A vertical newspaper page in tiers

// ═══ Postext Cookbook · Nº 084 · A vertical newspaper page in tiers ═══════════════
// https://postext.dev/en/cookbook/vertical-newspaper-tiers
// Code: MIT · Text: Shenbao, 1912 (PD); gazette, stele report: zh.wikisource (CC BY-SA 4.0)
// Fonts: Noto Serif TC, Noto Sans TC, LXGW WenKai TC (SIL OFL 1.1) · Needs postext ≥ 1.9.0
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 news is Chinese in both editions
const RECIPE = 'vertical-newspaper-tiers';

// ─── 1 · Design ─────────────────────────────────────────────────────────────
// #region palette: newsprint, ink and the vermilion of the masthead
const palette = {
  ink: '#1c1a17', // text, the rules between tiers
  accent: '#b0281c', // the one accent: the masthead block, the telegrams' flag
  rule: '#8f887c', // the hairline before each story
  muted: '#5e574e', // datelines, sources, the colophon
  paper: '#f7f2e6', // newsprint, and the masthead's type reversed out of the vermilion
};
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: 'ink (defaults)', value: { hex: palette.ink, model: 'hex' } },
];
// #endregion

const [SONG, HEI, KAI] = ['Noto Serif TC', 'Noto Sans TC', 'LXGW WenKai TC']; // 宋, 黑, 楷
const BODY = 10.5; // pt: 五號, the body size of the papers of 1912
const LEAD = 15.75; // pt: the line pitch across the page, 1.5 em
const CHARS = 25; // characters down a tier: a newspaper column, 17 to 25
const HEIGHT = 2 * CHARS * BODY + 2 * BODY; // pt: two tiers and a gutter of two ems
const TRIM = { w: 184, h: 260 }; // mm, 16開
const MARGIN = { top: 30, bottom: 22, side: 11 }; // mm, minimums: the grid centres the tiers
// The grid grows the margins evenly, so the tiers start HEAD mm below the top edge.
const HEAD = MARGIN.top + (TRIM.h - MARGIN.top - MARGIN.bottom - (HEIGHT * 25.4) / 72) / 2;

// #region answer: two tiers down the page with a rule between them, three inside a box
// On a vertical page two columns are two tiers (欄), stacked and filled from the upper right:
// the gutter is the gap between them, the column rule a rule across the page.
const layout = {
  layoutType: 'double', writingMode: 'vertical-rl', // binding 'auto' becomes 'right'
  gutterWidth: pt(2 * BODY),
  columnRule: { enabled: true, color: col('ink'), lineWidth: pt(0.75) },
};
// The grid counts characters down a tier and lines across the page: 25 × 29.
const cjk = { grid: { enabled: true, charsPerLine: CHARS, linesPerPage: 29 } };
// The body has two tiers at most. The telegrams take three inside a page-span box floated to
// the foot of the flow, the left of the sheet (gotcha: callout-columns), with the fences
//   :::callout{type="wires" span="page" placement="bottom" title="電報"} and :::columns{count=3}
const wires = { id: 'wires', backgroundEnabled: false,
  stripe: { enabled: true, side: 'top', width: pt(1.5), color: col('ink') }, // on its right
  padding: { top: pt(6), right: pt(0), bottom: pt(0), left: pt(0) },
  columnGap: pt((HEIGHT - 3 * 18 * 9) / 2), // three tiers of 18 characters of 9 pt
  titleStyle: { fontFamily: HEI, fontSize: pt(12), fontWeight: 700, color: col('accent') },
  body: { fontFamily: SONG, fontSize: pt(9), lineHeight: pt(13.5), textAlign: 'justify',
    firstLineIndent: pt(0), boldFontWeight: 700 } };
// #endregion

