A qasida on a diwan page, each line in two hemistichs

// ═══ Postext Cookbook · Nº 110 · A qasida on a diwan page, in two hemistichs ═══════════
// https://postext.dev/en/cookbook/qasida-diwan-page
// Code: MIT · Text: al-Mutanabbī, Dīwān, ar.wikisource (PD) · Pictures: none
// Fonts: Amiri, Aref Ruqaa, Noto Kufi Arabic (SIL OFL 1.1) · Needs postext ≥ 1.15.0
import { buildDocument, renderPageToCanvas, clearMeasurementCache } 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 = 'qasida-diwan-page';

// ─── 1 · Design ─────────────────────────────────────────────────────────────
// Black text and red rubrics on a warm paper, as a Cairo diwan of the 1900s prints them.
const palette = {
  ink: '#1f1a16', // text: a warm near-black
  rubric: '#9a2b1f', // the accent: titles, the metre, the headpiece rules
  tint: '#f1e6cf', // the headpiece band
  rule: '#b8a27c', // hairlines
  muted: '#6b6156', // running heads and the note on the text
  paper: '#fbf7ee', // a cream paper
};
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' } })),
  { id: 'main-color', name: 'rubric (defaults)', value: { hex: palette.rubric, model: 'hex' } },
];
const NASKH = 'Amiri'; // the text: a Bulaq Naskh
const RUQAA = 'Aref Ruqaa'; // display: the titles
const KUFI = 'Noto Kufi Arabic'; // labels: metre, running heads, folios
const [SIZE, LEAD] = [13, 21]; // pt: the prose, at 1.6 × for a lightly vocalised headnote
const [OUTER, TOP] = [18, 23]; // mm: a 17 × 24 cm diwan

// #region answer: one bayt a line, both hemistichs stretched to one width
// In the Markdown, a :::verse block takes one bayt a line, the ṣadr and the ʿajuz parted
// by ||:
//   :::verse{style="bayt"}
//   عَلى قَدْرِ أهْلِ العَزْم تأتي العَزائِمُ || وَتأتي علَى قَدْرِ الكِرامِ المَكارمُ
//   :::
// The ṣadr goes on the right, the ʿajuz on the left, both stretched to the width of the
// widest half with a gap of 2 em between them. The style gives the poem its face and a
// leading deep enough for the harakat: 1.9 × the size.
const bayt = { id: 'bayt', fontFamily: NASKH, fontSize: pt(14), lineHeight: pt(26.6),
  color: col('ink'), marginTop: pt(LEAD / 2), marginBottom: pt(LEAD) };
// Justified lines lengthen their words with kashidas (tatweel) before they open the
// spaces wide: 'auto' is the default in an Arabic document, written out here to say so.
// A hemistich may stretch a word twice as far as a line of prose does: 1.2 em.
const bodyKashida = { kashida: 'auto', kashidaPatterns: 'naskh', kashidaMaxLength: 0.6 };
// #endregion

// #region opener: a headpiece band with the title in Ruqʿa and the metre under it
const rule = (id, y, thickness) => ({ kind: 'rule', id, direction: 'horizontal',
  thickness: pt(thickness), color: col('rubric'),
  placement: { anchor: { to: 'container', edge: 'top' }, offset: { y: mm(y) },
    size: { width: 'fill' } } });
const opener = {
  enabled: true, minHeight: mm(46),
  slot: { elements: [
    { kind: 'box', id: 'band', reserve: false, style: { backgroundColor: col('tint') },
      placement: { anchor: { to: 'container', edge: 'top' }, offset: { y: mm(4) },
        size: { width: 'fill', height: mm(26) } } },
    rule('band-top', 4, 1.5), rule('band-foot', 30, 0.5),
    { kind: 'text', id: 'title', content: '{titleText}', fontFamily: RUQAA, fontWeight: 700,
      fontSize: pt(34), lineHeight: 1.1, align: 'center', color: col('rubric'),
      placement: { anchor: { to: 'container', edge: 'top' }, offset: { y: mm(7.5) } } },
    { kind: 'text', id: 'metre', content: '{attr.metre}', fontFamily: KUFI, fontWeight: 500,
      fontSize: pt(9), align: 'center', color: col('muted'),
      placement: { anchor: { to: 'container', edge: 'top' }, offset: { y: mm(35) } } },
  ] },
};
// #endregion

