Canviar els colors d'un document amb una sola paleta

// ═══ Postext Cookbook · Nº 054 · Retint a whole document from one palette ═══════════
// https://postext.dev/en/cookbook/live-palette-retint
// Code: MIT · Text: original (CC BY 4.0) · Artwork: design boxes generated in code (CC BY 4.0)
// Fonts: Syne, Plus Jakarta Sans (SIL OFL 1.1) · Needs postext ≥ 1.4.1
import { buildDocument, renderPageToCanvas, clearMeasurementCache, defaultResourceTypes }
  from 'https://esm.sh/postext';

const LANG = 'es'; // @lang: the language of the sample document ('en' | 'es')
const RECIPE = 'live-palette-retint';

// ─── 1 · Design ─────────────────────────────────────────────────────────────
// #region palette: three neutrals every edition shares, four entries each colourway sets
const NEUTRALS = { ink: '#1d1d1f', muted: '#5f5f66', paper: '#ffffff' };
const COLOURWAYS = { // band: colour fields · onBand: type on them · deep: accent type on paper
  red: { band: '#d7263d', onBand: '#ffffff', deep: '#b3122a', tint: '#fcdfe3' },
  teal: { band: '#2a9d8f', onBand: '#1d1d1f', deep: '#17695f', tint: '#d8eeeb' },
  violet: { band: '#6a4c93', onBand: '#ffffff', deep: '#5b3f86', tint: '#e7dff0' },
  sand: { band: '#f4a261', onBand: '#1d1d1f', deep: '#a14a16', tint: '#fde4cf' },
}; // white on teal is 3.3:1 and on sand 2.1:1, so those two set their band type in ink
const HOUSE = { ...NEUTRALS, ...COLOURWAYS.red }; // the hex config() writes beside each id
const col = (id) => ({ hex: HOUSE[id], model: 'hex', paletteId: id });
const entries = (hexes) => Object.entries(hexes).map(([id, hex]) => ({ id, name: id,
  value: { hex, model: 'hex' } })); // the shape of config.colorPalette
// #endregion

// #region answer: a colourway is a palette; retint() builds a fresh config linked to it
function retint(way) {
  const palette = { ...NEUTRALS, ...COLOURWAYS[way] };
  // 1.4.1 applies colorPalette to text, lists, boxes, chips, captions and tables, and resolves
  // swatches and cell fills against it; design elements and referenceColor print the hex
  // written beside their id, so relink() rewrites that hex (gotcha: palette-skips-designs).
  const relink = (v) => (Array.isArray(v) ? v.map(relink) : !v || typeof v !== 'object' ? v
    : Object.hasOwn(palette, v.paletteId ?? '') ? { ...v, hex: palette[v.paletteId] }
      : Object.fromEntries(Object.entries(v).map(([k, x]) => [k, relink(x)])));
  return { // a new object on every call: resolved configs are cached per object
    ...relink(config()), // (gotcha: config-cache-identity)
    colorPalette: entries({ ...palette, 'main-color': palette.band }), // the defaults take the band
  };
}
// #endregion

const [DISPLAY, SANS, BODY, LEAD] = ['Syne', 'Plus Jakarta Sans', 9.4, 13.4]; // pt: 33 lines
const [TRIM, TOP, BOTTOM, INNER, OUTER, GUTTER] = [200, 22, 22, 17, 15, 6]; // mm: square, mirrored
const BAND = 100; // mm, trim top to the colour field's foot ('bleed' is the trim: no cut lines)
const lines = (n) => pt(n * LEAD);
const caps = (size) => ({ fontFamily: SANS, fontSize: pt(size), fontWeight: 700,
  letterSpacing: pt(size * 0.16), textTransform: 'uppercase' });

