Haicais e tankas compostos na vertical

// ═══ Postext Cookbook · Nº 119 · Haiku and tanka set vertically ═══════════════════
// https://postext.dev/en/cookbook/haiku-and-tanka
// Code: MIT · Text: 芭蕉『おくのほそ道』, 啄木『一握の砂』, Aozora Bunko (PD) · Pictures: none
// Fonts: Shippori Mincho, Noto Sans JP (SIL OFL 1.1) · Needs postext ≥ 1.16.1
import {
  buildDocument, renderPageToCanvas, clearMeasurementCache, loadVerticalAlternates,
} from 'https://esm.sh/postext';
import { renderToPdf, decompressWoff2 } from 'https://esm.sh/postext-pdf';

const LANG = 'en'; // @lang: the language of the colophon; the poems are Japanese in both
const RECIPE = 'haiku-and-tanka';

// ─── 1 · Design ─────────────────────────────────────────────────────────────
// #region palette: ink, one persimmon, a soft poetry stock
const palette = {
  ink: '#22201d', // the poems
  persimmon: '#b5512c', // 柿: the part titles' rule and the ornaments
  muted: '#6a645c', // the hashira, the folios, the colophon
  paper: '#fbf8f1',
};
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: 'defaults', value: { hex: palette.persimmon, model: 'hex' } },
];
// #endregion
// Shippori Mincho: it has the 〻 of 日〻 and 人〻, which Zen Old Mincho lacks.
const [MINCHO, GOTHIC] = ['Shippori Mincho', 'Noto Sans JP'];
const [BODY, LEAD, CHARS, LINES] = [10, 19, 36, 14]; // pt, pt: 36字 × 14行, a 1.9 em pitch
const lines = (n) => pt(n * LEAD);

// #region answer: a haiku on one line three characters down, a tanka in three, 地付き names
// Each line of verse is a paragraph of its own, so a style sets where it starts. A haiku
// stands three characters down from the head of the line; Takuboku's tanka keep his three
// lines, two down; 曾良 signs his haiku raised five characters from the foot (地から五字上げ).
const paragraphStyles = [
  { id: 'haiku', indent: em(3), firstLineIndent: em(0), marginTop: pt(0), marginBottom: pt(0) },
  { id: 'tanka', indent: em(2), firstLineIndent: em(0), marginTop: pt(0), marginBottom: pt(0) },
  { id: 'by', textAlign: 'end', endIndent: em(5), firstLineIndent: em(0) },
  // The ornament between groups of poems, in the middle of its line.
  { id: 'ornament', textAlign: 'center', firstLineIndent: em(0), color: col('persimmon') },
];
//   :::paragraphs{style="haiku"}       :::paragraphs{style="by"}
//   夏草や兵どもが夢の跡                   曾良
//   :::                                :::
// #endregion

// #region tanka: a box with nothing drawn round it keeps each tanka on one page
// Postext has no hard line break and never keeps one paragraph with the next, so each tanka
// sits in a box with nothing drawn round it: a box moves on whole (keepTogether, its
// default), and a tanka is never cut at the foot of a page. One blank line follows each.
//   :::callout{type="tanka"}  :::paragraphs{style="tanka"} … three lines …  :::  :::
const calloutStyles = [{ id: 'tanka', backgroundEnabled: false, keepTogether: true,
  padding: { top: pt(0), right: pt(0), bottom: pt(0), left: pt(0) },
  marginTop: pt(0), marginBottom: pt(LEAD),
  body: { fontFamily: MINCHO, fontSize: pt(BODY), lineHeight: pt(LEAD), color: col('ink'),
    firstLineIndent: em(0) } }];
// #endregion

// #region places: the place names take two lines, spaced to three characters
// The place names over the prose take two lines (2行取り), four characters down, and a
// two-character name is spaced out to three (字取り: 平泉 → 平　泉), so they all end level.
const place = {
  level: 2, fontFamily: MINCHO, fontWeight: 700, fontSize: pt(11),
  lineSpan: 2, indent: em(4), jidori: 3,
};
// #endregion