// #region title: the diwan's half-title, centred on the page
const at = (y) => ({ anchor: { to: 'page', edge: 'top' }, offset: { y: mm(y) } });
const line = (id, content, y, style) => ({ kind: 'text', id, content, align: 'center',
  overflow: 'wrap', color: col('ink'), placement: at(y), ...style });
const titlePage = {
  id: 'title', span: 'page', runningChapter: false,
  breakBefore: { enabled: true, parity: 'any' },
  header: { elements: [] }, footer: { elements: [] },
  advancedDesign: { enabled: true, slot: { elements: [
    line('diwan', 'ديوان', 52, { fontFamily: RUQAA, fontWeight: 700, fontSize: pt(64),
      lineHeight: 1.2, color: col('rubric') }),
    line('poet', '{titleText}', 84, { fontFamily: NASKH, fontWeight: 700, fontSize: pt(20) }),
    { kind: 'rule', id: 'rule', direction: 'horizontal', thickness: pt(0.75),
      color: col('rubric'), placement: { anchor: { to: 'page', edge: 'top' },
        offset: { y: mm(100) }, size: { width: mm(24) } } },
    line('rhyme', '{attr.rhyme}', 106, { fontFamily: KUFI, fontWeight: 500, fontSize: pt(11),
      color: col('rubric') }),
    line('latin', '{attr.latin}', 150, { fontFamily: NASKH, fontSize: pt(9.5),
      color: col('muted'), italic: true }),
  ] } },
};
// #endregion

// #region heads: the book on the verso, the rhyme on the recto, folios outside
// Running heads stay on the sheet's sides: in a book bound on the right the verso (even)
// is the right-hand page, so its outer edge, where the folio goes, is the right one.
const head = (id, content, parity, edge, x, extra = {}) => ({ kind: 'text', id, content,
  parity, pages: 'body', fontFamily: KUFI, fontWeight: 500, fontSize: pt(8.5),
  color: col('muted'), placement: { anchor: { to: 'page', edge }, offset: { x: mm(x), y: mm(12) } },
  ...extra });
const header = { elements: [
  head('verso-folio', '{pageNumber}', 'even', 'top-right', -OUTER, { color: col('ink') }),
  head('verso-book', '{title}', 'even', 'top-right', -(OUTER + 10)),
  head('recto-rhyme', '{subtitle}', 'odd', 'top-left', OUTER + 10),
  head('recto-folio', '{pageNumber}', 'odd', 'top-left', OUTER, { color: col('ink') }),
] };
const footer = { elements: [head('drop-folio', '{pageNumber}', 'all', 'bottom', 0, {
  pages: 'opener', color: col('ink'),
  placement: { anchor: { to: 'page', edge: 'bottom' }, offset: { y: mm(-12) } } })] };
// #endregion

