doc-page.js

// @ds-adherence-ignore -- omelette starter scaffold (raw elements/hex/px by design)
// Copied omelette starter. Re-running copy_starter_component with this kind overwrites this file with the latest version (page content is unaffected).
/* BEGIN USAGE */
/**
 * <doc-page> — paged-document shell for printable HTML.
 *
 * On screen the document renders as a single continuous sheet on a desk
 * background (Google Docs' pageless view): you scroll one tall page card.
 * There is no manual page-splitting — write the whole document as normal
 * flow inside <doc-page> and the browser's print engine paginates it at
 * export.
 *
 * At print the component injects `@page { size: …; margin: 0 }` (which
 * leaves Chrome no margin box to draw its date/URL/page-count header in)
 * and moves the visual margin onto the sheet's own padding, so the printed
 * page has the same inset you see on screen. Standard break-hygiene rules
 * (`break-inside: avoid` on figures, code blocks, images and table rows;
 * `orphans/widows: 3`) are applied so paragraphs and groups split cleanly.
 * On screen and at print, headings default to `text-wrap: balance` and
 * body text (p, li, blockquote, figcaption) to `text-wrap: pretty`, so
 * the document avoids widowed/orphaned words; the defaults have zero
 * specificity, so any text-wrap you declare on those elements wins.
 * The component also marks the document as owning its print CSS (a
 * `meta[name="omelette-owns-print"]` it injects at runtime), so the
 * PDF export never injects page-geometry CSS of its own on top.
 *
 * Usage:
 *   <style>doc-page:not(:defined){visibility:hidden}</style>
 *   <doc-page size="letter" margin="0.75in">
 *     <h1>Title</h1>
 *     <p>…body…</p>
 *   </doc-page>
 *   <script src="doc-page.js"></script>
 *
 * Attributes:
 *   size    — letter | a4 | legal (default letter)
 *   orientation — portrait (default) | landscape. For documents built to
 *           export, always set it explicitly. landscape swaps the named
 *           size's dimensions (letter landscape prints 11in × 8.5in).
 *   width / height — explicit CSS lengths, override `size` and
 *           `orientation`: the page IS the design's size (a poster
 *           printed at its true dimensions). With both set, the component
 *           also declares the page box as the preview size (a
 *           `meta[name="omelette-fixed-size"]` it injects at runtime,
 *           never overriding one you author), so the in-app preview
 *           scales the whole sheet into view.
 *   content-width / content-height — the design's own fixed dimensions
 *           (CSS lengths), for scaling a fixed-size design ONTO the named
 *           paper: content lays out at exactly this size, and the
 *           component scales it to fit the printable area (centered
 *           horizontally, top-aligned), so e.g. a 960px-wide poster lands
 *           on one Letter page. Both must be set; they do not change the
 *           page box — `size`/`orientation` (or `width`/`height`)
 *           still name the paper. For pages WITHOUT running
 *           header/footer slots — the fit box fills the printable area
 *           and does not subtract slot heights.
 *   margin  — printable inset on every page (default 0.75in); margin="0"
 *           makes pages full-bleed (content then owns its own insets)
 *
 * Running header/footer (optional): give an element `slot="header"` or
 * `slot="footer"` and it repeats on every printed page via
 * `position: fixed`. To keep body text from sliding under it, the
 * component prints inside a single-cell table whose <thead>/<tfoot> are
 * spacers sized to the header/footer height — browsers repeat thead/tfoot
 * on every page, so each sheet's content starts below the header and ends
 * above the footer. On screen the header/footer render once at the
 * top/bottom of the sheet.
 *
 * Print best practices for the content you author:
 * - Multi-column text: use CSS columns (`column-count` +
 *   `column-gap`), never side-by-side flex/grid columns — only real
 *   CSS columns flow and break across pages. `column-span: all` lets
 *   a heading span the columns; `hyphens: auto` (needs `lang` on
 *   the html element) keeps narrow columns readable.
 * - Page breaks: `break-before: page` on an element that must start
 *   a new page (a chapter, an appendix). Add your own kept-together
 *   blocks (callouts, stat tiles, cards) to a `break-inside: avoid`
 *   rule, and keep each one shorter than a page.
 * - Extend `orphans: 3; widows: 3` to any custom text blocks you add
 *   (p and li are covered by default).
 * - Give long tables a <thead> — browsers repeat it on every printed
 *   page.
 * - No `position: fixed`/`sticky` and no viewport units in content:
 *   fixed elements stamp every printed page (running headers/footers go
 *   in the component's slots) and `100vh` mis-sizes at print.
 *
 * Author content as static HTML so the user can click-to-edit any text
 * directly. Do not set width/padding/background on the document body —
 * the component owns the sheet box.
 */
/* END USAGE */

