/**
 * Fetches the app's font files into assets/fonts/.
 *
 * ── WHY THIS SCRIPT IS THE WAY IT IS ────────────────────────────────────────
 * The previous version pointed at `googlefonts/nunito/raw/main/fonts/ttf/`,
 * which no longer exists — that repo now ships variable fonts only. It also
 * piped whatever came back straight into the .ttf without looking at the HTTP
 * status. So running it after the URLs died wrote GitHub's 404 page into all
 * four font files, and every one of them was a 300KB HTML document with a
 * .ttf extension.
 *
 * Nothing complained. React Native does not validate a font asset: Android
 * silently falls back to Roboto, so the app rendered in the system font while
 * appearing to have a typeface of its own. That is the failure this script now
 * refuses to repeat:
 *
 *   - a non-2xx response aborts instead of being written to disk;
 *   - every download is checked for the TrueType magic number (0x00010000)
 *     before it is kept;
 *   - a file that fails either check is deleted, and the script exits non-zero.
 *
 * ── WHY THE FILENAMES LOOK ODD ──────────────────────────────────────────────
 * They are the fonts' own PostScript names, not IBM's file names. iOS resolves
 * `fontFamily` against the PostScript name while Android resolves it against
 * the asset filename, so the two only agree if the file is named after the
 * PostScript name. IBM abbreviates: SemiBold is `SmBld`, Medium is `Medm`, and
 * Regular has no suffix at all. Renaming them here is what lets
 * `fontFamily: 'IBMPlexSans-SmBld'` work on both platforms.
 *
 * After running this, re-link and rebuild — the files have to be inside the
 * binary, so a Metro reload alone will not pick them up:
 *
 *   node download-fonts.js
 *   npx react-native-asset
 *   npx react-native run-android
 */

/* eslint-disable no-undef -- A Node build script, not app code: the project's
   ESLint environment is React Native and does not declare Node globals. */

const fs = require('fs');
const https = require('https');
const path = require('path');

const PLEX = 'https://raw.githubusercontent.com/IBM/plex/master/packages';

/** `as` is the PostScript name — see the note above on why that is the filename. */
const fonts = [
  { as: 'IBMPlexSans.ttf', url: `${PLEX}/plex-sans/fonts/complete/ttf/IBMPlexSans-Regular.ttf` },
  { as: 'IBMPlexSans-Medm.ttf', url: `${PLEX}/plex-sans/fonts/complete/ttf/IBMPlexSans-Medium.ttf` },
  { as: 'IBMPlexSans-SmBld.ttf', url: `${PLEX}/plex-sans/fonts/complete/ttf/IBMPlexSans-SemiBold.ttf` },
  { as: 'IBMPlexSans-Bold.ttf', url: `${PLEX}/plex-sans/fonts/complete/ttf/IBMPlexSans-Bold.ttf` },
  { as: 'IBMPlexMono.ttf', url: `${PLEX}/plex-mono/fonts/complete/ttf/IBMPlexMono-Regular.ttf` },
  { as: 'IBMPlexMono-SmBld.ttf', url: `${PLEX}/plex-mono/fonts/complete/ttf/IBMPlexMono-SemiBold.ttf` },
];

const dir = path.join(__dirname, 'assets', 'fonts');

if (!fs.existsSync(dir)) {
  fs.mkdirSync(dir, { recursive: true });
}

/** Buffers the body so nothing reaches disk until the status has been checked. */
const fetch = (url, redirects = 0) =>
  new Promise((resolve, reject) => {
    if (redirects > 5) {
      reject(new Error('too many redirects'));
      return;
    }

    https
      .get(url, (response) => {
        const { statusCode, headers } = response;

        if (statusCode === 301 || statusCode === 302 || statusCode === 307 || statusCode === 308) {
          response.resume();
          fetch(headers.location, redirects + 1).then(resolve, reject);
          return;
        }

        if (statusCode !== 200) {
          response.resume();
          reject(new Error(`HTTP ${statusCode}`));
          return;
        }

        const chunks = [];
        response.on('data', (chunk) => chunks.push(chunk));
        response.on('end', () => resolve(Buffer.concat(chunks)));
        response.on('error', reject);
      })
      .on('error', reject);
  });

/**
 * A TrueType file opens with sfntVersion 0x00010000. `OTTO` would be an
 * OpenType/CFF font, which React Native on Android will not load, and anything
 * else — an HTML error page, most likely — is not a font at all.
 */
const isTrueType = (buffer) => buffer.length > 4 && buffer.readUInt32BE(0) === 0x00010000;

const run = async () => {
  let failed = 0;

  for (const font of fonts) {
    const dest = path.join(dir, font.as);

    try {
      const body = await fetch(font.url);

      if (!isTrueType(body)) {
        const magic = body.length > 4 ? body.readUInt32BE(0).toString(16) : 'empty';
        throw new Error(`not a TrueType file (magic 0x${magic}, ${body.length} bytes)`);
      }

      fs.writeFileSync(dest, body);
      console.log(`  ok       ${font.as}  (${body.length} bytes)`);
    } catch (error) {
      failed += 1;
      // Leave nothing half-written behind: a stale or truncated file here is
      // exactly what caused the silent fallback this script exists to prevent.
      fs.rmSync(dest, { force: true });
      console.error(`  FAILED   ${font.as}  — ${error.message}`);
    }
  }

  if (failed > 0) {
    console.error(`\n${failed} font(s) could not be fetched. Do not build with fonts missing.`);
    process.exitCode = 1;
    return;
  }

  console.log('\nAll fonts downloaded and verified.');
  console.log('Next: npx react-native-asset  &&  npx react-native run-android');
};

void run();