const config = () => ({ // a factory: the engine caches resolved configs per object
  locale: 'ar', // right to left, bound on the right, digits ٠–٩ (gotcha: arabic-locale-tag)
  colorPalette,
  page: { width: mm(170), height: mm(240), dpi: 150, backgroundColor: col('paper'),
    margins: { top: mm(TOP), bottom: mm(22), left: mm(21), right: mm(OUTER), mirror: true } },
  layout: { layoutType: 'single' },
  bodyText: { fontFamily: NASKH, fontSize: pt(SIZE), lineHeight: pt(LEAD), color: col('ink'),
    boldColor: col('ink'), italicColor: col('ink'), referenceColor: col('ink'),
    textAlign: 'justify', firstLineIndent: em(1.5), indentAfterHeading: false,
    optimalLineBreaking: true, avoidWidows: true, avoidOrphans: true, ...bodyKashida },
  // Restated: any headings object drops the H1 break (gotcha: headings-drop-h1-break).
  headings: { fontFamily: RUQAA, fontWeight: 700, color: col('rubric'),
    levels: [{ level: 1, fontSize: pt(34), breakBefore: { enabled: true, parity: 'any' },
      advancedDesign: opener }] },
  headingStyles: [titlePage],
  paragraphStyles: [bayt,
    { id: 'note', fontFamily: NASKH, fontSize: pt(9.5), lineHeight: pt(14), color: col('muted'),
      boldColor: col('ink'), italicColor: col('muted'), textAlign: 'justify',
      firstLineIndent: pt(0), marginTop: pt(LEAD), hyphenation: { enabled: true, locale: LANG } },
    { id: 'colophon', fontFamily: NASKH, fontSize: pt(8), lineHeight: pt(11),
      color: col('muted'), textAlign: 'left', firstLineIndent: pt(0), marginTop: pt(7) },
  ],
  header, footer,
});

// ─── 2 · Content ────────────────────────────────────────────────────────────
const markdown = String.raw`---
Markdown sample · 66 lines · content.en.md
title: "ديوان المتنبي"
subtitle: "قافية الميم"
---

# أبي الطيّب المتنبّي {style="title" rhyme="قافية الميم" latin="The Dīwān of al-Mutanabbī · poems rhyming in mīm"}

# على قدر أهل العزم {metre="من البحر الطويل"}

وقال يمدح سيفَ الدولة ويذكر بناءه قلعةَ الحَدَث الحمراء على ثغر الروم، وقد هزم الدُّمُسْتُق تحت أسوارها، سنة ثلاث وأربعين وثلاثمئة:

:::verse{style="bayt"}
عَلى قَدْرِ أهْلِ العَزْم تأتي العَزائِمُ || وَتأتي علَى قَدْرِ الكِرامِ المَكارمُ
وَتَعْظُمُ في عَينِ الصّغيرِ صغارُها || وَتَصْغُرُ في عَين العَظيمِ العَظائِمُ
يُكَلّفُ سيفُ الدّوْلَةِ الجيشَ هَمّهُ || وَقد عَجِزَتْ عنهُ الجيوشُ الخضارمُ
وَيَطلُبُ عندَ النّاسِ ما عندَ نفسِه || وَذلكَ ما لا تَدّعيهِ الضّرَاغِمُ
يُفَدّي أتَمُّ الطّيرِ عُمْراً سِلاحَهُ || نُسُورُ الفَلا أحداثُها وَالقَشاعِمُ
وَما ضَرّها خَلْقٌ بغَيرِ مَخالِبٍ || وَقَدْ خُلِقَتْ أسيافُهُ وَالقَوائِمُ
هَلِ الحَدَثُ الحَمراءُ تَعرِفُ لوْنَها || وَتَعْلَمُ أيُّ السّاقِيَيْنِ الغَمَائِمُ
سَقَتْها الغَمَامُ الغُرُّ قَبْلَ نُزُولِهِ || فَلَمّا دَنَا مِنها سَقَتها الجَماجِمُ
بَنَاهَا فأعْلى وَالقَنَا يَقْرَعُ القَنَا || وَمَوْجُ المَنَايَا حَوْلَها مُتَلاطِمُ
وَكانَ بهَا مثْلُ الجُنُونِ فأصْبَحَتْ || وَمِنْ جُثَثِ القَتْلى عَلَيْها تَمائِمُ
طَريدَةُ دَهْرٍ ساقَها فَرَدَدْتَهَا || على الدّينِ بالخَطّيّ وَالدّهْرُ رَاغِمُ
تُفيتُ اللّيالي كُلَّ شيءٍ أخَذْتَهُ || وَهُنّ لِمَا يأخُذْنَ منكَ غَوَارِمُ
إذا كانَ ما تَنْوِيهِ فِعْلاً مُضارِعاً || مَضَى قبلَ أنْ تُلقى علَيهِ الجَوازِمُ
وكيفَ تُرَجّي الرّومُ والرّوسُ هدمَها || وَذا الطّعْنُ آساسٌ لهَا وَدَعائِمُ
وَقَد حاكَمُوهَا وَالمَنَايَا حَوَاكِمٌ || فَما ماتَ مَظلُومٌ وَلا عاشَ ظالِمُ
أتَوْكَ يَجُرّونَ الحَديدَ كَأنّمَا || سَرَوْا بِجِيَادٍ ما لَهُنّ قَوَائِمُ
إذا بَرَقُوا لم تُعْرَفِ البِيضُ منهُمُ || ثِيابُهُمُ من مِثْلِها وَالعَمَائِمُ
خميسٌ بشرْقِ الأرْضِ وَالغرْبِ زَحْفُهُ || وَفي أُذُنِ الجَوْزَاءِ منهُ زَمَازِمُ
تَجَمّعَ فيهِ كلُّ لِسْنٍ وَأُمّةٍ || فَمَا يُفْهِمُ الحُدّاثَ إلاّ الترَاجِمُ
فَلِلّهِ وَقْتٌ ذَوّبَ الغِشَّ نَارُهُ || فَلَمْ يَبْقَ إلاّ صَارِمٌ أوْ ضُبارِمُ
تَقَطّعَ ما لا يَقْطَعُ الدّرْعَ وَالقَنَا || وَفَرّ منَ الفُرْسانِ مَنْ لا يُصادِمُ
وَقَفْتَ وَما في المَوْتِ شكٌّ لوَاقِفٍ || كأنّكَ في جَفنِ الرّدَى وهْوَ نائِمُ
تَمُرّ بكَ الأبطالُ كَلْمَى هَزيمَةً || وَوَجْهُكَ وَضّاحٌ وَثَغْرُكَ باسِمُ
تجاوَزْتَ مِقدارَ الشّجاعَةِ والنُّهَى || إلى قَوْلِ قَوْمٍ أنتَ بالغَيْبِ عالِمُ
ضَمَمْتَ جَناحَيهِمْ على القلبِ ضَمّةً || تَمُوتُ الخَوَافي تحتَها وَالقَوَادِمُ
بضَرْبٍ أتَى الهاماتِ وَالنّصرُ غَائِبٌ || وَصَارَ إلى اللّبّاتِ وَالنّصرُ قَادِمُ
حَقَرْتَ الرُّدَيْنِيّاتِ حتى طَرَحتَها || وَحتى كأنّ السّيفَ للرّمحِ شاتِمُ
وَمَنْ طَلَبَ الفَتْحَ الجَليلَ فإنّمَا || مَفاتِيحُهُ البِيضُ الخِفافُ الصّوَارِمُ
نَثَرْتَهُمُ فَوْقَ الأُحَيْدِبِ كُلّهِ || كمَا نُثِرَتْ فَوْقَ العَرُوسِ الدّراهمُ
تدوسُ بكَ الخيلُ الوكورَ على الذُّرَى || وَقد كثرَتْ حَوْلَ الوُكورِ المَطاعِمُ
تَظُنّ فِراخُ الفُتْخِ أنّكَ زُرْتَهَا || بأُمّاتِها وَهْيَ العِتاقُ الصّلادِمُ
إذا زَلِقَتْ مَشّيْتَها ببُطونِهَا || كمَا تَتَمَشّى في الصّعيدِ الأراقِمُ
أفي كُلّ يَوْمٍ ذا الدُّمُسْتُقُ مُقدِمٌ || قَفَاهُ على الإقْدامِ للوَجْهِ لائِمُ
أيُنكِرُ رِيحَ اللّيثِ حتى يَذُوقَهُ || وَقد عَرَفتْ ريحَ اللّيوثِ البَهَائِمُ
وَقد فَجَعَتْهُ بابْنِهِ وَابنِ صِهْرِهِ || وَبالصّهْرِ حَمْلاتُ الأميرِ الغَوَاشِمُ
مضَى يَشكُرُ الأصْحَابَ في فوْته الظُّبَى || لِمَا شَغَلَتْهَا هامُهُمْ وَالمَعاصِمُ
وَيَفْهَمُ صَوْتَ المَشرَفِيّةِ فيهِمِ || على أنّ أصْواتَ السّيوفِ أعَاجِمُ
يُسَرّ بمَا أعْطاكَ لا عَنْ جَهَالَةٍ || وَلكِنّ مَغْنُوماً نَجَا منكَ غانِمُ
وَلَسْتَ مَليكاً هازِماً لِنَظِيرِهِ || وَلَكِنّكَ التّوْحيدُ للشّرْكِ هَازِمُ
تَشَرّفُ عَدْنانٌ بهِ لا رَبيعَةٌ || وَتَفْتَخِرُ الدّنْيا بهِ لا العَوَاصِمُ
لَكَ الحَمدُ في الدُّرّ الذي ليَ لَفظُهُ || فإنّكَ مُعْطيهِ وَإنّيَ نَاظِمُ
وَإنّي لَتَعْدو بي عَطَايَاكَ في الوَغَى || فَلا أنَا مَذْمُومٌ وَلا أنْتَ نَادِمُ
عَلى كُلّ طَيّارٍ إلَيْهَا برِجْلِهِ || إذا وَقَعَتْ في مِسْمَعَيْهِ الغَمَاغِمُ
ألا أيّها السّيفُ الذي لَيسَ مُغمَداً || وَلا فيهِ مُرْتابٌ وَلا منْهُ عَاصِمُ
هَنيئاً لضَرْبِ الهَامِ وَالمَجْدِ وَالعُلَى || وَرَاجِيكَ وَالإسْلامِ أنّكَ سالِمُ
وَلِمْ لا يَقي الرّحمٰنُ حدّيك ما وَقى || وَتَفْليقُهُ هَامَ العِدَى بكَ دائِمُ
:::

