Certificate with a guilloche border

// ═══ Postext Cookbook · Nº 063 · Certificate with a guilloche border ═══════════════
// https://postext.dev/en/cookbook/certificate-single-page
// Code: MIT · Text: original (CC BY 4.0) · Guilloche and seal: generated in code (CC BY 4.0)
// Fonts: Rosarivo, Pinyon Script, Aboreto (SIL OFL 1.1) · Needs postext ≥ 1.4.1
// End-of-course certificates, one page per student, drawn by one heading style, in one PDF.
import {
  buildDocument, renderPageToCanvas, clearMeasurementCache, registerResourceImage,
} from 'https://esm.sh/postext';
import { renderToPdf, decompressWoff2 } from 'https://esm.sh/postext-pdf';

const LANG = 'en'; // @lang: the language of the sample document ('en' | 'es')
const RECIPE = 'certificate-single-page';

// ─── 1 · Design ─────────────────────────────────────────────────────────────
const palette = {
  ink: '#1f2a2e', // text and the student's name
  teal: '#1f5f5b', // the frame, the title lines
  gold: '#b08d57', // hairlines and the rule under the name; never text (2.9:1 on paper)
  seal: '#8d2c2c', // the seal and the serial number
  rule: '#8f8878', // signature lines
  muted: '#6d6a60', // the lead-in, the signatories' roles, the imprint
  paper: '#fbf8ef', // the sheet
};
const col = (id) => ({ hex: palette[id], model: 'hex', paletteId: id });
const colorPalette = Object.entries(palette)
  .map(([id, hex]) => ({ id, name: id, value: { hex, model: 'hex' } }));
const [W, H] = t({ en: [215.9, 279.4], es: [210, 297] }); // US Letter; A4 for the Spanish diploma
const MARGIN = 32; // mm on every side, inside the frame's inner rule (26 mm in)
const SIDE = 50; // mm: the certificate's side margins, a 116 mm measure (110 on A4)
// Positions are drawn on US Letter and stretched to A4: y(90) is 90 mm down on Letter.
const y = (mm) => (mm * H) / 279.4;
const SIGN = y(194); // mm from the top: the seal's top edge, where the text area ends
const SEAL = { w: 40, h: 45, r: 17 }; // mm: the seal with its ribbon tails, and its disc's radius
const at = (edge, x, top) => ({ anchor: { to: 'page', edge }, offset: { x: mm(x), y: mm(top) } });
// A tracked line is measured with a letter space after its last letter, so a centred one
// sits half a space left and a right-set one stops a space short: space() gives it in mm.
const space = (tracking) => (tracking * 25.4) / 72;
const caps = { fontFamily: 'Aboreto', textTransform: 'uppercase', color: col('teal') };

// #region answer: one heading style draws the whole certificate
const certificate = () => ({ // a function: it uses the elements defined below
  id: 'certificate',
  // Section geometry, for this style's pages only: a narrower measure, and a text area that
  // ends at the seal, so a citation too long for the page moves on instead of running under it.
  margins: { left: mm(SIDE), right: mm(SIDE), bottom: mm(H - SIGN) },
  // Header and footer elements paint over the page and reserve nothing (gotcha:
  // header-paints-over-text), so the frame, the seal and the signatures go there. In the
  // opener the signature lines would count towards its height, and a design that reaches
  // below the text area loses the whole reservation (gotcha: opener-reserves-anchored).
  header: { elements: [frame, serial] },
  footer: { elements: signatures },
  // The citation starts 18 lines of the 17 pt grid under the top margin, 140 mm down (19
  // lines, 146 mm, on A4): an opener's height rounds up to whole lines, and without
  // marginBottom: 0 the level's 0.5 em under a heading would add a line. minHeight is a
  // floor: the title block alone would start the citation at 128 mm (134 mm on A4).
  advancedDesign: { enabled: true, minHeight: mm(y(106)), slot: { elements: title } },
  marginBottom: mm(0),
});
// Hook-up: headingStyles: [certificate()], and in the Markdown one heading per student:
// # Imogen Achterberg {style="certificate" serial="26-031"}
// #endregion