// In the flow of a vertical page x runs down the sheet and y leftward from its right edge.
const at = (x, y, extra = {}) => ({ anchor: { to: 'container', edge: 'top-left' },
  offset: { x: pt(x), y: pt(y) }, ...extra });
const text = (id, content, family, weight, size, colour, extra = {}) => ({ kind: 'text', id,
  content, fontFamily: family, fontWeight: weight, fontSize: pt(size), lineHeight: 1.2,
  color: col(colour), align: 'left', overflow: 'wrap', ...extra });
const below = (id, y, extra = {}) => ({ anchor: { to: `#${id}`, edge: 'below' },
  offset: { y: pt(y) }, ...extra }); // y more points across the page, leftward
const fill = { size: { width: 'fill' } };

// #region front: the masthead and the lead headline, one design down the right of page 1
// A page-span heading always opens a page (gotcha: page-span-heading-new-page), so the lead
// story's H1 carries the masthead in its own design, above its headline.
const MAST = 6.5 * LEAD; // the masthead's block, across the page
const block = (id, inset, style) => ({ kind: 'box', id, style,
  placement: at(inset, inset, { size: { width: pt(HEIGHT - 2 * inset),
    height: pt(MAST - 2 * inset) } }) });
const BAND = 13 * LEAD; // the whole design: masthead, headline, deck
const front = { enabled: true, minHeight: pt(BAND), slot: { elements: [
    block('field', 0, { backgroundColor: col('accent') }), // the name reversed out of it
    block('frame', 3.5, { borderColor: col('paper'), borderWidth: pt(0.75) }),
    text('name', '{title}', KAI, 700, 64, 'paper', { lineHeight: 1, letterSpacing: pt(6),
      placement: at(22, 13) }),
    text('kicker', '{subtitle}', HEI, 700, 12, 'paper', { placement: at(24, 82) }),
    text('sources', '錄{author}', HEI, 400, 8.5, 'paper', { placement: at(150, 84) }),
    text('issue', '{attr.issue}', HEI, 700, 12, 'paper', { placement: at(330, 33) }), // the year
    text('edition', '{attr.edition}', HEI, 400, 8.5, 'paper', { placement: at(330, 84) }),
    text('sheet', '第{pageNumber}張', HEI, 700, 10, 'accent', { placement: at(HEIGHT - 58, 80),
      box: { backgroundColor: col('paper'), padding: { top: pt(3), right: pt(3),
        bottom: pt(3), left: pt(3) } } }),
    // The headline down both tiers, centred; the dateline heads the deck's line.
    text('head', '{titleText}', SONG, 900, 44, 'ink', { align: 'center', lineHeight: 1.1,
      placement: at(0, MAST + 12, fill) }),
    text('deck', '{attr.deck}', KAI, 400, 15, 'ink', { align: 'center',
      placement: below('head', 6, fill) }),
    text('dateline', '{attr.dateline}', HEI, 700, 9, 'muted', { placement: below('head', 10) }),
    { kind: 'rule', id: 'foot', direction: 'horizontal', thickness: pt(0.75),
      color: col('ink'), placement: at(0, BAND - 3, fill) },
] } };
// #endregion

// #region heads: each story opens with a hairline, the headline, a deck and a dateline
const storyHead = { enabled: true, minHeight: pt(4 * LEAD), slot: { elements: [ // 4 lines
  { kind: 'rule', id: 'rule', direction: 'horizontal', thickness: pt(0.5), color: col('rule'),
    placement: at(0, 0, fill) },
  text('head', '{titleText}', SONG, 900, 20, 'ink', { placement: at(0, 6) }),
  text('deck', '{attr.deck}', KAI, 400, 11, 'ink', { // two characters down the tier
    placement: below('head', 4, { offset: { x: pt(2 * BODY), y: pt(4) } }) }),
  text('dateline', '{attr.dateline}', HEI, 700, 9, 'muted', { placement: below('deck', 4) }),
] } };
// #endregion

