num === n ? '' : 'none'; });
  try {
    await _pdfFitPage(v, v.entries[n - 1]);
    if (token !== v.showToken || v.stopped) return;
    if (n < v.entries.length) await _pdfFitPage(v, v.entries[n], true);
    if (token !== v.showToken || v.stopped) return;
    if (n > 1 && !v.entries[n - 2].drawn) await _pdfFitPage(v, v.entries[n - 2], true);
  } catch (err) {
    console.warn('PDF page', n, err);
  }
  if (token !== v.showToken || v.stopped) return;
  v.entries.forEach(e => { if (Math.abs(e.num - n) > 2 && (e.drawn || e.task)) _pdfLetGo(e, v.pdf); });
}

/**
 * Page [e] sized to the screen by its text (its ink, for scans): drawn when the size differs,
 * then placed so the text is centred. [ahead]: for the next turn, not shown yet.
 */
async function _pdfFitPage(v, e, ahead) {
  const contentEl = v.contentEl;
  const page = await v.pdf.getPage(e.num);
  if (v.stopped) return;
  const natural = page.getViewport({scale: 1});
  let box = _pdfPageTextBoxCache[e.num];
  if (!box) {
    box = await _computePdfTextBox(page, natural);
    _pdfPageTextBoxCache[e.num] = box;
  }
  if (v.stopped) return;
  const W = contentEl.clientWidth;
  const H = contentEl.clientHeight;
  const bw = Math.max(1, box.x2 - box.x1);
  const bh = Math.max(1, box.y2 - box.y1);
  const fitBox = Math.min((W - PDF_CROP_PAD * 2) / bw, (H - PDF_CROP_PAD * 2) / bh);
  const fitPage = Math.min((W - PDF_CROP_PAD * 2) / natural.width, (H - PDF_CROP_PAD * 2) / natural.height);
  const scale = Math.max(0.1, Math.min(fitBox, fitPage * PDF_CROP_MAX)) * (readerSettings.pdfZoom / 100);
  if (!e.drawn || Math.abs(scale - e.drawn) / e.drawn > 0.05) {
    if (!await _pdfDraw(e, page, scale)) return;
  }
  // Centre the text box (at the scale it was drawn with).
  const s = e.drawn;
  const offsetX = (W - s * bw) / 2 - s * box.x1;
  const offsetY = (H - s * bh) / 2 - s * box.y1;
  e.inner.style.transform = `translate(${offsetX}px, ${offsetY}px)`;
  e.inner.style.transformOrigin = '0 0';
  e.wrapper.style.overflow = 'hidden';
  e.wrapper.style.width = W + 'px';
  e.wrapper.style.height = H + 'px';
  if (!ahead && v.shown === e.num) e.wrapper.style.display = '';
}

/**
 * Where the page's content is, in the page's own top-down coordinates at scale 1 (as
 * getViewport gives them, so turned pages and odd media boxes come out right): its text,
 * or — a scan without text — what isn't white on a small drawing of it.
 */
async function _computePdfTextBox(page, natural) {
  const pageW = natural.width, pageH = natural.height;
  // Tier 1: text-based
  try {
    const tc = currentPdfDoc ? await _pdfPageText(currentPdfDoc, page.pageNumber) : await page.getTextContent();
    if (tc.items && tc.items.length) {
      let x1 = Infinity, y1 = Infinity, x2 = -Infinity, y2 = -Infinity;
      for (const item of tc.items) {
        if (!item.transform || !item.str || !item.str.trim()) continue;
        const tx = item.transform[4], ty = item.transform[5];
        const iw = item.width || 0, ih = item.height || Math.abs(item.transform[3]) || 0;
        for (const [px, py] of [[tx, ty], [tx + iw, ty + ih]]) {
          const [vx, vy] = natural.convertToViewportPoint(px, py);
          if (vx < x1) x1 = vx;
          if (vx > x2) x2 = vx;
          if (vy < y1) y1 = vy;
          if (vy > y2) y2 = vy;
        }
      }
      const area = (x2 - x1) * (y2 - y1);
      if (isFinite(x1) && area > pageW * pageH * 0.25) {
        return {x1: Math.max(0, x1), y1: Math.max(0, y1), x2: Math.min(pageW, x2), y2: Math.min(pageH, y2)};
      }
    }
  } catch (e) {}

  // Tier 2: pixel analysis at scale 0.3
  try {
    const lowScale = 0.3;
    const vp = page.getViewport({scale: lowScale});
    const offCanvas = document.createElement('canvas');
    offCanvas.width = Math.ceil(vp.width);
    offCanvas.height = Math.ceil(vp.height);
    const ctx = offCanvas.getContext('2d');
    await page.render({canvasContext: ctx, viewport: vp}).promise;
    const {data, width, height} = ctx.getImageData(0, 0, offCanvas.width, offCanvas.height);
    offCanvas.width = offCanvas.height = 0;

    let rMin = height, rMax = 0, cMin = width, cMax = 0;
    for (let r = 0; r < height; r++) {
      for (let c = 0; c < width; c++) {
        const idx = (r * width + c) * 4;
        if (data[idx] + data[idx + 1] + data[idx + 2] < 720) {
          if (r < rMin) rMin = r;
          if (r > rMax) rMax = r;
          if (c < cMin) cMin = c;
          if (c > cMax) cMax = c;
        }
      }
    }
    if (rMin < rMax && cMin < cMax) {
      return {x1: cMin / lowScale, y1: rMin / lowScale, x2: cMax / lowScale, y2: rMax / lowScale};
    }
  } catch (e) {}

  // Fallback: full page
  return {x1: 0, y1: 0, x2: pageW, y2: pageH};
}