// #region frame: the guilloche is an SVG resource, drawn by an image element in the header
const frame = { kind: 'image', id: 'frame', resourceId: 'guilloche',
  placement: { anchor: { to: 'page', edge: 'top-left' }, // the trim box
    size: { width: 'fill', height: 'fill' } } }; // the SVG has the page's proportions
const serial = { kind: 'text', id: 'serial', ...caps, fontSize: pt(8.5), letterSpacing: pt(1.6),
  content: t({ en: 'No. {attr.serial}', es: 'N.º {attr.serial}' }), // from the heading line
  color: col('seal'), align: 'right', placement: at('top-right', space(1.6) - MARGIN, 29) };
const PX = 10; // declared pixels per mm: an SVG resource only needs the right proportions
const svg = (id, w, h, altText) => ({ id, typeId: 'figure', kind: 'svg', createdAt: 0,
  updatedAt: 0, altText, svg: { fileId: `${id}.svg`, width: w * PX, height: h * PX } });
const resources = [
  svg('guilloche', W, H, t({ en: 'A teal guilloche border with cream rosettes at the corners.',
    es: 'Una orla de guilloché verde azulado con rosetas color crema en las esquinas.' })),
  svg('seal', SEAL.w, SEAL.h, t({ en: 'A red seal with a serrated edge and two ribbon tails.',
    es: 'Un sello rojo de borde dentado con dos cintas.' })),
];
// #endregion

// #region title: the opener holds the title block; the name is the heading's own text
const centred = (top, tracking = 0) => at('top', space(tracking) / 2, y(top));
const title = [
  { kind: 'text', id: 'kicker', ...caps, fontSize: pt(9.5), letterSpacing: pt(2.4),
    content: t({ en: 'The Quoin Room · Letterpress workshop',
      es: 'La Cuña · Taller de tipografía' }),
    placement: centred(39, 2.4) },
  { kind: 'text', id: 'title', content: t({ en: 'Certificate', es: 'Diploma' }), ...caps,
    fontSize: pt(46), lineHeight: 1, letterSpacing: pt(3), placement: centred(48, 3) },
  { kind: 'text', id: 'of', content: t({ en: 'of completion', es: 'de aprovechamiento' }),
    ...caps, fontSize: pt(11), letterSpacing: pt(4), placement: centred(68, 4) },
  { kind: 'text', id: 'lead', content: t({ en: 'This certifies that', es: 'Se otorga a' }),
    fontFamily: 'Rosarivo', italic: true, fontSize: pt(13), color: col('muted'),
    placement: centred(90) },
  { kind: 'text', id: 'name', content: '{titleText}', fontFamily: 'Pinyon Script',
    fontSize: pt(48), lineHeight: 1.25, // a multiple (gotcha: design-lineheight-multiple)
    color: col('ink'), align: 'center', overflow: 'wrap', // a long name wraps, never ends in '…'
    placement: { ...centred(97), size: { width: mm(W - 2 * MARGIN) } } },
  { kind: 'rule', id: 'underline', direction: 'horizontal', thickness: pt(0.75),
    color: col('gold'), placement: { anchor: { to: '#name', edge: 'below' },
      offset: { x: mm(18), y: mm(5) }, size: { width: mm(W - 2 * MARGIN - 36) } } },
];
// #endregion

// #region signatures: seal, signature lines, names and roles, hung from the seal's top edge
const SIGNED = t({ en: [['Harriet Colfax', 'Master printer'], ['Samuel Okoro', 'Course tutor']],
  es: [['Pilar Ansón', 'Directora del taller'], ['Julián Oteo', 'Profesor del curso']] });
// mm: each signature line stops 3 mm short of the seal (56 on Letter, 53 on A4)
const LINE = (W - 2 * MARGIN - 2 * SEAL.r) / 2 - 3;
const under = (id, gap, x = 0) => ({ anchor: { to: `#${id}`, edge: 'below' },
  offset: { x: mm(x), y: mm(gap) }, size: { width: mm(LINE) } });
const signatures = [
  { kind: 'image', id: 'seal', resourceId: 'seal',
    placement: { ...at('top', 0, SIGN), size: { width: mm(SEAL.w) } } },
  ...SIGNED.flatMap(([who, role], i) => [
    { kind: 'rule', id: `line${i}`, direction: 'horizontal', thickness: pt(0.6), color: col('rule'),
      placement: { ...at('top-left', i ? W - MARGIN - LINE : MARGIN, SIGN + 23),
        size: { width: mm(LINE) } } },
    { kind: 'text', id: `who${i}`, content: who, fontFamily: 'Rosarivo', fontSize: pt(10.5),
      color: col('ink'), align: 'center', placement: under(`line${i}`, 1.6) },
    { kind: 'text', id: `role${i}`, content: role, ...caps, fontSize: pt(7.5),
      letterSpacing: pt(1.4), color: col('muted'), align: 'center',
      placement: under(`who${i}`, 0.6, space(1.4) / 2) },
  ]),
  { kind: 'text', id: 'imprint', fontFamily: 'Rosarivo', italic: true, fontSize: pt(7),
    content: t({ en: 'Printed at the Quoin Room · set in Rosarivo, Pinyon Script and Aboreto',
      es: 'Impreso en La Cuña · compuesto en Rosarivo, Pinyon Script y Aboreto' }),
    color: col('muted'), placement: at('top', 0, SIGN + 50) },
];
// #endregion