// #region pagehead: the second sheet's head and the colophon, horizontal on the sheet
// The header's frame is the margin above the tiers; the footer's, the margin below them.
const above = (y, extra = {}) => ({ anchor: { to: 'container', edge: 'top-left' },
  offset: { x: pt(0), y: mm(HEAD - y) }, ...extra });
const header = { elements: [
  text('title', '{title}', KAI, 700, 14, 'ink', { align: 'right', placement: above(13, fill) }),
  text('sheet', '第{pageNumber}張', HEI, 700, 9, 'ink', { placement: above(10.8) }),
  { kind: 'rule', id: 'rule', thickness: pt(1.5), color: col('ink'), placement: above(6, fill) },
].map((element) => ({ ...element, pages: 'body' })) }; // page 1 has the masthead instead
const footer = { elements: [text('colophon', '{attr.colophon}', HEI, 400, 7, 'muted', {
  pages: 'body', placement: at(0, 17, fill) })] }; // 6 mm under the tiers
// #endregion

const config = () => ({ // a factory: the engine caches resolved configs per object
  locale: 'zh-Hant', // Taiwan conventions: centred punctuation (gotcha: cjk-locale-tag)
  colorPalette,
  page: {
    sizePreset: 'custom', width: mm(TRIM.w), height: mm(TRIM.h), dpi: 150,
    backgroundColor: col('paper'),
    margins: { top: mm(MARGIN.top), bottom: mm(MARGIN.bottom), left: mm(MARGIN.side),
      right: mm(MARGIN.side), mirror: true },
    pageNumbering: { format: 'trad-chinese-informal' }, // 第一張, 第二張
  },
  layout,
  cjk,
  bodyText: {
    fontFamily: SONG, fontSize: pt(BODY), lineHeight: pt(LEAD), color: col('ink'),
    boldColor: col('ink'), italicColor: col('ink'), referenceColor: col('ink'),
    textAlign: 'justify', firstLineIndent: em(2), indentAfterHeading: true,
  },
  headings: {
    fontFamily: SONG, fontWeight: 900, color: col('ink'),
    levels: [
      // Restated: any headings object drops the H1 break (gotcha: headings-drop-h1-break).
      { level: 1, span: 'page', breakBefore: { enabled: true, parity: 'any' },
        marginBottom: pt(0) },
      { level: 2, fontSize: pt(20), lineHeight: pt(2 * LEAD), marginTop: pt(LEAD / 2),
        marginBottom: pt(0), advancedDesign: storyHead },
    ],
  },
  headingStyles: [{ id: 'front', advancedDesign: front }],
  calloutStyles: [wires],
  paragraphStyles: [
    { id: 'source', fontFamily: HEI, fontSize: pt(8.5), color: col('muted'), textAlign: 'right',
      firstLineIndent: pt(0) }, // the telegrams' source, at the foot of its line
    { id: 'inscription', fontFamily: KAI, indent: em(2), firstLineIndent: em(2) }, // 低二格
  ],
  header,
  footer,
});

// ─── 2 · Content ────────────────────────────────────────────────────────────
const markdown = String.raw`---
Markdown sample · 48 lines · content.en.md
title: "民元舊聞"
subtitle: "民國元年報章選錄"
author: "上海《申報》及《臨時政府公報》"
---

# 西湖公宴孫中山紀事 {style="front" deck="孫君演說錢幣革命　陳其美誤會起立質問" dateline="杭州　《申報》十二月十一日" issue="中華民國元年　歲次壬子" edition="今日出紙兩張" colophon="Set in Noto Serif TC, Noto Sans TC and LXGW WenKai TC (SIL OFL) · Text: zh.wikisource, rev. 9458640 and 2490036 (CC BY-SA 4.0)"}

孫中山先生於本月八號蒞杭情形，已紀昨報。茲悉九號上午九時，孫先生命駕出城，致祭光復諸先烈，順道游覽三潭印月諸名勝。十句半鐘蒞公園，當由朱都督陪侍招待，並介紹軍政各界領袖行相見禮。十一句四十分，入席公宴。