:::paragraphs{style="note" dir=ltr}
**A note on the text.** Abū al-Ṭayyib al-Mutanabbī (915–965) recited this qaṣīda before Sayf al-Dawla, the Ḥamdānid prince of Aleppo, in 954, after the prince had rebuilt the fortress of al-Ḥadath on the Byzantine frontier and driven off the army of the Domestikos Bardas Phokas beneath its walls. It runs to forty-six bayts in the ṭawīl metre, all on one rhyme, the letter mīm. The text is the one ar.wikisource gives, with its vowels; three typing slips are corrected, in bayts 12, 16 and 46. The two lines in prose above the poem are ours.
:::

:::paragraphs{style="colophon" dir=ltr}
Set in Amiri, Aref Ruqaa and Noto Kufi Arabic (SIL OFL) · Text: al-Mutanabbī, public domain, from ar.wikisource
:::
`; // content.<lang>.md, inlined by the Cookbook

// ─── 3 · Fonts ──────────────────────────────────────────────────────────────
const FONTS = { // every face the pages use, loaded before the build (gotcha: fonts-first)
  Amiri: ['400', '400i', '700'], // NASKH: the poem, the headnote, the poet; the note's Latin
  'Aref Ruqaa': ['700'], // RUQAA: ديوان and the title
  'Noto Kufi Arabic': ['500'], // KUFI: metre, rhyme, running heads and folios
};

