/**

* Writes the GitHub Social Preview PNG that a maintainer uploads by hand.

*

* GitHub exposes no API for the social preview — not REST, not GraphQL — so

* this is as far as automation reaches. The PNG is committed so the exact

* bytes destined for the repository settings are reviewable in a diff, and so

* regenerating after a brand change produces a visible change rather than a

* silent one.

*

* Usage:

* node scripts/export-github-card.mjs

* node scripts/export-github-card.mjs --origin http://localhost:3000

*/

import { mkdir, writeFile } from 'node:fs/promises';

import { dirname, join } from 'node:path';

import { fileURLToPath } from 'node:url';

const REPO_ROOT = join(dirname(fileURLToPath(import.meta.url)), '..');

const OUTPUT = join(REPO_ROOT, 'docs', 'brand', 'github-social-preview.png');

const DEFAULT_ORIGIN = 'https://threadplane.ai';

/**

* GitHub's documented size. Kept in sync BY HAND with GITHUB_CARD_SIZE in

* apps/website/src/app/github-card/route.tsx — this is a .mjs script and

* cannot import from the Next app's TypeScript module graph. Change one,

* change the other.

*/

const EXPECTED = { width: 1280, height: 640 };

function parseOrigin(argv) {

const at = argv.indexOf('--origin');

if (at === -1) return DEFAULT_ORIGIN;

const value = argv[at + 1];

if (value === undefined || value.startsWith('--')) {

console.error('--origin needs a value, e.g. --origin http://localhost:3000');

process.exit(1);

}

return value;

}

/**

* Reads width and height out of the PNG's IHDR chunk, which is always the

* first chunk: 8 bytes of signature, 4 of length, 4 of type, then the two

* big-endian 32-bit dimensions. Guards against committing a card the route

* silently resized, and against writing an HTML error page as a .png.

*/

function readPngSize(buffer) {

const isPng = buffer.subarray(0, 8).equals(Buffer.from([0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a]));

if (!isPng) return null;

return { width: buffer.readUInt32BE(16), height: buffer.readUInt32BE(20) };

}

const origin = parseOrigin(process.argv.slice(2));

const url = new url(/sitelet?url=https%3A%2F%2Fgithub.com%2Fcacheplane%2Fthreadplane%2Fblob%2Fmain%2Fscripts%2F%26%23039%3B%2Fgithub-card%26%23039%3B%2C%2520origin).toString();

// fetch resolves with a response object for HTTP-level failures (404, 500)

// but rejects outright when the connection itself never happens — no server

// listening, DNS failure, refused TLS. For a person running this by hand

// from a runbook, that is the single most likely failure (the dev server

// was never started, or the route is not deployed yet), so it gets the same

// one-line treatment as a non-ok response instead of a raw stack trace.

let response;

try {

response = await fetch(url);

} catch (cause) {

console.error(`Could not reach ${url}: ${cause.message}`);

process.exit(1);

}

if (!response.ok) {

console.error(`Failed to fetch ${url}: ${response.status} ${response.statusText}`);

process.exit(1);

}

const buffer = Buffer.from(await response.arrayBuffer());

const size = readPngSize(buffer);

if (!size) {

console.error(`${url} did not return a PNG. Got content-type: ${response.headers.get('content-type')}`);

process.exit(1);

}

if (size.width !== EXPECTED.width || size.height !== EXPECTED.height) {

console.error(

`${url} returned ${size.width}x${size.height}, expected ${EXPECTED.width}x${EXPECTED.height}.`,

);

process.exit(1);

}

await mkdir(dirname(OUTPUT), { recursive: true });

await writeFile(OUTPUT, buffer);

console.log(`Wrote ${OUTPUT} (${size.width}x${size.height}, ${buffer.length} bytes) from ${url}`);

console.log('');

console.log('GitHub has no API for this. Upload it by hand:');

console.log(' 1. https://github.com/cacheplane/threadplane/settings');

console.log(' 2. General -> Social preview -> Edit -> Upload an image');

console.log(' 3. Select docs/brand/github-social-preview.png');

console.log('');

console.log('Then confirm with:');

console.log(' curl -sL https://github.com/cacheplane/threadplane | grep \'og:image\"\'');

console.log('Expect a repository-images.githubusercontent.com URL, not opengraph.githubassets.com.');