Jyotisha/frontend/tests/font-stack-loadable-contract.test.ts

import { existsSync, readFileSync } from "node:fs";
import assert from "node:assert/strict";
import test from "node:test";

/**
 * BUG-737: `--font-display` led with "Tiempos Headline" and `--font-body` with
 * StyreneB. Both are Anthropic licensed faces this app has never loaded — no
 * @font-face, nothing in public/, and layout.tsx vendors only Inter — so every
 * CJK heading fell through to the next entry, Songti SC / SimSun, for the life
 * of the product. Nothing failed, because nothing checked that a declared family
 * can actually resolve.
 *
 * This contract closes that: every quoted family in the two stacks must either
 * be vendored through next/font/local, be declared by a self-hosted @font-face
 * whose files exist (the heading face "Jyotisha Serif SC",
 * src/app/fonts/serif-sc/serif-sc.css), or be a face the OS is known to ship.
 *
 * 2026-09-28 (TASK-serif-headings-20260928): headings take a self-hosted serif.
 * BUG-737's conclusion "CJK never takes a serif" was overturned by product; its
 * two guards stay: a declared family must load, and a heading must never fall
 * through to a system 宋体 (Songti / STSong / SimSun / generic serif).
 */

const css = readFileSync(new URL("../src/app/globals.css", import.meta.url), "utf8");
const layout = readFileSync(new URL("../src/app/layout.tsx", import.meta.url), "utf8");

/** Faces that ship with a target OS, so naming them costs no request. */
const SYSTEM_FACES = new Set([
  // Apple
  "PingFang SC",
  "Helvetica Neue",
  // Windows
  "Microsoft YaHei",
  "Segoe UI",
  // Cross-platform fallbacks that are generic families or UA keywords.
  "Georgia",
  "Consolas",
  "SFMono-Regular",
  "JetBrains Mono",
]);

function stackValue(token: string): string {
  const match = css.match(new RegExp(`^\\s*${token}:\\s*([^;]+);`, "m"));
  assert.ok(match, `${token} must be declared in globals.css`);
  return match![1];
}

function quotedFamilies(stack: string): string[] {
  return [...stack.matchAll(/"([^"]+)"/g)].map((m) => m[1]);
}

const serifCssUrl = new URL("../src/app/fonts/serif-sc/serif-sc.css", import.meta.url);
const serifCss = readFileSync(serifCssUrl, "utf8");

/** Families declared by the self-hosted @font-face list whose every src file exists. */
function selfHostedFamilies(): Set<string> {
  const families = new Set<string>();
  for (const face of serifCss.matchAll(/@font-face\s*\{([^}]*)\}/g)) {
    const family = face[1].match(/font-family:\s*"([^"]+)"/)?.[1];
    const sources = [...face[1].matchAll(/url\("([^"]+)"\)/g)].map((m) => m[1]);
    assert.ok(family && sources.length > 0, "every @font-face in serif-sc.css names a family and a url()");
    for (const source of sources) {
      assert.ok(existsSync(new URL(source, serifCssUrl)), `${source} is declared in serif-sc.css but missing`);
    }
    families.add(family!);
  }
  return families;
}

/** Families vendored via next/font/local, keyed by the CSS variable they expose. */
function vendoredVariables(): string[] {
  return [...layout.matchAll(/variable:\s*"(--[a-z0-9-]+)"/g)].map((m) => m[1]);
}