(() => {
  const PAPER = {
    letter: ['8.5in', '11in'],
    a4: ['210mm', '297mm'],
    legal: ['8.5in', '14in'],
  };
  const CSS_LENGTH = /^\d+(\.\d+)?(px|in|mm|cm|pt|pc)$/;
  // Unitless "0" is a valid CSS length and the natural way to write
  // margin="0"; normalise it to 0px so max()/calc() (which reject a bare
  // number) keep working.
  const safeLen = (v, fb) => {
    v = (v || '').trim();
    return v === '0' ? '0px' : CSS_LENGTH.test(v) ? v : fb;
  };
  // CSS length → px number (CSS absolute units are exact: 1in = 96px).
  // Returns NaN for anything safeLen would reject — callers gate on it.
  const PX_PER = { px: 1, in: 96, mm: 96 / 25.4, cm: 96 / 2.54, pt: 96 / 72, pc: 16 };
  const toPx = (v) => {
    const m = /^(\d+(?:\.\d+)?)(px|in|mm|cm|pt|pc)$/.exec((v || '').trim());
    return m ? parseFloat(m[1]) * PX_PER[m[2]] : NaN;
  };

  const stylesheet = `
    :host {
      position: relative;
      display: block;
      /* When the viewport is narrower than the page, grow to wrap the
       * sheet (plus this padding) instead of staying viewport-width, so
       * the desk background and right margin reach the sheet's far edge
       * in the horizontal scroll. */
      min-width: max-content;
      min-height: 100vh;
      background: #ece8dd;
      padding: 48px 24px;
      box-sizing: border-box;
      font-family: -apple-system, BlinkMacSystemFont, "Helvetica Neue", Arial, sans-serif;
      --doc-page-w: 8.5in;
      --doc-page-h: 11in;
      --doc-page-margin: 0.75in;
      --doc-hdr-h: 0px;
      --doc-ftr-h: 0px;
      --doc-hdr-pad: 0px;
      --doc-ftr-pad: 0px;
    }
    .sheet {
      width: var(--doc-page-w);
      margin: 0 auto;
      background: #fff;
      box-shadow: 0 2px 14px rgba(20, 20, 19, 0.12);
      border-radius: 2px;
      box-sizing: border-box;
      padding: var(--doc-page-margin);
    }
    .frame { width: 100%; border-collapse: collapse; }
    /* Scaled-fit mode (content-width/content-height): the inner .fit box
     * lays the content out at its authored fixed size and scales it onto
     * the printable area; .fit-box reserves the scaled footprint in flow
     * (transforms don't affect layout) and centers it. Without the mode,
     * both divs are unstyled block pass-throughs. */
    .fit-mode .fit-box {
      width: calc(var(--doc-fit-w) * var(--doc-fit-scale));
      height: calc(var(--doc-fit-h) * var(--doc-fit-scale));
      margin: 0 auto;
      break-inside: avoid;
    }
    .fit-mode .fit {
      width: var(--doc-fit-w);
      height: var(--doc-fit-h);
      transform: scale(var(--doc-fit-scale));
      transform-origin: top left;
    }
    .frame td, .frame th { padding: 0; text-align: left; font-weight: inherit; }
    .hdr-space { height: var(--doc-hdr-h); }
    .ftr-space { height: var(--doc-ftr-h); }
    ::slotted([slot="header"]),
    ::slotted([slot="footer"]) { display: block; box-sizing: border-box; }
    @media print {
      :host { background: none; padding: 0; min-width: 0; min-height: 0; }
      .sheet {
        width: auto; margin: 0; box-shadow: none; border-radius: 0;
        padding: 0 var(--doc-page-margin);
      }
      /* The thead/tfoot spacers repeat on every page, so they carry the
       * vertical page margin (which the sheet's own padding cannot, since
       * that padding is consumed once on the first/last page). The running
       * header/footer are fixed inside that band. */
      /* The 0.35in is breathing room between a running header/footer and
       * the body; without one the spacer is exactly the page margin, so a
       * margin="0" full-bleed document gets truly full-bleed pages. */
      .hdr-space { height: max(var(--doc-page-margin), calc(var(--doc-hdr-h) + var(--doc-hdr-pad))); }
      .ftr-space { height: max(var(--doc-page-margin), calc(var(--doc-ftr-h) + var(--doc-ftr-pad))); }
      ::slotted([slot="header"]) {
        position: fixed; top: 0; left: 0; right: 0; margin: 0;
        padding: calc(var(--doc-page-margin) * 0.45) var(--doc-page-margin) 0;
      }
      ::slotted([slot="footer"]) {
        position: fixed; bottom: 0; left: 0; right: 0; margin: 0;
        padding: 0 var(--doc-page-margin) calc(var(--doc-page-margin) * 0.45);
      }
    }
  `;