入席後，經孫君首先演說，其宗旨注重整理財政，發達工商，而以錢幣革命為入手辦法。演畢，復經隨員前滬軍都督陳其美引申其辭；次朱都督表明贊同孫君政策；次第六師長呂公望演說，合國民全力扶持中央，群策群力，以固疆隅。詎陳其美誤會為一人布政，必令全國人民服從，起立質問。經講武堂長童伯吹諸君說明呂師長立言大意，以資駁復，陳即起立道歉而罷。

讌畢，由都督陪侍孫君合攝一影，並參觀藏書樓各機關。至五句鐘，排隊入城，赴國民公所團體宴會。並定十號晨赴江干察看路線，即在之江大學午餐；午後乘江墅車赴拱埠參觀商場；十一號出遊天竺、靈隱諸名勝；十三號專車回滬云。

## 浙都督追祭攻寧陣亡將士 {deck="斷橋沿堤盡懸五色旗　湖中船隻均懸白旗" dateline="杭州　《申報》十二月四日"}

浙江朱都督於十二月二號在西湖新公園追祭攻寧陣亡將士。天甫黎明，各軍隊已紛紛排隊前往錢塘門外，沿途均懸五色旗；至斷橋，則五色大旗及十八星白旛沿堤皆是。傾城人士絡繹於途，湖中船隻均懸追祭白旗一面。

十一時祭台招魂開祭，由楊雪門君贊禮啟幕。朱都督就主祭位，呂師長、屈民政司、張財政司、沈教育司、朱提法司（請孫君代表）以及旅長、團長、杭縣汪知事、省會警察局張雨蕉等均就陪祭位。旋由呂師長公望出席演說：「今日追祭諸先烈的榮耀，都是從去年戰死中來的。現在俄庫密約，正是我們國兒立功的時候。」勸勵現在將士一番，隨宣布浙軍攻寧戰況情形，並報告陣亡將士姓名、籍貫、人數。即上香、獻酌、獻帛，由魏在田諸君次第讀都督暨呂師長等祭文，全場行禮，奏樂退位。

午後各學校、各團體、各軍隊致祭。禮畢，由都督領首，全場追祭人員均至孤山忠墳行禮，將所佩之花均散於墳上而回。西賓亦有數人在場觀禮。馨香俎豆，諸烈為不朽矣。

:::callout{type="wires" span="page" placement="bottom" title="電報"}
:::columns{count=3}
**南京去電**　津浦路站電局速送廣東北伐軍司令姚雨平、協統林震鑒：聞我軍昨夜得勝，追敵數十里，足見士卒用命。深堪嘉許。總統孫文。勘。

**南京去電**　四川資州軍政府署鑒：劉光漢被拘，希派人護送來寧，勿苛待。總統府。宥。

**南京去電**　上海陳都督其美鑒：趙珊林為吾黨舊同志，去歲新軍反正之役，頗為出力。今聞因事繫獄，請念前功，即予省釋。孫文。宥。

**武昌來電**　南京孫大總統、上海伍外交總長鑒：停戰期限將滿，和議尚未告成。聞滿清已簡放張勳為南京總督，揆此情形，顯係滿清不願意共和，徒廢時期，以疲我軍士。此停戰期滿，彼方若不決定退位，共同組織共和民國，再議展期，決不承認。曲實在彼，即前次所提待遇從優之條件，一律取銷。鄂中全體軍士均已預備作戰，誓不願與滿清共和，再不可聽其狡展，致遏我軍義勇之氣。請大總統、外交總長將種種情形通告各國是幸。元洪。廿六號。
:::

:::paragraphs{style="source"}
以上錄《臨時政府公報》第一號，一月二十九日
:::
:::

## 湯蟄仙之紀功碑 {deck="仿法國凱旋門例　西湖公園之麓建凱旋碑" dateline="杭州　《申報》七月十七日"}

浙軍光復南京，功勳卓著，天保城一役戰績尤多。此次凱旋回杭，浙中父老除開會歡迎外，復仿法國凱旋門例，在西湖公園之麓建築凱旋碑，以誌不朽。適前都督湯蟄仙氏歸自海外，撰作序銘，刊於碑陰。豐功大文，誠足並垂百世也。原文錄下：