const config = () => ({ // a factory: configs are cached by identity (gotcha: config-cache-identity)
  locale: t({ en: 'en-us', es: 'es' }), // the PDF's /Lang; centred text is never hyphenated
  colorPalette,
  page: { width: mm(W), height: mm(H), dpi: 150, backgroundColor: col('paper'),
    margins: { top: mm(MARGIN), bottom: mm(MARGIN), left: mm(MARGIN), right: mm(MARGIN) } },
  layout: { layoutType: 'single' },
  bodyText: {
    fontFamily: 'Rosarivo', fontSize: pt(11.5), lineHeight: pt(17), color: col('ink'),
    // Ink for the italic (the course title, the date line) and for any bold you add to the
    // wording; referenceColor falls back to boldColor.
    boldColor: col('ink'), italicColor: col('ink'),
    // Centred lines get no runt check (gotcha: ragged-runts): the wording was fitted by hand.
    textAlign: 'center', firstLineIndent: pt(0), paragraphSpacing: true,
  },
  // The design replaces the heading's own text, which the PDF still tags and bookmarks: set it
  // in a face the pages load, regular, since Rosarivo has no bold.
  headings: { fontFamily: 'Rosarivo', fontWeight: 400,
    // One page per student, no blank backs; the style inherits it (gotcha: headings-drop-h1-break).
    levels: [{ level: 1, breakBefore: { enabled: true, parity: 'any' } }] },
  headingStyles: [certificate()],
  header: { elements: [] }, // no page-wide furniture: the certificate style sets its own
  footer: { elements: [] },
});

// ─── 2 · Content ────────────────────────────────────────────────────────────
const markdown = String.raw`has completed *Hand Composition and Platen Printing*, a course of forty-eight hours in the fall term of 2026, and as a final piece has set by hand and printed a broadside of their own design in an edition of forty copies.
Markdown sample · 2 lines · content.en.md

*Given at Providence, Rhode Island, on December 4, 2026.*
`; // content.<lang>.md: the wording every certificate shares

// #region merge: the class list becomes one styled heading per student
// Name and serial: {titleText} and {attr.serial} in the designs (gotcha: attr-values).
const CLASS = t({
  en: [['Imogen Achterberg', '26-031'], ['Tomás Okafor', '26-032'], ['Ruth Adair', '26-033']],
  es: [['Lucía Beltrán Ochoa', '26-017'], ['Íñigo Sarasola', '26-018'], ['Ana Rius', '26-019']],
});
const merged = CLASS.map(([name, serial]) =>
  `# ${name} {style="certificate" serial="${serial}"}\n\n${markdown}`).join('\n\n');
const metadata = { // the PDF's title and author
  title: t({ en: 'Certificates of completion, fall 2026',
    es: 'Diplomas del curso de otoño de 2026' }),
  author: t({ en: 'The Quoin Room', es: 'La Cuña' }) };
// #endregion