  class DocPage extends HTMLElement {
    static get observedAttributes() {
      return ['size', 'width', 'height', 'margin', 'orientation', 'content-width', 'content-height'];
    }

    constructor() {
      super();
      this._root = this.attachShadow({ mode: 'open' });
      this._mo = typeof MutationObserver === 'function'
        ? new MutationObserver(() => this._scheduleMeasure())
        : null;
    }

    /** The named paper's [w, h], swapped when orientation="landscape".
     *  Only the named size swaps — explicit width/height are exact values
     *  the author already oriented. */
    _paperSize() {
      const named = PAPER[(this.getAttribute('size') || '').toLowerCase()] || PAPER.letter;
      const landscape =
        (this.getAttribute('orientation') || '').trim().toLowerCase() === 'landscape';
      return landscape ? [named[1], named[0]] : named;
    }
    get pageWidth() {
      return safeLen(this.getAttribute('width'), this._paperSize()[0]);
    }
    get pageHeight() {
      return safeLen(this.getAttribute('height'), this._paperSize()[1]);
    }
    get pageMargin() { return safeLen(this.getAttribute('margin'), '0.75in'); }

    /** Scaled-fit mode's content box [w, h] as CSS lengths, or null when
     *  the mode is off (either attribute missing/invalid/zero — a partial
     *  declaration falls back to normal flow rather than guessing). */
    _contentFit() {
      const w = safeLen(this.getAttribute('content-width'), null);
      const h = safeLen(this.getAttribute('content-height'), null);
      if (!w || !h) return null;
      const wPx = toPx(w), hPx = toPx(h);
      return wPx > 0 && hPx > 0 ? [w, h, wPx, hPx] : null;
    }

    connectedCallback() {
      if (!this._sheet) this._render();
      this._syncSize();
      this._syncPrintPageRule();
      this._ensureTextWrapDefaults();
      this._ensureOwnsPrintMeta();
      this._syncFixedSizeMeta();
      if (this._mo) this._mo.observe(this, {
        subtree: true, childList: true, characterData: true, attributes: true,
      });
      this._onResize = () => this._scheduleMeasure();
      window.addEventListener('resize', this._onResize);
      if (document.fonts && document.fonts.ready) {
        document.fonts.ready.then(() => this._scheduleMeasure());
      }
      this._scheduleMeasure();
    }

    disconnectedCallback() {
      window.removeEventListener('resize', this._onResize);
      if (this._mo) this._mo.disconnect();
      if (this._raf) { cancelAnimationFrame(this._raf); this._raf = null; }
      // Drop the head rules when the last doc-page leaves, so a deleted
      // document's @page geometry and text-wrap defaults can't apply to
      // whatever replaces it.
      const survivor = document.querySelector('doc-page');
      if (!survivor) {
        ['doc-page-print', 'doc-page-text-wrap', 'doc-page-owns-print', 'doc-page-fixed-size'].forEach((id) => {
          const tag = document.getElementById(id);
          if (tag) tag.remove();
        });
      } else if (typeof survivor._syncFixedSizeMeta === 'function') {
        // A departed true-size owner hands the page-global preview meta
        // to whatever true-size page remains (or it's removed).
        survivor._syncFixedSizeMeta();
      }
    }

    attributeChangedCallback() {
      if (!this._sheet) return;
      this._syncSize();
      this._syncPrintPageRule();
      this._syncFixedSizeMeta();
      this._scheduleMeasure();
    }