// #region opener: the colour field, a waveform of palette-linked boxes, the title on top
const text = (id, content, x, y, width, style) => ({ kind: 'text', id, content, align: 'left',
  overflow: 'wrap', color: col('onBand'), placement: { anchor: { to: 'page', edge: 'top-left' },
    offset: { x: mm(x), y: mm(y) }, size: { width: mm(width) } }, ...style });
const opener = { enabled: true,
  minHeight: lines(18), // 85.1 mm: text 7 mm under the band (2.4 mm with the band box alone)
  slot: { elements: [
    { kind: 'box', id: 'band', style: { backgroundColor: col('band') },
      placement: { anchor: { to: 'bleed', edge: 'top-left' },
        size: { width: 'fill', height: mm(BAND) } } },
    ...waveform(), // boxes filled with col('tint'), which relink() rewrites like the rest
    text('kicker', '{attr.kicker}', INNER, 14, 150, caps(8)),
    text('title', '{titleText}', INNER, 20, TRIM - INNER - OUTER, { fontFamily: DISPLAY,
      fontSize: pt(46), fontWeight: 800, lineHeight: 0.92 }), // a multiple
    text('standfirst', '{attr.standfirst}', INNER, 71, 92, { fontFamily: SANS, fontSize: pt(10),
      lineHeight: 1.36 }), // (gotcha: design-lineheight-multiple)
  ] },
};
// #endregion

// #region links: every colour the engine would print in its blue, linked to a palette id
const bodyText = { fontFamily: SANS, fontSize: pt(BODY), lineHeight: pt(LEAD),
  color: col('ink'), italicColor: col('ink'), // bold: the times, key terms, boxes (inherited)
  boldColor: col('deep'), referenceColor: col('deep'), textAlign: 'left', firstLineIndent: pt(0) };
const headings = { fontFamily: DISPLAY, color: col('deep'), levels: [
  // Restated: any headings object drops the H1 break (gotcha: headings-drop-h1-break).
  { level: 1, span: 'page', breakBefore: { enabled: true, parity: 'odd' },
    marginTop: pt(0), marginBottom: pt(0), advancedDesign: opener },
  { level: 2, fontSize: pt(12.5), lineHeight: lines(1), marginTop: lines(1), marginBottom: pt(0) },
] };
const unorderedLists = { color: col('band'), indent: mm(3.6), gap: mm(1.4),
  marginTop: pt(0), marginBottom: pt(0) };
const chip = { fontSize: pt(7.5), bold: true, borderWidth: pt(0), borderRadius: mm(1.6),
  paddingX: mm(1.3), paddingY: pt(0.9), gap: mm(1) };
const chipStyles = [ // band = a ticket, tint = free: the same code as the grid overleaf
  { id: 'ticket', background: col('band'), color: col('onBand'), ...chip },
  { id: 'free', background: col('tint'), color: col('deep'), ...chip,
    borderWidth: pt(0.6), borderColor: col('band') }, // the outline keeps it off the white
];
const corner = (edge, y) => ({ anchor: { to: 'page', edge }, offset: { x: mm(OUTER), y: mm(y) } });
const furniture = (id, content, edge, y, style) => ({ elements: [{ kind: 'text', id, content,
  parity: 'even', pages: 'body', overflow: 'wrap', placement: corner(edge, y), ...style }] });
const header = furniture('head', '{title} · {subtitle}', 'top-left', 12, // page 2's head
  { ...caps(7.5), color: col('deep') });
const footer = furniture('folio', '{pageNumber}', 'bottom-left', -12, { fontFamily: SANS,
  fontSize: pt(8), fontWeight: 700, color: col('onBand'), box: { backgroundColor: col('band'),
    borderRadius: mm(2.4), padding: { top: mm(0.9), right: mm(2.4), bottom: mm(0.9),
      left: mm(2.4) } } });
// #endregion