// #region art: the guilloche frame and the seal, drawn as SVG paths
// Strokes and fills only: no <marker>, filter or mask, so the PDF keeps both drawings vector
// (gotcha: svg-no-marker-filters), and no text, which could not see the web fonts (gotcha:
// svg-no-webfonts). No random numbers, so every build draws the same curves.
const TAU = 2 * Math.PI;
const r2 = (v) => Math.round(v * 100) / 100;
// A polyline in relative moves, about a tenth smaller than in absolute coordinates.
const polyline = (pts, close = false) => `M${r2(pts[0][0])} ${r2(pts[0][1])}l${pts.slice(1)
  .map(([x, y], i) => `${r2(x - pts[i][0])} ${r2(y - pts[i][1])}`).join(' ')}${close ? 'z' : ''}`;
const gcd = (a, b) => (b ? gcd(b, a % b) : a);
// A hypotrochoid: the path of a pen at distance d from the centre of a circle of radius r
// rolling inside one of radius R, scaled to `radius` mm. It closes after r / gcd(R, r) turns.
function spiro(R, r, d, radius, steps = 1400) {
  const k = radius / (R - r + d);
  return polyline(Array.from({ length: steps + 1 }, (_, i) => {
    const a = (i / steps) * TAU * (r / gcd(R, r));
    return [((R - r) * Math.cos(a) + d * Math.cos(((R - r) / r) * a)) * k,
      ((R - r) * Math.sin(a) - d * Math.sin(((R - r) / r) * a)) * k];
  }), true);
}
// One lens of the border, `len` mm long and up to `half` mm either side of its axis: strands
// that cross at a steady rate, under an envelope that pinches them together at both ends.
const lens = (len, half, count, color) => Array.from({ length: count }, (_, k) =>
  `<path stroke="${color}" d="${polyline(Array.from({ length: 97 }, (_, i) => {
    const s = (i / 96) * len;
    const envelope = 0.56 - 0.44 * Math.cos((TAU * s) / len);
    return [s, half * envelope * Math.sin((2 * TAU * s) / len + (TAU * k) / count)];
  }))}"/>`).join('');
const BAND = [11, 23]; // the teal band, mm in from the trim; the lenses run along its middle
const MID = (BAND[0] + BAND[1]) / 2;
function guillocheSvg() {
  // Each side holds a whole number of lenses about 24 mm long: one tile per side length.
  const tiles = [['h', W - 2 * MID], ['v', H - 2 * MID]].map(([id, run]) => {
    const n = Math.round(run / 24);
    return { id, n, len: run / n, def: `<g id="${id}" stroke-width="0.2">`
      + `${lens(run / n, 5.4, 11, palette.paper)}${lens(run / n, 2.6, 3, palette.gold)}</g>` };
  });
  const use = (id, x, y, turn) => `<use href="#${id}" transform="translate(${r2(x)} ${r2(y)})`
    + ` rotate(${turn})"/>`;
  const uses = tiles.flatMap(({ id, n, len }) => Array.from({ length: n }, (_, i) => MID + i * len)
    .flatMap((p) => (id === 'h' ? [use(id, p, MID, 0), use(id, p, H - MID, 0)]
      : [use(id, MID, p, 90), use(id, W - MID, p, 90)])));
  const ring = (inset, color, width) => `<rect x="${inset}" y="${inset}"`
    + ` width="${r2(W - 2 * inset)}" height="${r2(H - 2 * inset)}" stroke="${color}"`
    + ` stroke-width="${width}"/>`;
  const box = (inset) => `M${inset} ${inset}h${r2(W - 2 * inset)}v${r2(H - 2 * inset)}`
    + `h${r2(2 * inset - W)}z`;
  // A cream medallion on the teal band, so each corner reads as a disc at thumbnail size.
  const rosette = `<g id="rosette"><circle r="10" fill="${palette.paper}" stroke="${palette.gold}"`
    + ` stroke-width="0.6"/><circle r="9.1" stroke="${palette.teal}" stroke-width="0.25"/>`
    + `<path d="${spiro(30, 13, 9, 8.2)}" stroke="${palette.teal}" stroke-width="0.16"/>`
    + `<circle r="1.4" fill="${palette.gold}"/></g>`;
  const corners = [[MID, MID], [W - MID, MID], [MID, H - MID], [W - MID, H - MID]]
    .map(([x, y]) => use('rosette', x, y, 0));
  return `<svg xmlns="http://www.w3.org/2000/svg" width="${r2(W * PX)}" height="${r2(H * PX)}"`
    + ` viewBox="0 0 ${W} ${H}"><defs>${tiles.map((tile) => tile.def).join('')}${rosette}</defs>`
    + `<g fill="none" stroke-linecap="round" stroke-linejoin="round">${ring(9, palette.gold, 0.35)}`
    + `<path fill="${palette.teal}" fill-rule="evenodd" d="${box(BAND[0])}${box(BAND[1])}"/>`
    + `${uses.join('')}${ring(25, palette.gold, 0.6)}${ring(26.2, palette.teal, 0.2)}`
    + `${corners.join('')}</g></svg>`;
}
function sealSvg() {
  const [cx, cy, R] = [SEAL.w / 2, 19, SEAL.r];
  const teeth = Array.from({ length: 144 }, (_, i) => [
    cx + (i % 2 ? R : R - 1.3) * Math.cos((i / 144) * TAU),
    cy + (i % 2 ? R : R - 1.3) * Math.sin((i / 144) * TAU)]);
  // Two ribbon tails behind the seal, notched at the ends; the far one a shade darker.
  const tail = (s) => polyline([[cx + s * 3, cy], [cx + s * 12, cy + 24], [cx + s * 9, cy + 21.6],
    [cx + s * 6, cy + 25.5], [cx - s * 3, cy + 3]], true);
  return `<svg xmlns="http://www.w3.org/2000/svg" width="${SEAL.w * PX}" height="${SEAL.h * PX}"`
    + ` viewBox="0 0 ${SEAL.w} ${SEAL.h}"><path d="${tail(-1)}" fill="#6f2323"/>`
    + `<path d="${tail(1)}" fill="${palette.seal}"/>`
    + `<path d="${polyline(teeth, true)}" fill="${palette.seal}"/>`
    + `<g fill="none" stroke="${palette.paper}" stroke-linecap="round">`
    + `<circle cx="${cx}" cy="${cy}" r="${R - 3}" stroke-width="0.35"/>`
    + `<circle cx="${cx}" cy="${cy}" r="${R - 3.8}" stroke-width="0.15"/>`
    + `<path transform="translate(${cx} ${cy})" d="${spiro(24, 11, 9, R - 5)}"`
    + ' stroke-width="0.14"/>'
    + `</g><circle cx="${cx}" cy="${cy}" r="1.3" fill="${palette.paper}"/></svg>`;
}
// #endregion

