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* Purge unused CSS from the production build.
*
* Scans every `dist/**\/*.html` page (which already includes the ~3 500
* generated news articles, dashboards, sitemaps and political-intelligence
* pages emitted by `vite-plugin-static-pages.js`), all first-party JS
* bundled into `dist/` **and** the source trees `js/` + `src/browser/`,
* then rewrites each stylesheet shipped to S3 in-place — keeping only the
* selectors that those pages or their runtime JS reference.
*
* The source-tree scan is intentional: Vite tree-shakes / mangles class
* strings during bundling, so a class that only appears in `src/browser`
* source might not survive in the emitted JS even though the runtime
* still toggles it (e.g. via `classList.add('hidden')`). Including the
* unminified sources is a safety net against accidentally purging those
* runtime-toggled classes; it is the right trade-off for a static-site
* pipeline where the source corpus is small relative to the dist tree.
*
* Targets:
* - `dist/styles.css` (legacy non-hashed root copy that
* `scripts/deploy-s3.sh` cache-busts on
* every push)
* - `dist/assets/styles-*.css` (Vite-hashed bundle linked from every
* modern page; the static-pages plugin
* rewrites the `<link href>` to it)
*
* Filenames are preserved (PurgeCSS only mutates contents) so all
* existing `<link>` hrefs and CloudFront URLs continue to work.
*
* The safelist captures classes/attributes that are added at runtime by
* the theme switcher (`data-theme="dark"` / `light`), the lazy-loaded
* dashboard / chart code, Mermaid diagrams (which inject `mermaid-*`
* SVGs only after JS executes), and the article-type selectors that may
* not appear in every sampled HTML file but are used by news articles
* not yet in the corpus when this script runs locally.
*
* @author Hack23 AB
* @license Apache-2.0
*/
import { promises as fs } from 'node:fs';
import path from 'node:path';
import process from 'node:process';
import { fileURLToPath } from 'node:url';
import { PurgeCSS } from 'purgecss';
const projectRoot = path.resolve(
path.dirname(fileURLToPath(import.meta.url)),
'..',
);
interface PurgeStat {
/** Stylesheet path relative to projectRoot. */
file: string;
/** Original byte size of the stylesheet on disk. */
before: number;
/** Byte size after PurgeCSS rewrite. */
after: number;
}
/**
* Recursively collect every file under `dir` whose basename matches one
* of the supplied extensions. Skips `node_modules`, `.git` and
* `.vite` directories so we never accidentally feed the purger huge
* vendor blobs.
*/
async function walk(
dir: string,
exts: ReadonlySet<string>,
out: string[] = [],
): Promise<string[]> {
let entries: import('node:fs').Dirent[];
try {
entries = await fs.readdir(dir, { withFileTypes: true });
} catch {
return out;
}
for (const entry of entries) {
const full = path.join(dir, entry.name);
if (entry.isDirectory()) {
Iif (
entry.name === 'node_modules' ||
entry.name === '.git' ||
entry.name === '.vite'
) {
continue;
}
await walk(full, exts, out);
} else if (exts.has(path.extname(entry.name).toLowerCase())) {
out.push(full);
}
}
return out;
}
/**
* Build the PurgeCSS safelist. Anything that is added to the DOM only
* after JavaScript runs (theme switcher, Mermaid SVG IDs, Chart.js
* tooltip nodes, lazy-loaded dashboard cards) MUST live here, otherwise
* the purger will drop the matching CSS rules and the live site will
* regress visually.
*/
function buildSafelist() {
return {
/* Selectors kept verbatim regardless of HTML scan */
standard: [
/^html$/,
/^body$/,
/:root/,
/^dark-mode$/,
/^light-mode$/,
/^theme-transition$/,
/^visible$/,
/^hidden$/,
/^loading$/,
/^error$/,
/^block$/,
/^none$/,
/aria-/,
],
/* Pattern-matched selectors (and any descendants) preserved */
deep: [
/^mermaid/i,
/^chartjs/i,
/^chart-/i,
/^hljs/i, // syntax highlighting on news articles
/article-type-/,
/data-theme/,
/^dashboard-/,
/^cia-/,
/^cyberpunk/,
/^swot/,
/^mindmap/,
/^reader-guide/,
],
/* Greedy: keep entire selector chain if any token matches */
greedy: [/article-type-/, /data-theme/],
/* CSS custom properties — `variables: false` below disables PurgeCSS
* variable removal entirely; this entry is a defensive safety net in
* case that flag is ever flipped on. */
variables: [/--/],
/* @keyframes — `keyframes: false` below disables removal entirely;
* this entry is a defensive safety net for the same reason. */
keyframes: [/.*/],
};
}
/**
* Options for {@link purge}.
*/
interface PurgeOptions {
/**
* When `true` (default, production behaviour), also scan the
* `js/` and `src/browser/` source trees in addition to the `dist/`
* output. This is the safety net described in the module header
* against tree-shaking eliminating runtime-toggled class strings.