const config = () => ({ // a factory: the engine caches resolved configs per object
  // "Tabla" in Spanish (gotcha: resource-types-locale); one table: "Table 1", not "1.1"
  resourceTypes: defaultResourceTypes(LANG).map((r) => ({ ...r, numberingTemplate: '{n}' })),
  colorPalette: entries(HOUSE), // the red edition; retint() replaces it
  page: { width: mm(TRIM), height: mm(TRIM), dpi: 150, margins: { top: mm(TOP),
    bottom: mm(BOTTOM), left: mm(INNER), right: mm(OUTER), mirror: true } },
  layout: { layoutType: 'double', gutterWidth: mm(GUTTER) },
  bodyText, headings, unorderedLists, chipStyles,
  calloutStyles: [{ id: 'tickets', backgroundEnabled: false, // no fill, a stripe on top
    stripe: { enabled: true, side: 'top', width: pt(2.5), color: col('band') },
    padding: { top: mm(2.6), right: pt(0), bottom: pt(0), left: pt(0) },
    titleStyle: { fontFamily: DISPLAY, fontSize: pt(11), color: col('deep'), gap: mm(1.2) } }],
  tableStyle: { borderColor: col('paper'), borderWidth: pt(1.6), // white rules cut the tiles
    headerBackground: col('ink'), headerColor: col('paper'), headerFontSize: pt(7.5),
    bodyFontSize: pt(8.2), bodyColor: col('ink'), cellPadding: mm(1) },
  captionStyle: { fontSize: pt(8), color: col('onBand'), labelColor: col('onBand'),
    position: 'above', backgroundEnabled: true, background: col('band'), padding: mm(1.2),
    gap: mm(1.2), note: { fontSize: pt(7.5), color: col('muted') } },
  paragraphStyles: [{ id: 'colophon', fontSize: pt(7), lineHeight: pt(9.6), color: col('muted') }],
  header, footer,
});

// ─── 2 · Content ────────────────────────────────────────────────────────────
const markdown = String.raw`---
Mostra en Markdown · 51 línies · content.es.md
title: "Música en la Ribera"
subtitle: "Programa"
author: "Sociedad Musical de Almarén"
---

# Música en \\ la Ribera {kicker="Almarén · 12–18 de junio de 2027" standfirst="Catorce citas a ambas orillas del Almar, del Escenario del Muelle a la Casa de las Barcas. Ocho son gratuitas; el resto cuesta de 9 a 14 €."}

La novena Música en la Ribera no se aleja del agua: todos los escenarios quedan a diez minutos a pie del **Escenario del Muelle**, y el **Puente de Hierro** une las dos orillas. La :ref{id="week" style="full" case="lower"} del dorso reparte la semana por escenarios y días. Los actos gratuitos no piden entrada; al Mercado de Abastos, con 300 asientos, conviene llegar pronto.

## Sábado 12 de junio

- **18.00** :chip[Gratis]{style="free"} La Banda de Música del Almar abre el pasacalles inaugural, de la escalinata del Puente de Hierro al Escenario del Muelle.
- **21.30** :chip[12 €]{style="ticket"} La Orquesta de Cámara del Almar toca la *Música acuática* de Händel desde dos barcazas amarradas frente al Muelle.

## Domingo 13 de junio

- **11.00** :chip[Gratis]{style="free"} Percusión para niños en el Mercado de Abastos: traed una cacerola y una cuchara de palo.
- **17.00** :chip[Gratis]{style="free"} El coro del Club de Remo canta habaneras en la rampa de la Casa de las Barcas.
- **20.00** :chip[14 €]{style="ticket"} El Cuarteto Ribera toca *La alondra* de Haydn y el Cuarteto en fa de Ravel en el Claustro de Santa Clara.

## Lunes 14 de junio

- **19.00** :chip[Gratis]{style="free"} Fado en el Muelle con Marta Loureiro, guitarra portuguesa y guitarra clásica.
- **22.00** :chip[9 €]{style="ticket"} El Almar Jazz Trío toca estándares y temas propios en la Casa de las Barcas.

## Martes 15 de junio

- **21.30** :chip[10 €]{style="ticket"} *Amanecer* (1927), la película muda de Murnau, en el Patio de la Curtiduría, con música nueva del Conjunto de la Curtiduría en directo. El patio abre a las 21.00.