// #region part: each part opens a page with its title, （抄） and the poet at the foot
// A design on a vertical page is laid out in the flow frame: x runs down the column from
// the head of the type area, y across the page leftwards from its right edge.
const at = (down, across) => ({ anchor: { to: 'container', edge: 'top-left' },
  offset: { x: pt(down), y: pt(across) } });
const TITLE = 18; // pt
const part = {
  level: 1, breakBefore: { enabled: true, parity: 'any' }, // gotcha: headings-drop-h1-break
  advancedDesign: { enabled: true, minHeight: lines(5), slot: { elements: [
    { kind: 'text', id: 'title', content: '{titleText}', fontFamily: MINCHO, fontWeight: 700,
      fontSize: pt(TITLE), lineHeight: 1, letterSpacing: pt(4), color: col('ink'),
      placement: at(3 * BODY, 1.5 * LEAD - TITLE / 2) },
    { kind: 'text', id: 'abridged', content: '（抄）', fontFamily: MINCHO, fontSize: pt(9),
      color: col('ink'), placement: { anchor: { to: '#title', edge: 'right-of' },
        offset: { x: pt(6), y: pt((TITLE - 9) / 2) } } },
    { kind: 'rule', id: 'rule', direction: 'horizontal', thickness: pt(0.6),
      color: col('persimmon'), placement: { ...at(3 * BODY, 2.5 * LEAD),
        size: { width: pt(4 * TITLE) } } },
    { kind: 'text', id: 'poet', content: '{attr.author}', fontFamily: MINCHO, fontSize: pt(11),
      letterSpacing: pt(3), color: col('ink'),
      placement: at(CHARS * BODY - 4 * 11 - 3 * 3 - 2 * BODY, 3.5 * LEAD - 11 / 2) },
  ] } },
};
// #endregion

// #region furniture: the book's title down the fore-edge, the folio below it
const foreEdge = (id, content, parity, edge, y, extra = {}) => ({
  kind: 'text', id, content, parity, pages: 'body', writingMode: 'vertical-rl',
  fontFamily: GOTHIC, fontSize: pt(7), letterSpacing: pt(1), color: col('muted'),
  overflow: 'clip', placement: { anchor: { to: 'outer', edge }, offset: { y: em(y) } },
  ...extra,
});
const header = { elements: [
  foreEdge('book', '{title}', 'even', 'top', 3),
  foreEdge('part', '{chapterTitle}', 'odd', 'top', 3),
  foreEdge('folio', '{pageNumber}', 'all', 'bottom', -3, { pages: 'all' }),
] };
const none = { elements: [] };
// The first part's opening page carries the colophon across the foot.
const first = { id: 'first', footer: { elements: [{ kind: 'text', id: 'colophon',
  content: '{attr.colophon}', pages: 'opener', fontFamily: GOTHIC, fontSize: pt(5.5),
  lineHeight: 1.45, color: col('muted'), overflow: 'wrap', align: 'center',
  placement: { anchor: { to: 'page', edge: 'bottom' }, offset: { y: mm(-7) },
    size: { width: mm(100) } } }] } };
// #endregion

const config = () => ({ // a factory: the engine caches resolved configs per object
  locale: 'ja', // written out, never LANG (gotcha: ja-locale-tag)
  colorPalette,
  page: {
    sizePreset: 'custom', width: mm(127), height: mm(188), dpi: 150, // 四六判
    backgroundColor: col('paper'),
    margins: { top: mm(32), bottom: mm(24), left: mm(15), right: mm(17), mirror: true },
    pageNumbering: { format: 'japanese-informal' },
  },
  layout: { layoutType: 'single', writingMode: 'vertical-rl' },
  cjk: { grid: { enabled: true, charsPerLine: CHARS, linesPerPage: LINES } },
  bodyText: {
    fontFamily: MINCHO, fontSize: pt(BODY), lineHeight: pt(LEAD), color: col('ink'),
    boldColor: col('ink'), italicColor: col('ink'), referenceColor: col('ink'),
    textAlign: 'justify', firstLineIndent: em(1), indentAfterHeading: true,
  },
  headings: { fontFamily: MINCHO, color: col('ink'), levels: [part, place] },
  headingStyles: [first],
  paragraphStyles,
  calloutStyles,
  header,
  footer: none,
});