// ─── 3 · Fonts ──────────────────────────────────────────────────────────────
// Loaded from Fontsource before the first build: layout measures with them (gotcha: fonts-first)
const FONTS = { Rosarivo: ['400', '400i'], 'Pinyon Script': ['400'], Aboreto: ['400'] };

// ─── 4 · Build & show ───────────────────────────────────────────────────────
await loadFonts(FONTS, merged);
await loadSvg('guilloche.svg', guillocheSvg());
await loadSvg('seal.svg', sealSvg());
const doc = await buildWithFonts(() => buildDocument({ markdown: merged, metadata, resources },
  config()), merged);
showPages(doc, { title: t({ en: 'Certificate with a guilloche border',
  es: 'Diploma con orla de guilloché' }) });
// #region pdf: one document with a page per student, so one PDF holds the whole class
// The PDF also asks for bold and bold italic Rosarivo, which the family does not ship: the
// kit's provider snaps each request to the nearest face (gotcha: pdf-provider-all-styles).
offerPdf(() => renderToPdf(doc, { fontProvider: fontsourceProvider, resourceBytes: imageBytes }),
  `${RECIPE}.pdf`); // bookmarks: one per heading, so one per student
document.querySelector('[data-postext-pdf]').textContent = t({ en: 'Class list → one PDF',
  es: 'Toda la clase en un PDF' });
// #endregion

Kit · core, fonts, viewer, pdf, images: the same in every recipe · 310 lines
// ─── Kit ── helpers shared by every Cookbook recipe · postext.dev/cookbook ─────

// ─── Kit · core v1 ── the same in every recipe · postext.dev/cookbook ─────────
function mm(value) { return { value, unit: 'mm' }; }
function pt(value) { return { value, unit: 'pt' }; }
function em(value) { return { value, unit: 'em' }; }
/** The sample language's string: t({ en: 'Figure', es: 'Figura' }). */
function t(strings) { return strings[LANG] ?? Object.values(strings)[0]; }
/** A file in this recipe's assets folder, served from the Postext repo by jsDelivr. */
function asset(file) { return `https://cdn.jsdelivr.net/gh/drnachio/postext@main/cookbook/${RECIPE}/assets/${file}`; }

// ─── Kit · fonts v1 ── the same in every recipe · postext.dev/cookbook ────────
// Postext measures text with the faces the browser has loaded, and caches the
// widths, so every face must be ready before the first build. Faces come from
// Fontsource: the same static files the PDF embeds, so screen and PDF agree.

/** faces = { 'Family Name': ['400', '400i', '700'] }. `text` is the sample:
 *  letters beyond Latin-1 (č, ł, ő…) also load the latin-ext files. With
 *  `optional`, a face Fontsource does not ship is skipped instead of failing.
 *  Resolves to the number of faces added. */
async function loadFonts(faces, text = '', { optional = false } = {}) {
  kitStatus('Loading fonts…');
  const ranges = {
    latin: 'U+0000-00FF,U+0131,U+0152-0153,U+02BB-02BC,U+02C6,U+02DA,U+02DC,U+0304,U+0308,U+0329,'
      + 'U+2000-206F,U+20AC,U+2122,U+2191,U+2193,U+2212,U+2215,U+FEFF,U+FFFD',
    'latin-ext': 'U+0100-02BA,U+02BD-02C5,U+02C7-02CC,U+02CE-02D7,U+02DD-02FF,U+0304,U+0308,U+0329,'
      + 'U+1D00-1DBF,U+1E00-1E9F,U+1EF2-1EFF,U+2020,U+20A0-20AB,U+20AD-20C0,U+2113,U+2C60-2C7F,U+A720-A7FF',
  };
  const subsets = /[Ā-˿Ḁ-ỿ]/.test(text) ? ['latin', 'latin-ext'] : ['latin'];
  const jobs = [];
  let added = 0;
  for (const [family, specs] of Object.entries(faces)) {
    const id = fontsourceId(family);
    const meta = optional ? await fontsourceMeta(family) : null;
    for (const spec of new Set(specs)) {
      const weight = parseInt(spec, 10);
      const style = spec.endsWith('i') ? 'italic' : 'normal';
      if (hasFace(family, weight, style)) continue;
      if (optional && !(meta?.weights.includes(weight) && meta.styles.includes(style))) continue;
      for (const subset of subsets) {
        const url = `https://cdn.jsdelivr.net/npm/@fontsource/${id}@5/files/${id}-${subset}-${weight}-${style}.woff2`;
        const face = new FontFace(family, `url(${url}) format('woff2')`,
          { weight: String(weight), style, unicodeRange: ranges[subset] });
        jobs.push(face.load().then((ready) => { document.fonts.add(ready); added++; }, () => {
          if (subset === 'latin' && !optional) throw new Error(`Fontsource has no ${family} ${weight} ${style}`);
        }));
      }
    }
  }
  await Promise.all(jobs).catch((error) => { kitFail(error); throw error; });
  return added;
}