## Miércoles 16 de junio

- **18.30** :chip[Gratis]{style="free"} Baile popular en el Muelle. Un maestro de baile enseña cada pieza antes de que arranque la banda.

## Jueves 17 de junio

- **18.00** :chip[Gratis]{style="free"} Ensayo abierto: la Orquesta de Cámara del Almar prepara *El Moldava* en el Muelle. Se escucha desde las gradas.
- **20.00** :chip[Gratis]{style="free"} Seis compositores de Almarén, una canción del río cada uno, a cargo del Coro Popular en el Mercado de Abastos.
- **22.30** :chip[9 €]{style="ticket"} Noche de cumbia en la Casa de las Barcas con Los Remeros.

## Viernes 18 de junio

- **21.00** :chip[12 €]{style="ticket"} Clausura en el Escenario del Muelle: la Orquesta de Cámara del Almar toca *El Moldava* de Smetana, que sigue un río desde sus dos fuentes hasta Praga.
- **23.45** :chip[Gratis]{style="free"} El Coro Popular canta a medianoche en la escalinata del Puente de Hierro. A las 23.15 se reparten velas.

:::callout{type="tickets" title="Entradas"}
El **abono de la semana** (48 €) da acceso a los seis conciertos con entrada. Entradas sueltas en la taquilla del Mercado desde el 7 de junio, de 10 a 14 h, o en la puerta 45 minutos antes. Los **menores de dieciséis años** entran gratis con un adulto.
:::

:::paragraphs{style="colophon"}
Organiza la Sociedad Musical de Almarén. Programa cerrado el 3 de mayo de 2027; los cambios se anuncian en la taquilla. Compuesto en Syne y Plus Jakarta Sans (SIL OFL) · Texto CC BY 4.0.
:::
`; // content.<lang>.md, inlined by the Cookbook

// #region grid: the week at a glance, filled from palette ids the engine resolves itself
const DAYS = t({ en: ['Sat 12', 'Sun 13', 'Mon 14', 'Tue 15', 'Wed 16', 'Thu 17', 'Fri 18'],
  es: ['Sáb 12', 'Dom 13', 'Lun 14', 'Mar 15', 'Mié 16', 'Jue 17', 'Vie 18'] });
const WEEK = [ // t: a ticketed concert, f: a free event, one mark a day from Saturday
  [t({ en: 'Quay Stage', es: 'Escenario del Muelle' }), 't.f.fft'],
  [t({ en: 'Iron Bridge steps', es: 'Escalinata del Puente' }), 'f.....f'],
  [t({ en: 'Market Hall', es: 'Mercado de Abastos' }), '.f...f.'],
  [t({ en: 'St Clare’s Cloister', es: 'Claustro de Santa Clara' }), '.t.....'],
  [t({ en: 'Tannery Yard', es: 'Patio de la Curtiduría' }), '...t...'],
  [t({ en: 'Boathouse', es: 'Casa de las Barcas' }), '.ft..t.'],
];
const fill = { t: col('band'), f: col('tint') }; // resources are not in the config: no relink
const resources = [{ id: 'week', typeId: 'table', kind: 'table', createdAt: 0, updatedAt: 0,
  placement: { position: 'top', span: 'page' }, // cited on page 1, it heads page 2
  caption: t({ en: 'The week at a glance', es: 'La semana de un vistazo' }),
  note: t({ en: ':swatch{color="band"} ticketed concert   :swatch{color="tint"} free event',
    es: ':swatch{color="band"} concierto con entrada   :swatch{color="tint"} acto gratuito' }),
  altText: t({ en: 'A grid of six venues by seven days; filled squares mark the events.',
    es: 'Una cuadrícula de seis escenarios por siete días; los cuadros rellenos son los actos.' }),
  table: { model: { headerRowCount: 1, columnWidths: [2.6, 1, 1, 1, 1, 1, 1, 1], rows: [
    [{ content: '', isHeader: true, background: col('paper') }, ...DAYS.map((day) => ({
      content: day, isHeader: true, align: 'center' }))],
    ...WEEK.map(([venue, marks]) => [{ content: venue, align: 'right' }, ...[...marks].map((m) =>
      (m === '.' ? { content: '' } : { content: '', background: fill[m] }))]),
  ] } } }];
// #endregion