// ─── 2 · Content ────────────────────────────────────────────────────────────
const markdown = String.raw`---
Amostra em Markdown · 183 linhas · content.en.md
title: "芭蕉と啄木"
subtitle: "俳句と短歌"
---

# おくのほそ道 {style="first" author="松尾芭蕉" colophon="Matsuo Bashō, おくのほそ道 (The Narrow Road to the Deep North, 1702), selections, after Sugiura Shōichirō’s 1957 edition; Ishikawa Takuboku, 一握の砂 (A Handful of Sand, 1910), twelve tanka. Text: Aozora Bunko 61619 and 816, public domain. Set in Shippori Mincho and Noto Sans JP (SIL OFL)."}

## 冒頭

{月日|つきひ}は{百代|はくだい}の{過客|くわかく}にして、{行|ゆき}かふ{年|とし}も{又|また}{旅人|たびびと}{也|なり}。{舟|ふね}の{上|うへ}に生涯をうかべ馬の口とら{え|（へ）}て{老|おい}をむかふる{物|もの}は、{日〻|ひび}{旅|たび}にして{旅|たび}を{栖|すみか}とす。古人も多く旅に死せるあり。予もいづれの年よりか、{片雲|へんうん}の風にさそはれて、漂泊の思ひやまず海濱にさすらへ、{去年|こぞ}の秋{江上|かうじやう}の{破屋|はをく}に{蜘|くも}の古巣をはらひて、やゝ年も{暮|くれ}春{立|たて}る霞の空に白川の關こえんと、そゞろ{神|がみ}の物につきて心をくるはせ、{道祖神|だうそじん}のまねきにあひて{取|とる}もの手につかず、もゝ{引|ひき}の{破|やぶれ}をつゞり{笠|かさ}の{緒|を}{付|つけ}か{え|（へ）}て、三里に灸す{ゆ|（う）}るより松嶋の月{先|まづ}心にかゝりて、{住|すめ}る{方|かた}は人に讓り{杉風|さんぷう}が{別墅|べつしよ}に移るに、

:::paragraphs{style="haiku"}
草の戸も{住替|すみかは}る{代|よ}ぞひなの家
:::

{面八句|おもてはちく}を{庵|いほり}の柱に{懸置|かけおく}。

## 旅立

:::paragraphs{style="haiku"}
{行|ゆく}春や鳥{啼|なき}{魚|うを}の目は{泪|なみだ}
:::

## 平泉

三代の{榮耀|えいえう}{一睡|いつすゐ}の{中|うち}にして、{大門|だいもん}の跡は一里こなたに{有|あり}。{秀衡|ひでひら}が跡は田野に{成|なり}て、金鷄山のみ形を殘す。{先|まづ}{高舘|たかだち}にのぼれば、北上川南部より流るゝ{大河|たいが}也。衣川は和泉が{城|じやう}をめぐりて、高舘の下にて大河に{落入|おちいる}。{康衡|やすひら}等が旧跡は、衣が關を{隔|へだて}て南部口をさし堅め、{夷|えぞ}をふせぐとみえたり。{偖|さて}も義臣すぐつて{此城|このしろ}にこもり、功名一時の{叢|くさむら}となる。「國破れて山河あり、{城|じやう}春にして草青みたり」と笠{打敷|うちしき}て時のうつるまで泪を落し侍りぬ。

:::paragraphs{style="haiku"}
{夏草|なつくさ}や{兵|つはもの}どもが夢の跡

{卯|う}の{花|はな}に{兼房|かねふさ}みゆる{白毛|しらが}かな
:::

:::paragraphs{style="by"}
曾良
:::

## 立石寺

山形領に{立石寺|りふしやくじ}と{云|いふ}山寺あり。{慈覺大師|じかくだいし}の開基にして、{殊|ことに}清閑の地也。一見すべきよし、人〻のすゝむるに{依|よつ}て、尾花澤よりとつて返し、{其|その}間七里ばかり也。日いまだ{暮|くれ}ず。{麓|ふもと}の坊に宿かり{置|おき}て、山上の堂にのぼる。岩に{巖|いはほ}を{重|かさね}て山とし、{松柏|しようはく}{年旧|としふり}、{土石|どせき}{老|おい}て苔{滑|なめらか}に、岩上の院〻{扉|とびら}を{閉|とぢ}て物の音きこえず。{岸|きし}をめぐり岩を{這|はひ}て{佛閣|ぶつかく}を拜し、{佳景|かけい}{寂莫|じやくまく}として心すみ{行|ゆく}のみおぼゆ。