test("every quoted family in the UI font stacks is either vendored or a system face", () => {
  // 原值：带引号的 family 只能属于 SYSTEM_FACES（next/font/local 的 Inter 以 var() 出现，不带引号）
  // 新值：也可以是 serif-sc.css 里 @font-face 声明过、且 url() 文件都存在的 family
  // 原因：TASK-serif-headings-20260928 标题改用自托管宋体；「声明的 family 必须真能加载」这半条原样保留，
  //       只是把「可加载」扩展到自托管 @font-face。
  const selfHosted = selfHostedFamilies();
  for (const token of ["--font-display", "--font-body"]) {
    const stack = stackValue(token);
    for (const family of quotedFamilies(stack)) {
      assert.ok(
        SYSTEM_FACES.has(family) || selfHosted.has(family),
        `${token} names "${family}", which is neither vendored (next/font/local or serif-sc.css) nor a known system face. `
          + "A family that cannot load is dead configuration: it makes the stack look intentional while the "
          + "browser silently falls through to the next entry. Vendor it into src/app/fonts/ with an OFL/SIL "
          + "licence file beside it, or drop the name. See BUG-737.",
      );
    }
  }
});

test("the UI font stacks resolve through the vendored Inter variable", () => {
  const vendored = vendoredVariables();
  assert.ok(vendored.includes("--font-inter"), "layout.tsx must vendor Inter through next/font/local");
  for (const token of ["--font-display", "--font-body"]) {
    assert.match(
      stackValue(token),
      /var\(--font-inter, Inter\)/,
      `${token} must route through the vendored Inter variable rather than naming a face it cannot load`,
    );
  }
});

// 原值：test("no CJK serif is reachable from the display stack")——栈里不得有 Songti / STSong / SimSun /
//       Noto Serif / Source Han Serif，也不得以通用 serif 结尾（BUG-737：CJK 不用衬线）。
// 新值：--font-display 第一个 family 是自托管的 "Jyotisha Serif SC"；系统宋体与通用 serif 仍然禁止。
// 原因：TASK-serif-headings-20260928 决策 1 推翻「CJK 不用衬线」，但「不得落到系统宋体」保留：
//       自托管切片没到或字不在收录范围时，标题退回无衬线，不退回 SimSun。
test("the display stack leads with the self-hosted serif and never reaches a system 宋体", () => {
  const display = stackValue("--font-display");
  assert.equal(quotedFamilies(display)[0], "Jyotisha Serif SC", "--font-display must lead with the self-hosted heading face");
  assert.match(display.trim(), /^"Jyotisha Serif SC",/);
  for (const banned of ["Songti", "STSong", "SimSun", "Noto Serif CJK SC", "Noto Serif SC", "Source Han Serif"]) {
    assert.doesNotMatch(
      display,
      new RegExp(banned.replace(/ /g, "\\s")),
      `--font-display must not reach "${banned}": a system 宋体 is exactly BUG-737 (SimSun on Windows)`,
    );
  }
  // The generic `serif` keyword too — but not the `sans-serif` it is a suffix of.
  assert.doesNotMatch(
    display,
    /(^|[\s,])serif\b/,
    "--font-display must not end in the generic serif family; the UA default for CJK there is 宋体",
  );
  assert.match(display.trim(), /sans-serif$/, "an unloaded slice falls back to sans, not to a system serif");
  assert.equal(
    display.replace(/^"Jyotisha Serif SC",\s*/, ""),
    stackValue("--font-body"),
    "after the heading face, display falls through to exactly the body stack",
  );
});

test("display rank comes from weight, not from a second family", () => {
  // Written when display and body shared one sans stack (BUG-737). Headings now
  // lead with "Jyotisha Serif SC", but until a slice arrives (and for characters
  // outside its 6500) they still render in the body stack, so every display rule
  // keeps carrying its own weight. The self-hosted face only ships SemiBold,
  // declared as font-weight 500 700, so 500 and 600 both hit it.
  const displayRules = [...css.matchAll(/font-family:\s*var\(--font-display\)/g)];
  assert.ok(displayRules.length > 10, "sanity: the display token should still be in wide use");
  assert.doesNotMatch(
    css,
    /font-family:\s*var\(--font-display\);\s*font-size:[^;]*;\s*font-weight:\s*400\s*;/,
    "a --font-display rule still sits at weight 400; in the sans fallback that is body rank",
  );
});