// ─── 4 · Build & show ───────────────────────────────────────────────────────
await loadFonts(FONTS, markdown);
// The arabic file of each face, which loadFonts leaves out (gotcha: arabic-fonts-subset).
await loadArabicFonts(FONTS, markdown);
const doc = await buildWithFonts(() => buildDocument({ markdown }, config()), markdown);
showBook(doc, { title: t({ en: 'A qasida on a diwan page',
  es: 'Una casida en una página de diván' }) });
offerPdf(() => renderToPdf(doc, { fontProvider: arabicPdfProvider }), `${RECIPE}.pdf`);

Kit · core, fonts, viewer, pdf, arabic, book: the same in every recipe · 411 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 · arabic v1 ── Arabic-script faces · postext.dev/cookbook ───────────
// Fontsource ships an Arabic family as one file per subset and weight: the
// `arabic` file holds the letters, the harakat, the Arabic-Indic digits, the
// Arabic punctuation and the presentation forms; `latin` and `latin-ext`
// hold the rest. loadFonts loads the latin files; this block adds the arabic
// file of every Arabic family, for the canvas and for the PDF, which shapes
// the letters with HarfBuzz from the same bytes.

/** The code points of Fontsource's `arabic` subset, as its stylesheets
 *  declare them (the same unicode-range the browser picks the file by). A
 *  function, not a const: the kit is inlined after the recipe's top-level
 *  awaits, and a const read before its line throws, where a function
 *  declaration is hoisted. */
function arabicRange() {
  return 'U+0600-06FF,U+0750-077F,U+0870-088E,U+0890-0891,U+0897-08E1,U+08E3-08FF,'
    + 'U+200C-200E,U+2010-2011,U+204F,U+2E41,U+FB50-FDFF,U+FE70-FE74,U+FE76-FEFC,U+102E0-102FB,'
    + 'U+10E60-10E7E,U+10EC2-10EC4,U+10EFC-10EFF,U+1EE00-1EEFF';
}

/** Whether code point `cp` is in the arabic file. */
function inArabicRange(cp) {
  inArabicRange.ranges ??= arabicRange().split(',').map((part) => {
    const [lo, hi = lo] = part.slice(2).split('-');
    return [parseInt(lo, 16), parseInt(hi, 16)];
  });
  return inArabicRange.ranges.some(([lo, hi]) => cp >= lo && cp <= hi);
}

/** Whether Fontsource serves `family` with an `arabic` subset. Fails when
 *  the API does not answer: an Arabic face taken for a Latin one would set
 *  its letters in a system face. */
async function isArabicFamily(family) {
  const meta = await fontsourceMeta(family);
  if (!meta) throw new Error(`api.fontsource.org did not describe ${family}: reload to try again`);
  return !!meta.subsets?.includes('arabic');
}

/** The arabic file of a face. */
function arabicFileUrl(family, weight, style) {
  const id = fontsourceId(family);
  return `https://cdn.jsdelivr.net/npm/@fontsource/${id}@5/files/${id}-arabic-${weight}-${style}.woff2`;
}

/** faces = { Amiri: ['400', '700'] }, as for loadFonts, after it: the whole
 *  FONTS object may be passed, its families without an arabic subset are
 *  left alone. Adds the arabic file of every listed weight of each Arabic
 *  family (the latin files come from loadFonts) and loads it. `text` is
 *  the sample: fails when it holds an Arabic-script character the arabic
 *  file does not cover. List every weight the pages set in Arabic: a weight
 *  left to buildWithFonts gets the latin file only, and its Arabic letters
 *  fall back to a system face. Resolves to the number of files loaded. */
async function loadArabicFonts(faces, text = '') {
  kitStatus('Loading fonts…');
  let loaded = 0;
  try {
    const outside = [...new Set(text)].filter((ch) => /\p{Script=Arabic}/u.test(ch) && !inArabicRange(ch.codePointAt(0)));
    if (outside.length) throw new Error(`Fontsource's arabic files have no ${outside.slice(0, 12).join(' ')}`);
    for (const [family, specs] of Object.entries(faces)) {
      if (!(await isArabicFamily(family))) continue;
      for (const spec of new Set(specs)) {
        const weight = parseInt(spec, 10);
        const style = spec.endsWith('i') ? 'italic' : 'normal';
        const face = new FontFace(family, `url(${arabicFileUrl(family, weight, style)}) format('woff2')`,
          { weight: String(weight), style, unicodeRange: arabicRange() });
        document.fonts.add(await face.load().catch(() => {
          throw new Error(`Fontsource has no arabic file for ${family} ${weight} ${style}`);
        }));
        loaded++;
      }
    }
  } catch (error) {
    kitFail(error);
    throw error;
  }
  return loaded;
}