:::paragraphs{style="haiku"}
{閑|しづか}さや岩にしみ{入|いる}蝉の聲
:::

## 最上川

:::paragraphs{style="haiku"}
五月雨をあつめて早し最上川
:::

## 越後路

:::paragraphs{style="haiku"}
文月や六日も常の夜には似ず

荒海や佐渡によこたふ{天河|あまのがは}
:::

## 大垣

:::paragraphs{style="haiku"}
蛤のふたみにわかれ{行|ゆく}秋ぞ
:::

# 一握の砂 {author="石川啄木"}

:::callout{type="tanka"}
:::paragraphs{style="tanka"}
{東海|とうかい}の{小島|こじま}の{磯|いそ}の{白砂|しらすな}に

われ{泣|な}きぬれて

{蟹|かに}とたはむる
:::
:::

:::callout{type="tanka"}
:::paragraphs{style="tanka"}
{頬|ほ}につたふ

なみだのごはず

{一握|いちあく}の砂を{示|しめ}しし人を忘れず
:::
:::

:::callout{type="tanka"}
:::paragraphs{style="tanka"}
いのちなき砂のかなしさよ

さらさらと

{握|にぎ}れば指のあひだより落つ
:::
:::

:::callout{type="tanka"}
:::paragraphs{style="tanka"}
たはむれに母を{背負|せお}ひて

そのあまり{軽|かろ}きに泣きて

三歩あゆまず
:::
:::

:::callout{type="tanka"}
:::paragraphs{style="tanka"}
はたらけど

はたらけど{猶|なほ}わが{生活|くらし}楽にならざり

ぢっと手を見る
:::
:::

:::paragraphs{style="ornament"}
＊
:::

:::callout{type="tanka"}
:::paragraphs{style="tanka"}
{不来方|こずかた}のお城の草に寝ころびて

空に吸はれし

{十五|じふご}の心
:::
:::

:::callout{type="tanka"}
:::paragraphs{style="tanka"}
ふるさとの{訛|なまり}なつかし

{停車場|ていしやば}の人ごみの中に

そを{聴|き}きにゆく
:::
:::

:::callout{type="tanka"}
:::paragraphs{style="tanka"}
石をもて追はるるごとく

ふるさとを{出|い}でしかなしみ

消ゆる時なし
:::
:::

:::callout{type="tanka"}
:::paragraphs{style="tanka"}
やはらかに柳あをめる

{北上|きたかみ}の{岸辺|きしべ}目に見ゆ

泣けとごとくに
:::
:::

:::callout{type="tanka"}
:::paragraphs{style="tanka"}
ふるさとの山に向ひて

言ふことなし

ふるさとの山はありがたきかな
:::
:::

:::paragraphs{style="ornament"}
＊
:::

:::callout{type="tanka"}
:::paragraphs{style="tanka"}
{函館|はこだて}の{青柳町|あをやぎちやう}こそかなしけれ

友の{恋歌|こひうた}

矢ぐるまの花
:::
:::
`; // content.<lang>.md: the same Japanese text in both

// ─── 3 · Fonts ──────────────────────────────────────────────────────────────
const FONTS = {
  'Shippori Mincho': ['400', '700'], // the poems and the prose; the titles
  'Noto Sans JP': ['400'], // the hashira, the folios and the colophon
};