/** Runs `build` (a buildDocument or buildBundle call) and checks the faces
 *  the pages use. A regular face missing from FONTS is loaded with a warning;
 *  bold and italic variants are loaded when the family ships them. Then the
 *  measurement caches are cleared and the build runs again. */
async function buildWithFonts(build, text = '') {
  const tried = new Set();
  for (let round = 0; round < 3; round++) {
    kitStatus('Laying out…');
    await new Promise(requestAnimationFrame);          // let the status paint first
    const result = await Promise.resolve().then(build).catch((error) => { kitFail(error); throw error; });
    const wanted = { base: {}, variants: {} };
    for (const { font, base } of [result].flat().flatMap(fontStringsOf)) {
      const { family, weight, style } = parseFont(font);
      const key = `${family}|${weight}|${style}`;
      if (tried.has(key) || hasFace(family, weight, style)) continue;
      tried.add(key);
      (wanted[base ? 'base' : 'variants'][family] ??= []).push(`${weight}${style === 'italic' ? 'i' : ''}`);
    }
    if (Object.keys(wanted.base).length) {
      console.warn(`[cookbook] FONTS does not list ${JSON.stringify(wanted.base)}: loading them.`);
    }
    const added = await loadFonts(wanted.base, text) + await loadFonts(wanted.variants, text, { optional: true });
    if (added === 0) return result;
    clearMeasurementCache();
  }
  throw new Error('The fonts did not settle after three builds.');
}

/** Every font string of the layout. `base` marks a block's own face; its
 *  bold, italic and bold-italic variants are listed whether or not used. */
function fontStringsOf(doc) {
  const found = new Map();
  const walk = (node) => {
    if (!node || typeof node !== 'object') return;
    if (Array.isArray(node)) { node.forEach(walk); return; }
    for (const [key, value] of Object.entries(node)) {
      if (typeof value === 'string' && /fontString$/i.test(key)) {
        found.set(value, found.get(value) || key === 'fontString');
      } else if (value && typeof value === 'object') walk(value);
    }
  };
  walk(doc.pages);
  walk(doc.blocks);
  return [...found].map(([font, base]) => ({ font, base }));
}

/** '700 37.5px Open Sans' / 'italic 400 13px "Source Serif 4"' → { family, weight, style }.
 *  A string with no weight ('95.8px Young Serif', from a design text) is 400. */
function parseFont(font) {
  const m = /^(?:(italic|oblique)\s+)?(?:small-caps\s+)?(?:(\d+|bold|normal)\s+)?[\d.]+px\s+(.+)$/.exec(font.trim());
  if (!m) throw new Error(`Unexpected font string: ${font}`);
  const weight = m[2] === 'bold' ? 700 : !m[2] || m[2] === 'normal' ? 400 : Number(m[2]);
  return { family: m[3].replace(/^["']|["']$/g, ''), weight, style: m[1] ? 'italic' : 'normal' };
}

/** True when a loaded FontFace covers exactly this family, weight and style
 *  (document.fonts.check() is also true for families nobody declared). */
function hasFace(family, weight, style) {
  for (const face of document.fonts) {
    if (face.status !== 'loaded' || face.style !== style) continue;
    if (face.family.replace(/^["']|["']$/g, '') !== family) continue;
    const [low, high = low] = face.weight.split(' ').map(Number);
    if (weight >= low && weight <= high) return true;
  }
  return false;
}

/** Fontsource's id for a family: 'Source Serif 4' → 'source-serif-4'. */
function fontsourceId(family) { return family.toLowerCase().replace(/\s+/g, '-'); }

/** The weights and styles a family ships ({ weights: [400, 700], styles: ['normal', 'italic'] }), or null. */
function fontsourceMeta(family) {
  fontsourceMeta.cache ??= new Map();
  const id = fontsourceId(family);
  if (!fontsourceMeta.cache.has(id)) {
    fontsourceMeta.cache.set(id, fetch(`https://api.fontsource.org/v1/fonts/${id}`)
      .then((res) => (res.ok ? res.json() : null), () => null));
  }
  return fontsourceMeta.cache.get(id);
}