    _render() {
      this._root.innerHTML = `
        <style>${stylesheet}</style>
        <style id="vars"></style>
        <div class="sheet" data-screen-label="Document">
          <table class="frame" role="presentation">
            <thead><tr><th><div class="hdr-space"><slot name="header"></slot></div></th></tr></thead>
            <tbody><tr><td class="body"><div class="fit-box"><div class="fit"><slot></slot></div></div></td></tr></tbody>
            <tfoot><tr><td><div class="ftr-space"><slot name="footer"></slot></div></td></tr></tfoot>
          </table>
        </div>`;
      this._sheet = this._root.querySelector('.sheet');
      this._vars = this._root.getElementById('vars');
    }

    /** Runtime sizing lives in a shadow <style> :host rule, never on the
     *  light-DOM host element, so serialize-persist can't write it back. */
    _syncSize(hdrH, ftrH) {
      // Scaled-fit mode: content at its authored size, scaled onto the
      // printable area (page minus margins on both axes). The factor is a
      // plain number var so calc(length * number) stays valid; 4 decimals
      // keeps the shadow style stable across re-measures. Upscaling is
      // allowed — print transforms are vector, so text and CSS stay crisp
      // (raster images soften, which the catalog bullet warns about).
      const fit = this._contentFit();
      let fitVars = '';
      if (fit) {
        const marginPx = toPx(this.pageMargin) || 0;
        const availW = toPx(this.pageWidth) - 2 * marginPx;
        const availH = toPx(this.pageHeight) - 2 * marginPx;
        const scale = Math.min(availW / fit[2], availH / fit[3]);
        if (scale > 0 && Number.isFinite(scale)) {
          fitVars =
            '--doc-fit-w:' + fit[0] + ';' +
            '--doc-fit-h:' + fit[1] + ';' +
            '--doc-fit-scale:' + scale.toFixed(4) + ';';
        }
      }
      this._sheet.classList.toggle('fit-mode', !!fitVars);
      this._vars.textContent = ':host{' +
        fitVars +
        '--doc-page-w:' + this.pageWidth + ';' +
        '--doc-page-h:' + this.pageHeight + ';' +
        '--doc-page-margin:' + this.pageMargin + ';' +
        '--doc-hdr-h:' + (hdrH || 0) + 'px;' +
        '--doc-ftr-h:' + (ftrH || 0) + 'px;' +
        '--doc-hdr-pad:' + (hdrH ? '0.35in' : '0px') + ';' +
        '--doc-ftr-pad:' + (ftrH ? '0.35in' : '0px') + '}';
    }

    /** @page is a no-op inside shadow DOM, so the rule lives in <head>.
     *  Re-appended on every sync so it stays last in source order — the
     *  @page cascade is source-order per descriptor, so this rule wins
     *  over any other @page rule in the document. */
    _syncPrintPageRule() {
      const id = 'doc-page-print';
      let tag = document.getElementById(id);
      if (!tag) {
        tag = document.createElement('style');
        tag.id = id;
      }
      document.head.appendChild(tag);
      tag.textContent =
        '@page { size: ' + this.pageWidth + ' ' + this.pageHeight + '; margin: 0; } ' +
        '@media print { html, body { margin: 0 !important; padding: 0 !important; background: none !important; height: auto !important; overflow: visible !important; } ' +
        'h1,h2,h3,h4,h5,h6 { break-after: avoid; } ' +
        'figure,pre,blockquote,img,svg,tr { break-inside: avoid; } ' +
        'p,li { orphans: 3; widows: 3; } ' +
        '* { -webkit-print-color-adjust: exact; print-color-adjust: exact; } ' +
        '*, *::before, *::after { animation-delay: -99s !important; animation-duration: .001s !important; ' +
        'animation-iteration-count: 1 !important; animation-fill-mode: both !important; ' +
        'animation-play-state: running !important; transition-duration: 0s !important; } }';
    }