// ─── 4 · Build & show ───────────────────────────────────────────────────────
// #region voices: each face loads the files that hold the characters it sets
const title = markdown.match(/^title: "(.*)"$/m)[1];
const heads = markdown.match(/^#+ [^{\n]*/gm).join('');
await loadFonts(FONTS, markdown); // the Latin files: the colophon
await loadCjkFonts({ [MINCHO]: ['400'] }, markdown, { vertical: true });
await loadCjkFonts({ [MINCHO]: ['700'] }, heads);
await loadCjkFonts({ [GOTHIC]: ['400'] },
  `${title}${heads}${markdown.match(/colophon="([^"]*)"/)[1]}一二三四五六七八九十`, { vertical: true });
// #endregion
const doc = await buildWithFonts(() => buildDocument({ markdown }, config()), markdown);
showBook(doc, { title: t({ en: 'Haiku and tanka set vertically',
  es: 'Haikus y tankas compuestos en vertical' }) });
offerPdf(() => renderToPdf(doc, { fontProvider: cjkPdfProvider }), `${RECIPE}.pdf`);

Kit · core, fonts, viewer, pdf, cjk: igual em todas as receitas · 459 linhas
// ─── 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 v2 ── the same in every recipe · postext.dev/cookbook
// Postext measures with the loaded faces and caches the widths: load every face
// before the first build, from Fontsource, the files the PDF embeds too.

/** faces = { 'Family Name': ['400', '400i', '700'] }. `text` is the sample:
 *  č ł † α χ also load latin-ext and greek files (kitSubsetsFor). 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',
    greek: 'U+0370-03FF',
  };
  const jobs = [];
  let added = 0;
  for (const [family, specs] of Object.entries(faces)) {
    const id = fontsourceId(family);
    const todo = [...new Set(specs)].map((spec) => [parseInt(spec, 10), spec.endsWith('i') ? 'italic' : 'normal'])
      .filter(([weight, style]) => !hasFace(family, weight, style)); // before any await
    const meta = optional || /[^\0-ÿ]/u.test(text) ? await fontsourceMeta(family) : null;
    const subsets = ['latin', ...kitSubsetsFor(text, meta)];
    for (const [weight, style] of todo) {
      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` and loads any face the pages use that FONTS missed (a regular
 *  one with a warning), then clears the measurement cache and builds 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. */
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' };
}

/** A loaded FontFace covers this family, weight and style (fonts.check() would
 *  also say yes 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;
}

/** The files beyond latin `text` needs that `meta`'s family ships. */
function kitSubsetsFor(text, meta) {
  return [[/[Ā-˿ᴀ-ᶿḀ-ỿ†ℓⱠ-Ɀ꜠-ꟿ]/u, 'latin-ext'], [/[Ͱ-Ͽ]/u, 'greek']]
    .filter(([re, x]) => re.test(text) && meta?.subsets?.includes(x)).map(([, x]) => x);
}

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

/** The family's Fontsource metadata (weights, styles, subsets), 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
/** The pages as spreads on a dark desk, page 1 alone, then verso | recto,
 *  each painted when it scrolls near. */
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 v2 ── the same in every recipe that exports a PDF
/** The Fontsource files the screen used, as TrueType: the nearest weight the
 *  family ships, upright if it has no italic; latin, then what the face's
 *  letters need (kitSubsetsFor). */
async function fontsourceProvider(family, weight, style, request) {
  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 text = String.fromCodePoint(...(request?.codePoints ?? []));
  const more = kitSubsetsFor(text, meta);
  const files = await Promise.all(['latin', ...more].map(async (subset) => {
    const res = await fetch(`https://cdn.jsdelivr.net/npm/@fontsource/${id}@5/files/${id}-${subset}-${w}-${s}.woff2`);
    if (!res.ok) throw new Error(`Fontsource has no ${family} ${w} ${s} ${subset}`);
    return decompressWoff2(new Uint8Array(await res.arrayBuffer()));
  }));
  return files.length === 1 ? files[0] : files;
}

/** A "Build the PDF" button; then "Open the PDF" (a new tab: CodePen's frame
 *  shows no 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 · cjk v1 ── Chinese, Japanese and Korean books · postext.dev/cookbook
// Fontsource ships a CJK family as about a hundred files per weight, each
// declared in its stylesheet with the unicode-range it covers. The screen
// loads the files the sample touches; the PDF gets the same files for the
// characters its pages set in each face, and embeds each as a subset.
// A book bound on the right (vertical text) is shown with its spreads
// mirrored: page 1 alone on the left of the spine, then [3 | 2].