// ─── Kit · viewer v1 ── the same in every recipe · postext.dev/cookbook ───────
/** Shows the pages as facing spreads on a dark desk: the first page is a
 *  recto on its own, then verso | recto pairs, as in a bound book. Pages
 *  are painted when they scroll near the screen. */
function showPages(docs, { title, width = 460 } = {}) {
  const root = viewer(title);
  const pages = [docs].flat().flatMap((doc) =>
    doc.pages.map((page) => ({ doc, page, n: (doc.pageIndexOffset ?? 0) + page.index })));
  const spreads = [];
  let verso = null;
  for (const p of pages) {
    if (p.n % 2 === 1) { if (verso) spreads.push([verso, null]); verso = p; }
    else { spreads.push([verso, p]); verso = null; }
  }
  if (verso) spreads.push([verso, null]);
  const density = Math.min(window.devicePixelRatio || 1, 2);
  showPages.painter?.disconnect();
  const painter = new IntersectionObserver((entries) => {
    for (const { isIntersecting, target } of entries) {
      if (!isIntersecting) continue;
      painter.unobserve(target);
      const { doc, page } = target.postext;
      renderPageToCanvas(page, doc, target, { scale: (width * density) / page.width });
    }
  }, { rootMargin: '800px' });
  showPages.painter = painter;
  root.replaceChildren(...spreads.map((pair) => {
    const spread = document.createElement('div');
    spread.className = 'pt-spread';
    for (const p of pair) {
      const figure = document.createElement('figure');
      if (p) {
        const label = p.page.pageLabel || String(p.n + 1);
        const canvas = document.createElement('canvas');
        canvas.postext = p;
        canvas.style.aspectRatio = `${p.page.width} / ${p.page.height}`;
        canvas.setAttribute('role', 'img');
        canvas.setAttribute('aria-label', `Page ${label}`);
        const folio = document.createElement('figcaption');
        folio.textContent = label;
        figure.append(canvas, folio);
        painter.observe(canvas);
      } else figure.className = 'pt-blank';
      spread.append(figure);
    }
    return spread;
  }));
  kitStatus(`${pages.length} ${pages.length === 1 ? 'page' : 'pages'}`);
  document.documentElement.dataset.postext = 'ready';
  return pages.length;
}

/** The desk, the bar and the error reporting, created once. */
function viewer(title) {
  if (!document.getElementById('pt-kit')) {
    document.head.insertAdjacentHTML('beforeend', `<style id="pt-kit">
      :root { color-scheme: dark; }
      body { margin: 0; background: #0e1014; color: #b9bcc4; font: 13px/1.45 system-ui, sans-serif; }
      #pt-bar { position: sticky; top: 0; z-index: 1; display: flex; flex-wrap: wrap; align-items: center;
        gap: 6px 16px; padding: 10px 16px; background: rgb(14 16 20 / .92); backdrop-filter: blur(6px);
        border-bottom: 1px solid #23262d; }
      #pt-bar strong { color: #f4f1ea; font-weight: 600; }
      #pt-actions { display: flex; gap: 12px; margin-left: auto; }
      #pt-actions a, #pt-actions button { color: #d8a21a; font: inherit; background: none; border: 0; padding: 0; cursor: pointer; }
      #pages { display: grid; justify-items: center; gap: 48px; padding: 32px 16px 72px; }
      .pt-spread { display: flex; }
      .pt-spread figure { margin: 0; width: min(460px, 44vw); }
      .pt-spread canvas { display: block; width: 100%; background: #fff;
        box-shadow: 0 1px 2px rgb(0 0 0 / .5), 0 22px 44px -16px rgb(0 0 0 / .8); }
      .pt-spread figure:first-child canvas { box-shadow: inset -14px 0 14px -14px rgb(0 0 0 / .18), 0 1px 2px rgb(0 0 0 / .5), 0 22px 44px -16px rgb(0 0 0 / .8); }
      .pt-spread figcaption { margin-top: 10px; text-align: center; font: 600 10px/1 system-ui, sans-serif;
        letter-spacing: .18em; text-transform: uppercase; color: #6c7079; }
      .pt-blank { visibility: hidden; }
      @media (max-width: 760px) {
        .pt-spread { flex-direction: column; gap: 32px; }
        .pt-spread figure { width: min(460px, 92vw); }
        .pt-blank { display: none; }
      }
    </style>`);
    document.body.insertAdjacentHTML('afterbegin',
      '<header id="pt-bar"><strong id="pt-title"></strong><span id="pt-status" role="status"></span><span id="pt-actions"></span></header>');
    document.getElementById('pt-title').textContent = document.title || 'Postext';
    addEventListener('error', (event) => kitFail(event.error ?? event.message));
    addEventListener('unhandledrejection', (event) => kitFail(event.reason));
  }
  if (title) document.getElementById('pt-title').textContent = title;
  return document.getElementById('pages')
    ?? document.body.appendChild(Object.assign(document.createElement('main'), { id: 'pages' }));
}

function kitStatus(text) {
  viewer();
  document.getElementById('pt-status').textContent = text;
}

function kitFail(error) {
  document.documentElement.dataset.postext = 'error';
  kitStatus(`Error: ${error?.message ?? error}`);
}