// #region art: a waveform over the river, 29 rounded bars from a seeded generator
function waveform() {
  let seed = 0x5eed; // Mulberry32: the same bars on every run
  const random = () => {
    seed = (seed + 0x6d2b79f5) | 0;
    let x = Math.imul(seed ^ (seed >>> 15), 1 | seed);
    x = (x + Math.imul(x ^ (x >>> 7), 61 | x)) ^ x;
    return ((x ^ (x >>> 14)) >>> 0) / 4294967296;
  };
  const [x0, axis, n, width, gap] = [114, 84, 29, 2.1, 1.35]; // mm; axis: the waterline
  return Array.from({ length: n }, (_, i) => {
    const envelope = Math.sin(((i + 0.5) / n) * Math.PI) ** 0.8;
    const up = 3 + 26 * envelope * (0.35 + 0.65 * random()); // mm above the waterline
    const down = up * 0.42; // and its reflection below it
    return { kind: 'box', id: `bar-${i}`, style: { backgroundColor: col('tint'),
      borderRadius: mm(width / 2) }, placement: { anchor: { to: 'page', edge: 'top-left' },
      offset: { x: mm(x0 + i * (width + gap)), y: mm(axis - up) },
      size: { width: mm(width), height: mm(up + down) } } };
  });
}
// #endregion

// ─── 3 · Fonts ──────────────────────────────────────────────────────────────
const FONTS = { 'Plus Jakarta Sans': ['400', '400i', '700'], Syne: ['700', '800'] };

// ─── 4 · Build & show ───────────────────────────────────────────────────────
await loadFonts(FONTS, markdown);
const TITLE = t({ en: 'One programme, four palettes', es: 'Un programa, cuatro paletas' });
const build = (way) => buildWithFonts(() => buildDocument({ markdown, resources }, retint(way)),
  markdown);
const docs = {}; // red is built last: the capture shows the last build on its pages
for (const way of ['sand', 'violet', 'teal', 'red']) docs[way] = await build(way);

// #region live: four buttons, each a fresh build of the whole programme in one colourway
const NAMES = t({ en: { red: 'Red', teal: 'Teal', violet: 'Violet', sand: 'Sand' },
  es: { red: 'Rojo', teal: 'Verde azulado', violet: 'Violeta', sand: 'Arena' } });
document.getElementById('pages').insertAdjacentHTML('beforebegin', `<section id="editions">
  <div class="desk"><header><p class="kicker">${t({ en: 'Riverside Music Week · proofs',
    es: 'Música en la Ribera · pruebas' })}</p><h2>${TITLE}</h2></header><canvas id="live"
  role="img"></canvas><div class="buttons" role="group"></div></div></section>`);
const paint = (canvas, doc) => renderPageToCanvas(doc.pages[0], doc, canvas,
  { scale: (canvas.clientWidth * Math.min(devicePixelRatio, 2)) / doc.pages[0].width });
const buttons = Object.keys(COLOURWAYS).map((way) => {
  const button = document.querySelector('#editions .buttons')
    .appendChild(Object.assign(document.createElement('button'), { type: 'button' }));
  button.innerHTML = `<canvas></canvas><span>${NAMES[way]}<i>${['band', 'deep', 'tint']
    .map((id) => `<b style="background:${COLOURWAYS[way][id]}"></b>`).join('')}</i></span>`;
  paint(button.firstChild, docs[way]);
  // A fresh config on every click (retint() calls config()); the fonts are loaded by now.
  button.onclick = () => show(way, buildDocument({ markdown, resources }, retint(way)));
  return [way, button];
});
const live = document.getElementById('live');
let shown; // the document on the live page
function show(way, doc) {
  paint(live, (shown = doc));
  live.ariaLabel = `${NAMES[way]}, ${t({ en: 'page 1', es: 'página 1' })}`;
  for (const [id, button] of buttons) button.ariaPressed = String(id === way);
  showPages(doc, { title: `${TITLE} · ${NAMES[way]}` });
}
show('red', docs.red);
new ResizeObserver(() => { // canvases are bitmaps: repaint them at the desk's new size
  paint(live, shown); buttons.forEach(([way, button]) => paint(button.firstChild, docs[way]));
}).observe(live);
// #endregion