/** The files of a Fontsource face, read from its stylesheet: { url, range,
 *  ranges }, the last declared first (the order the browser tries them in). */
function cjkSlices(family, weight, style) {
  cjkSlices.cache ??= new Map();
  const id = fontsourceId(family);
  const css = `https://cdn.jsdelivr.net/npm/@fontsource/${id}@5/${weight}${style === 'italic' ? '-italic' : ''}.css`;
  if (!cjkSlices.cache.has(css)) {
    cjkSlices.cache.set(css, fetch(css)
      .then((res) => {
        if (!res.ok) throw new Error(`Fontsource has no ${family} ${weight} ${style} (${res.status})`);
        return res.text();
      })
      .then((text) => [...text.matchAll(/@font-face\s*{([^}]*)}/g)].map(([, rule]) => {
        const range = /unicode-range:\s*([^;]+);/.exec(rule)?.[1].trim() ?? 'U+0-10FFFF';
        const ranges = range.split(',').map((part) => {
          const [lo, hi = lo] = part.trim().slice(2).split('-');
          return [parseInt(lo, 16), parseInt(hi, 16)];
        });
        return { url: new URL(/url\(([^)]+?\.woff2)\)/.exec(rule)[1], css).href, range, ranges };
      }).reverse()));
  }
  return cjkSlices.cache.get(css);
}

/** The file of `slices` that holds code point `cp`, if any. */
function cjkSliceFor(slices, cp) {
  return slices.find((slice) => slice.ranges.some(([lo, hi]) => cp >= lo && cp <= hi));
}

/** Whether Fontsource serves `family` as a Chinese, Japanese or Korean
 *  family (its subsets name the script). Fails when the API does not
 *  answer: a CJK face taken for a Latin one would paint in a system face. */
async function isCjkFamily(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?.some((subset) => /^(chinese|japanese|korean)/.test(subset));
}

/** faces = { 'Noto Serif TC': ['400', '700'] }, as for loadFonts: the
 *  whole FONTS object may be passed, its other families are left to
 *  loadFonts. Adds one FontFace per file of each CJK face with its
 *  unicodeRange, then loads the files `text` touches. `text` is what the
 *  faces set: the sample for the text face; a book in several voices calls
 *  it once per voice (loadCjkFonts({ 'LXGW WenKai TC': ['400'] }, quotes)),
 *  so the heading and quotation faces fetch and check only their own
 *  characters. Fails when a character of `text` is in no file of a face.
 *  List every weight the pages use: a weight left to buildWithFonts gets
 *  the latin file only. With { vertical: true } it also loads each
 *  family's vertical forms (brackets, quotes, pause marks) for the canvas,
 *  which needs loadVerticalAlternates imported from postext. Resolves to
 *  the number of files loaded. */
async function loadCjkFonts(faces, text, { vertical = false } = {}) {
  kitStatus('Loading fonts…');
  let loaded = 0;
  try {
    if (vertical && typeof loadVerticalAlternates !== 'function') {
      throw new Error('loadCjkFonts(…, { vertical: true }) needs loadVerticalAlternates imported from postext');
    }
    for (const [family, specs] of Object.entries(faces)) {
      if (!(await isCjkFamily(family))) continue;
      const twin = [];
      for (const spec of new Set(specs)) {
        const weight = parseInt(spec, 10);
        const style = spec.endsWith('i') ? 'italic' : 'normal';
        const slices = await cjkSlices(family, weight, style);
        const missing = [...new Set(text)].filter((ch) => /\S/.test(ch) && !cjkSliceFor(slices, ch.codePointAt(0)));
        if (missing.length) {
          throw new Error(`${family} ${spec} has no file for ${missing.slice(0, 12).join(' ')}: `
            + `give each face the text it sets (loadCjkFonts({ '${family}': ['${spec}'] }, text))`);
        }
        for (const slice of slices) {
          document.fonts.add(new FontFace(family, `url(${slice.url}) format('woff2')`,
            { weight: String(weight), style, unicodeRange: slice.range }));
          twin.push({ source: slice.url, weight: String(weight), style, unicodeRange: slice.range });
        }
        const font = `${style === 'italic' ? 'italic ' : ''}${weight} 16px "${family}"`;
        loaded += (await document.fonts.load(font, text)).length;
        if (!document.fonts.check(font, text)) throw new Error(`${family} ${spec} did not load for the sample`);
      }
      // The same files under a twin name with the `vert` feature on: the
      // canvas paints the punctuation of vertical lines with it.
      if (vertical && twin.length) await loadVerticalAlternates(family, twin);
    }
  } catch (error) {
    kitFail(error);
    throw error;
  }
  return loaded;
}