/** The PDF font provider for recipes with Arabic faces: a family with an
 *  arabic subset gets its arabic file when its pages set Arabic letters
 *  (`request.codePoints`), then its latin file, and its latin-ext file for
 *  the letters beyond latin (transliteration: ā ḥ ʿ). The arabic file comes
 *  first: it also holds the space and the brackets, so a line of Arabic is
 *  shaped as one run and not cut at every space. Any other family goes to
 *  fontsourceProvider (the "pdf" block). */
async function arabicPdfProvider(family, weight, style, request) {
  if (!(await isArabicFamily(family))) return fontsourceProvider(family, weight, style);
  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.styles.includes('italic') ? 'normal' : style;
  const wanted = [...(request?.codePoints ?? [])];
  const id = fontsourceId(family);
  const urls = [];
  if (!wanted.length || wanted.some(inArabicRange)) urls.push(arabicFileUrl(family, w, s));
  urls.push(`https://cdn.jsdelivr.net/npm/@fontsource/${id}@5/files/${id}-latin-${w}-${s}.woff2`);
  if (meta.subsets.includes('latin-ext') && wanted.some((cp) => /[Ā-˿Ḁ-ỿ]/u.test(String.fromCodePoint(cp)))) {
    urls.push(`https://cdn.jsdelivr.net/npm/@fontsource/${id}@5/files/${id}-latin-ext-${w}-${s}.woff2`);
  }
  return Promise.all(urls.map(async (url) => {
    const res = await fetch(url);
    if (!res.ok) throw new Error(`Fontsource file ${url} (${res.status})`);
    return decompressWoff2(new Uint8Array(await res.arrayBuffer()));
  }));
}

// ─── Kit · book v1 ── books bound on either edge · postext.dev/cookbook ──────
// A book bound on the right (Arabic, Hebrew or Persian text, vertical
// Chinese, or page.binding 'right') opens from what a Latin reader calls
// the back: page 1 lies alone on the left of the spine, then [3 | 2].

/** showPages for a book bound on either edge. A right-bound book (the
 *  document says so: doc.binding is 'right' for page.binding 'right', for
 *  text that runs right to left and for vertical text, when the binding is
 *  left to 'auto') lies on the desk as it opens: page 1 alone on the left
 *  of the spine, then [3 | 2], the spine shade on each page's inner edge.
 *  `binding` ('left' | 'right') overrides the document's. */
function showBook(docs, { binding, ...options } = {}) {
  const count = showPages(docs, options);
  const right = (binding ?? [docs].flat()[0]?.binding) === 'right';
  if (!document.getElementById('pt-kit-book')) {
    // The pages keep direction ltr, as in a left-bound book: a canvas takes
    // the direction its element inherits, and under the spread's rtl a run
    // painted for an ltr canvas would end where the engine starts it.
    document.head.insertAdjacentHTML('beforeend', `<style id="pt-kit-book">
      .pt-spread[dir="rtl"] canvas { direction: ltr; }
      .pt-spread[dir="rtl"] 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); }
    </style>`);
  }
  // Each pair stays [verso, recto] in the page; right to left, the verso
  // sits on the right. Phones stack the pages in reading order either way.
  for (const spread of document.querySelectorAll('#pages > .pt-spread')) spread.dir = right ? 'rtl' : 'ltr';
  document.getElementById('pages').dataset.binding = right ? 'right' : 'left';
  return count;
}

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