:::paragraphs{style="inscription"}
當武漢首義，江寧未附，浙與蘇、鎮、滬諸軍約從會攻，始收其地，建臨時政府。其後乃有媾和之議。方是時，緣江諸鎮新復，漢陽復陷，金陵扼塞東南，危所繫，一不舉則亂猶未撥。故共和之業，基於武昌，成於江寧，卒乃定於統一。數月之間，易號改朔，伊古以來未有也。而論者以謂江寧之役，蓋浙軍勞尤多云。

時壽潛承乏於浙，以今之第五軍軍長朱君瑞率師與諸軍會。朱君果立功，名顯榮於時。中華民國元年五月，悉所部八千人還。今浙江都督蔣君尊簋命參謀副長夏君超度地為壇，大集諸將，飲至獻捷，勞軍行賞。有司、羣僚、耆老、諸生、商賈、百工，各以其屬齎牛酒致頌，來觀禮者至萬人，歌呼駿奔，闐衢溢巷，號曰歡迎凱旋，斯不亦盛哉！因伐石刊辭，將耀來葉，而以文請。壽潛既退在閭里，謹述邦人之意，為銘曰：

昭洪捷兮奠南疆，一禹域兮除穢荒。矯多士兮莫不揚，思禦侮兮在四方。樹隆碣兮示弗忘。
:::
`; // content.<lang>.md: the same Chinese text in both

// ─── 3 · Fonts ──────────────────────────────────────────────────────────────
// Every face the pages paint; the Chinese ones by files (gotcha: cjk-fonts-slices).
const FONTS = { 'Noto Serif TC': ['400', '700', '900'], 'Noto Sans TC': ['400', '700'],
  'LXGW WenKai TC': ['400', '700'] };
// #region voices: each face loads the files of the text it sets
const pick = (pattern) => (markdown.match(pattern) ?? []).join('');
const attrs = (...keys) => pick(new RegExp(`[{ ](?:${keys.join('|')})="[^"]*"`, 'g'));
const voices = [ // family, weights, the text it sets, and whether it runs down a column
  [SONG, ['400'], markdown, true], // the text
  [SONG, ['700', '900'], pick(/^#+ [^{\n]*|\*\*[^*]+\*\*/gm), false], // heads, labels
  [HEI, ['400', '700'], pick(/^(?:subtitle|author): .*$|style="source"\}[^:]*/gm) // masthead,
    + attrs('dateline', 'issue', 'edition', 'title', 'colophon') + '錄第一二張', true], // datelines
  [KAI, ['400'], attrs('deck') + pick(/style="inscription"\}[^:]*/g), true], // decks, the stele
  [KAI, ['700'], pick(/^title: .*$/m), false], // the paper's name
];
// #endregion

// ─── 4 · Build & show ───────────────────────────────────────────────────────
await loadFonts(FONTS, markdown);
for (const [family, weights, text, vertical] of voices) {
  await loadCjkFonts({ [family]: weights }, text, { vertical });
}
const doc = await buildWithFonts(() => buildDocument({ markdown }, config()), markdown);
showBook(doc, { title: t({ en: 'A vertical newspaper page in tiers',
  es: 'Una página de periódico vertical, en pisos' }) });
offerPdf(() => renderToPdf(doc, { fontProvider: cjkPdfProvider }), `${RECIPE}.pdf`);

Kit · core, fonts, viewer, pdf, cjk: the same in every recipe · 422 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 · 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 goes to fontsourceProvider (the "pdf" block). */
async function cjkPdfProvider(family, weight, style, request) {
  if (!(await isCjkFamily(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 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()));
  }));
}

/** 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 ───────────────────────────────────────────────────────────────────────