Kit · core, fonts, viewer: igual a totes les receptes · 235 línies
// ─── 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 ───────────────────────────────────────────────────────────────────────

/* The proof desk above the pages: the live page, and the four colourways as buttons.
   Sizes are in container units, so the desk keeps its 4:3 shape at any width up to 1120 px. */
#editions {
  container-type: inline-size; max-width: 1120px; margin: 0 auto; background: #16181d;
  color: #b9bcc4; font: 400 13px/1.4 "Plus Jakarta Sans", system-ui, sans-serif;
}
#editions .desk {
  box-sizing: border-box; display: grid; aspect-ratio: 4 / 3; padding: 4cqw;
  grid-template: 'page head' auto 'page ways' minmax(0, 1fr) / 67cqw minmax(0, 1fr);
  gap: 2.6cqw 3.5cqw;
}
#editions header { grid-area: head; }
#editions .kicker {
  margin: 0 0 0.8cqw; font-size: max(10px, 1cqw); font-weight: 700; letter-spacing: .18em;
  text-transform: uppercase; color: #8d9098;
}
#editions h2 { margin: 0; font: 800 2.2cqw/1.1 Syne, sans-serif; color: #f4f1ea; }
#live {
  grid-area: page; display: block; width: 67cqw; height: 67cqw; background: #fff;
  box-shadow: 0 1px 2px rgb(0 0 0 / .5), 0 2.4cqw 4.8cqw -1.8cqw rgb(0 0 0 / .85);
}
#editions .buttons {
  grid-area: ways; display: grid; grid-template-rows: repeat(4, minmax(0, 1fr)); gap: 1.3cqw;
}
#editions button {
  display: flex; align-items: center; gap: 1.6cqw; padding: 0; border: 0; background: none;
  color: #f4f1ea; font: 700 1.7cqw/1.15 Syne, sans-serif; text-align: left; cursor: pointer;
}
#editions button canvas {
  flex: none; width: 11cqw; height: 11cqw; background: #fff;
  outline: 2px solid transparent; outline-offset: 0.45cqw; transition: outline-color .15s;
}
#editions button[aria-pressed="true"] canvas { outline-color: #f4f1ea; }
#editions button:hover canvas, #editions button:focus-visible canvas { outline-color: #8d9098; }
#editions button:focus-visible { outline: none; }
#editions button i { display: flex; gap: 0.5cqw; margin-top: 0.8cqw; }
#editions button b {
  width: 1.4cqw; height: 1.4cqw; border-radius: 50%;
  box-shadow: inset 0 0 0 1px rgb(255 255 255 / .14);
}
@container (max-width: 640px) {
  #editions .desk {
    aspect-ratio: auto; padding: 24px 16px; gap: 18px;
    grid-template: 'head' auto 'page' auto 'ways' auto / minmax(0, 1fr);
  }
  #editions h2 { font-size: 24px; }
  #live { width: 100%; height: auto; aspect-ratio: 1; }
  #editions .buttons { grid-template: auto / repeat(4, minmax(0, 1fr)); gap: 10px; }
  #editions button { flex-direction: column; align-items: stretch; gap: 6px; font-size: 13px; }
  #editions button canvas { width: 100%; height: auto; aspect-ratio: 1; }
  #editions button i { gap: 4px; margin-top: 4px; }
  #editions button b { width: 10px; height: 10px; }
}