// ─── Kit · pdf v1 ── the same in every recipe that exports a PDF ──────────────
/** postext-pdf embeds TrueType bytes. Fetch the Fontsource file the screen
 *  used, snapping to a weight the family ships and falling back to upright
 *  when it has no italic: the PDF asks for every face a block could use. */
async function fontsourceProvider(family, weight, style) {
  const id = fontsourceId(family);
  const meta = await fontsourceMeta(family);
  const weights = meta?.weights?.length ? meta.weights : [400, 700];
  const w = weights.reduce((a, b) => (Math.abs(b - weight) < Math.abs(a - weight) ? b : a));
  const s = style === 'italic' && meta && !meta.styles.includes('italic') ? 'normal' : style;
  const res = await fetch(`https://cdn.jsdelivr.net/npm/@fontsource/${id}@5/files/${id}-latin-${w}-${s}.woff2`);
  if (!res.ok) throw new Error(`Fontsource has no ${family} ${w} ${s} (${res.status})`);
  return decompressWoff2(new Uint8Array(await res.arrayBuffer()));
}

/** A "Build the PDF" button in the bar. Once built: "Open the PDF" (a new
 *  tab, since CodePen's preview frame cannot show PDFs) and a download link. */
function offerPdf(makePdf, filename) {
  viewer();
  const button = Object.assign(document.createElement('button'), { type: 'button', textContent: 'Build the PDF' });
  button.dataset.postextPdf = filename;
  button.addEventListener('click', async () => {
    button.disabled = true;
    button.textContent = 'Building the PDF…';
    try {
      const bytes = await makePdf();
      const url = URL.createObjectURL(new Blob([bytes], { type: 'application/pdf' }));
      const size = `${Math.max(1, Math.round(bytes.length / 1024))} KB`;
      button.replaceWith(
        Object.assign(document.createElement('a'), { href: url, target: '_blank', rel: 'noopener', textContent: 'Open the PDF ↗' }),
        Object.assign(document.createElement('a'), { href: url, download: filename, textContent: `Download ${filename} · ${size}` }));
    } catch (error) {
      button.disabled = false;
      button.textContent = 'Build the PDF';
      kitFail(error);
    }
  });
  document.getElementById('pt-actions').append(button);
}

// ─── Kit · images v1 ── recipes with pictures · postext.dev/cookbook ──────────
/** Registers a photo or PNG for the canvas and keeps its bytes for the PDF.
 *  fetch → ImageBitmap never taints the canvas (a plain cross-origin <img> would). */
async function loadImage(fileId, url) {
  const res = await fetch(url);
  if (!res.ok) throw new Error(`Image not found (${res.status}): ${url}`);
  const bytes = new Uint8Array(await res.arrayBuffer());
  registerResourceImage(fileId, await createImageBitmap(new Blob([bytes])));
  (loadImage.bytes ??= new Map()).set(fileId, bytes);
}

/** Registers SVG markup (drawn in code, or fetched) as a vector image. */
async function loadSvg(fileId, svg) {
  const img = new Image();
  img.src = `data:image/svg+xml;charset=utf-8,${encodeURIComponent(svg)}`;
  await img.decode();
  registerResourceImage(fileId, img);
  (loadImage.bytes ??= new Map()).set(fileId, new TextEncoder().encode(svg));
}

/** renderToPdf({ resourceBytes: imageBytes }) */
function imageBytes(fileId) { return loadImage.bytes?.get(fileId); }

/** renderToHtml({ resourceImageUrl: imageUrl }) */
function imageUrl(fileId) {
  const bytes = imageBytes(fileId);
  if (!bytes) return undefined;
  imageUrl.urls ??= new Map();
  if (!imageUrl.urls.has(fileId)) {
    const type = /\.svg$/i.test(fileId) ? 'image/svg+xml' : /\.png$/i.test(fileId) ? 'image/png' : 'image/jpeg';
    imageUrl.urls.set(fileId, URL.createObjectURL(new Blob([bytes], { type })));
  }
  return imageUrl.urls.get(fileId);
}

// ─── /Kit ───────────────────────────────────────────────────────────────────────