*
* Tests against in-tree fixtures should pass `false` so the test
* stays decoupled from the main repo source corpus and remains
* deterministic if unrelated source files change.
*/
scanSourceTree?: boolean;
}
async function purge(
distDir: string,
options: PurgeOptions = {},
): Promise<PurgeStat[]> {
const { scanSourceTree = true } = options;
const htmlExts: ReadonlySet<string> = new Set(['.html']);
const jsExts: ReadonlySet<string> = new Set(['.js', '.mjs']);
const cssExts: ReadonlySet<string> = new Set(['.css']);
/* Collect content sources from the built output (HTML + emitted JS).
* Adding the source `js/` and `src/browser/` directories captures any
* class strings that survive minification but were rewritten in the
* built bundles. Tests opt out via `scanSourceTree: false` so the
* fixture is the only content corpus considered. */
const htmlFiles = await walk(distDir, htmlExts);
const jsFiles = await walk(distDir, jsExts);
const srcJs = scanSourceTree
? await walk(path.join(projectRoot, 'js'), jsExts)
: [];
const srcTs = scanSourceTree
? await walk(path.join(projectRoot, 'src', 'browser'), new Set(['.ts']))
: [];
if (htmlFiles.length === 0) {
throw new Error(
`[purge-css] No HTML files found under ${distDir}. ` +
`Run \`npm run build\` first.`,
);
}
/* Stylesheets to purge. We only purge the two targets actually
* shipped to S3: the legacy root `dist/styles.css` and the Vite-hashed
* `dist/assets/styles-*.css`. Component sub-stylesheets are inlined
* into one of those by Vite's CSS bundler, so they don't need a
* separate pass. */
const cssCandidates = await walk(distDir, cssExts);
const cssTargets = cssCandidates.filter((file) => {
const rel = path.relative(distDir, file);
return (
rel === 'styles.css' ||
/^assets[/\\]styles-[A-Za-z0-9_-]+\.css$/.test(rel)
);
});
if (cssTargets.length === 0) {
throw new Error(
`[purge-css] No styles.css targets found under ${distDir}. ` +
`Expected dist/styles.css or dist/assets/styles-*.css.`,
);
}
const safelist = buildSafelist();
const stats: PurgeStat[] = [];
/* PurgeCSS returns one result per `css` entry, in order, so we run
* one pass per stylesheet to get accurate per-file size deltas and
* to avoid cross-contamination if Vite ever emits more than one. */
for (const cssPath of cssTargets) {
const before = (await fs.stat(cssPath)).size;
const result = await new PurgeCSS().purge({
content: [...htmlFiles, ...jsFiles, ...srcJs, ...srcTs],
css: [cssPath],
safelist,
defaultExtractor: (content) =>
content.match(/[A-Za-z0-9_-]+/g) ?? [],
keyframes: false, // do not attempt to remove unused @keyframes (Chart.js / Mermaid inject animation names at runtime)
fontFace: true, // remove unused @font-face
variables: false, // do not attempt to remove unused CSS variables (theme tokens are referenced from JS-set inline styles)
});
const purged = result[0]?.css ?? '';
await fs.writeFile(cssPath, purged, 'utf8');
const after = Buffer.byteLength(purged, 'utf8');
stats.push({
file: path.relative(projectRoot, cssPath),
before,
after,
});
}
return stats;
}
function fmtKb(bytes: number): string {
return `${(bytes / 1024).toFixed(1)} KiB`;
}
async function main(): Promise<void> {
const distArg = process.argv[2] ?? path.join(projectRoot, 'dist');
const distDir = path.resolve(distArg);
console.log(`🧹 Purging unused CSS in ${distDir}…`);
const stats = await purge(distDir);
for (const s of stats) {
const saved = s.before - s.after;
const pct = s.before > 0 ? ((saved / s.before) * 100).toFixed(1) : '0.0';
console.log(
` • ${s.file}: ${fmtKb(s.before)} → ${fmtKb(s.after)} ` +
`(saved ${fmtKb(saved)}, ${pct}%)`,
);
}
const totalBefore = stats.reduce((acc, s) => acc + s.before, 0);
const totalAfter = stats.reduce((acc, s) => acc + s.after, 0);
const totalSaved = totalBefore - totalAfter;
const totalPct =
totalBefore > 0 ? ((totalSaved / totalBefore) * 100).toFixed(1) : '0.0';
console.log(
`✅ Purge complete: ${fmtKb(totalBefore)} → ${fmtKb(totalAfter)} ` +
`(saved ${fmtKb(totalSaved)}, ${totalPct}%)`,
);
}
/* Allow `import { purge }` from tests without triggering the CLI. */
const isMain =
process.argv[1] !== undefined &&
path.resolve(process.argv[1]) === fileURLToPath(import.meta.url);
Iif (isMain) {
main().catch((err) => {
console.error('[purge-css]', err);
process.exit(1);
});
}
export { purge, buildSafelist };
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