    /** Typographic defaults for document text: balance headings, avoid
     *  widowed/orphaned words in body copy (browsers without text-wrap
     *  support drop the declarations). Zero-specificity via :where() so
     *  any text-wrap authored on those elements wins; document-level so the
     *  rules reach the slotted (light DOM) content — shadow styles can't.
     *  data-omelette-injected marks the tag for the host editor to strip
     *  at serialize, so it is never written back as authored source. */
    _ensureTextWrapDefaults() {
      if (document.getElementById('doc-page-text-wrap')) return;
      const tag = document.createElement('style');
      tag.id = 'doc-page-text-wrap';
      tag.setAttribute('data-omelette-injected', '');
      tag.textContent =
        ':where(h1,h2,h3,h4,h5,h6){text-wrap:balance}' +
        ':where(p,li,blockquote,figcaption){text-wrap:pretty}';
      document.head.appendChild(tag);
    }

    /** Declares that this document owns its print CSS. The instant-PDF
     *  export checks for the meta by NAME PRESENCE alone (content is
     *  ignored) and skips its automatic print-CSS injections, so the
     *  component's @page geometry is never overridden by a heuristic.
     *  data-omelette-injected keeps it out of serialized source. */
    _ensureOwnsPrintMeta() {
      if (document.getElementById('doc-page-owns-print')) return;
      const tag = document.createElement('meta');
      tag.id = 'doc-page-owns-print';
      tag.name = 'omelette-owns-print';
      tag.content = 'true';
      tag.setAttribute('data-omelette-injected', '');
      document.head.appendChild(tag);
    }

    /** This page's valid true-size page box (explicit width AND height)
     *  as [w, h] px ints, or null when the mode is off. */
    _trueSizePx() {
      if (
        !safeLen(this.getAttribute('width'), null) ||
        !safeLen(this.getAttribute('height'), null)
      ) return null;
      const w = Math.round(toPx(this.pageWidth));
      const h = Math.round(toPx(this.pageHeight));
      return w > 0 && h > 0 ? [w, h] : null;
    }

    /** True-size pages (explicit width AND height) also declare the page
     *  box as the preview size: the in-app preview reads
     *  meta[name="omelette-fixed-size"] (content "W,H" in px ints) and
     *  scales the sheet into view — without it an 18in poster previews at
     *  true size with scrollbars. Never overrides an author-set meta
     *  (only the component's own id is managed). The meta is page-global
     *  while doc-page instances are not, so every sync recomputes the
     *  page-wide owner — the first connected true-size doc-page — and a
     *  non-true-size sibling's sync can never delete the owner's meta.
     *  Removed when no true-size page remains (the owner's disconnect
     *  re-syncs via any survivor) or when an author-set meta exists. */
    _syncFixedSizeMeta() {
      const id = 'doc-page-fixed-size';
      const own = document.getElementById(id);
      const authored = document.querySelector(
        'meta[name="omelette-fixed-size"]:not([data-omelette-injected])'
      );
      // The page-wide owner, not this instance: an upgraded true-size page
      // anywhere in the document keeps the meta alive and sized.
      let box = null;
      for (const el of document.querySelectorAll('doc-page')) {
        box = typeof el._trueSizePx === 'function' ? el._trueSizePx() : null;
        if (box) break;
      }
      if (!box || authored) {
        if (own) own.remove();
        return;
      }
      const tag = own || document.createElement('meta');
      tag.id = id;
      tag.name = 'omelette-fixed-size';
      tag.content = box[0] + ',' + box[1];
      tag.setAttribute('data-omelette-injected', '');
      if (!own) document.head.appendChild(tag);
    }

    _scheduleMeasure() {
      if (this._raf) return;
      this._raf = requestAnimationFrame(() => { this._raf = null; this._measure(); });
    }

    /** Slot heights feed the print spacers (--doc-hdr-h / --doc-ftr-h), so
     *  they re-measure on content mutation, resize, and font load. */
    _measure() {
      const hdr = this.querySelector(':scope > [slot="header"]');
      const ftr = this.querySelector(':scope > [slot="footer"]');
      this._syncSize(hdr ? hdr.offsetHeight : 0, ftr ? ftr.offsetHeight : 0);
    }
  }

  if (!customElements.get('doc-page')) {
    customElements.define('doc-page', DocPage);
  }
})();