import { readFile, writeFile } from 'node:fs/promises';
import { join } from 'node:path';
import { fileURLToPath } from 'node:url';

const ROOT = fileURLToPath(new URL('..', import.meta.url));
const AVATAR_DIRECTORY = join(ROOT, 'assets', 'chickpea-avatars', 'agent-defaults');
const OUTPUT = join(
  ROOT,
  'src',
  'slack',
  'agent-presence',
  'default-avatar-pool.generated.ts',
);
const PNG_SIGNATURE = Buffer.from([137, 80, 78, 71, 13, 10, 26, 10]);
const AVATAR_FILES = [
  '01-sage.png',
  '02-coral.png',
  '03-lilac.png',
  '04-mineral-blue.png',
  '05-dusty-rose.png',
  '06-deep-moss.png',
  '07-periwinkle.png',
  '08-seafoam.png',
  '09-warm-oat.png',
  '10-midnight-indigo.png',
  '11-apricot.png',
  '12-muted-berry.png',
];

for (const file of AVATAR_FILES) {
  const bytes = await readFile(join(AVATAR_DIRECTORY, file));
  if (!bytes.subarray(0, PNG_SIGNATURE.length).equals(PNG_SIGNATURE)) {
    throw new Error(`${file} is not a PNG`);
  }
  if (bytes.subarray(12, 16).toString('ascii') !== 'IHDR') {
    throw new Error(`${file} has no PNG IHDR`);
  }
  const width = bytes.readUInt32BE(16);
  const height = bytes.readUInt32BE(20);
  if (width !== 512 || height !== 512) {
    throw new Error(`${file} must be exactly 512x512, got ${width}x${height}`);
  }
  if (bytes.byteLength > 512 * 1_024) {
    throw new Error(`${file} exceeds Slack's 512 KiB avatar budget`);
  }
}

const source = `// Generated by scripts/build-agent-avatar-pool.mjs. Do not edit by hand.\n` +
  `export const DEFAULT_AGENT_AVATAR_FILES = ${JSON.stringify(AVATAR_FILES, null, 2)} as const;\n`;

await writeFile(OUTPUT, source);
console.log(`Wrote ${AVATAR_FILES.length} Agent avatars to ${OUTPUT}`);