/** The PDF font provider for recipes with CJK faces: a family whose
 *  Fontsource subsets are Chinese, Japanese or Korean gets the files that
 *  hold the characters its pages set (`request.codePoints`); any other
 *  family gets the latin file fontsourceProvider fetches (the "pdf" block)
 *  and, when the face sets letters only latin-ext has, that file too. */
async function cjkPdfProvider(family, weight, style, request) {
  if (!(await isCjkFamily(family))) return cjkLatinPdfFiles(family, weight, style, request);
  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 slices = await cjkSlices(family, w, s);
  const picked = new Set();
  for (const cp of request?.codePoints ?? []) {
    const slice = cjkSliceFor(slices, cp);
    if (slice) picked.add(slice);
  }
  if (!picked.size) picked.add(slices[0]);
  return Promise.all(slices.filter((slice) => picked.has(slice)).map(async (slice) => {
    const res = await fetch(slice.url);
    if (!res.ok) throw new Error(`Fontsource file ${slice.url} (${res.status})`);
    return decompressWoff2(new Uint8Array(await res.arrayBuffer()));
  }));
}

/** A Latin family set next to the CJK faces: its latin file, then its
 *  latin-ext file when the face sets letters only latin-ext has (ō ū in
 *  Hepburn rōmaji, ǎ in pinyin), the file loadFonts adds on screen for
 *  them. Latin comes first: postext-pdf draws a character from the first
 *  file that has it, as the browser takes a character both files hold from
 *  latin. A face Fontsource ships without latin-ext, or whose file does
 *  not come, gets latin alone, and the PDF names the letters it lacks. */
async function cjkLatinPdfFiles(family, weight, style, request) {
  const meta = await fontsourceMeta(family);
  const beyond = [...(request?.codePoints ?? [])].some(cjkLatinExtOnly);
  if (!beyond || !meta?.subsets?.includes('latin-ext')) return fontsourceProvider(family, weight, style);
  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 id = fontsourceId(family);
  const url = `https://cdn.jsdelivr.net/npm/@fontsource/${id}@5/files/${id}-latin-ext-${w}-${s}.woff2`;
  const [latin, ext] = await Promise.all([fontsourceProvider(family, weight, style), fetch(url)
    .then(async (res) => (res.ok ? decompressWoff2(new Uint8Array(await res.arrayBuffer())) : null), () => null)]);
  return ext ? [latin, ext] : latin;
}

/** Whether code point `cp` is in Fontsource's latin-ext file and not in
 *  its latin file: Latin Extended-A and -B, IPA, the spacing modifiers and
 *  Latin Extended Additional (loadFonts's test for latin-ext), less the
 *  few latin holds too (ı Œ œ ʻ ʼ ˆ ˚ ˜). */
function cjkLatinExtOnly(cp) {
  if (!((cp >= 0x100 && cp <= 0x2ff) || (cp >= 0x1e00 && cp <= 0x1eff))) return false;
  return ![0x131, 0x152, 0x153, 0x2bb, 0x2bc, 0x2c6, 0x2da, 0x2dc].includes(cp);
}

/** showPages for a book bound on either edge. A right-bound book (the
 *  document says so: doc.binding is 'right' for page.binding 'right' and
 *  for vertical text) 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-cjk')) {
    // The pages keep direction ltr: a canvas draws text in the direction its
    // element inherits, and under rtl each run would end where the engine
    // starts it, its brackets mirrored.
    document.head.insertAdjacentHTML('beforeend', `<style id="pt-kit-cjk">
      .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 ───────────────────────────────────────────────────────────────────────