#!/usr/bin/env node
/**
 * Build-time precompress for web/dist: write sibling .br / .gz variants.
 * Zero npm deps — uses Node zlib (available in node:22-bookworm web-builder).
 */
import fs from 'node:fs';
import path from 'node:path';
import { brotliCompressSync, constants as zlibConstants, gzipSync } from 'node:zlib';
import { fileURLToPath } from 'node:url';

const __dirname = path.dirname(fileURLToPath(import.meta.url));
const distDir = path.resolve(__dirname, '..', 'dist');
const MIN_BYTES = 1024;
const COMPRESS_EXT = new Set(['.js', '.css', '.html', '.svg', '.json', '.txt', '.xml', '.map']);
const SKIP_EXT = new Set(['.woff', '.woff2', '.png', '.jpg', '.jpeg', '.gif', '.webp', '.ico', '.br', '.gz']);

function walk(dir, out = []) {
  for (const ent of fs.readdirSync(dir, { withFileTypes: true })) {
    const full = path.join(dir, ent.name);
    if (ent.isDirectory()) walk(full, out);
    else out.push(full);
  }
  return out;
}

function shouldCompress(filePath) {
  const ext = path.extname(filePath).toLowerCase();
  if (SKIP_EXT.has(ext)) return false;
  if (!COMPRESS_EXT.has(ext)) return false;
  const st = fs.statSync(filePath);
  return st.size >= MIN_BYTES;
}

function writeIfSmaller(sourcePath, variantPath, buf, label, originalSize) {
  if (buf.length >= originalSize) {
    if (fs.existsSync(variantPath)) fs.unlinkSync(variantPath);
    return null;
  }
  fs.writeFileSync(variantPath, buf);
  const pct = ((1 - buf.length / originalSize) * 100).toFixed(1);
  console.log(
    `  ${label.padEnd(4)} ${path.relative(distDir, sourcePath)}  ${originalSize} → ${buf.length} (−${pct}%)`,
  );
  return buf.length;
}

if (!fs.existsSync(distDir)) {
  console.error(`precompress: missing ${distDir}; run vite build first`);
  process.exit(1);
}

const files = walk(distDir).filter(shouldCompress);
console.log(`precompress: ${files.length} candidate(s) under ${distDir}`);

let brCount = 0;
let gzCount = 0;
for (const file of files) {
  const raw = fs.readFileSync(file);
  const br = brotliCompressSync(raw, {
    params: {
      [zlibConstants.BROTLI_PARAM_QUALITY]: 11,
      [zlibConstants.BROTLI_PARAM_SIZE_HINT]: raw.length,
    },
  });
  const gz = gzipSync(raw, { level: 9 });
  if (writeIfSmaller(file, `${file}.br`, br, 'br', raw.length) != null) brCount += 1;
  if (writeIfSmaller(file, `${file}.gz`, gz, 'gzip', raw.length) != null) gzCount += 1;
}

console.log(`precompress: wrote ${brCount} .br and ${gzCount} .gz`);