file-size.mjs

import { stat, readdir } from 'node:fs/promises';
import path from 'node:path';

import { BASE, HEAD, TITLE } from '../constants.mjs';

const UNITS = ['B', 'KB', 'MB', 'GB'];

/**
 * Formats bytes into human-readable format
 * @param {number} bytes - Number of bytes
 * @returns {string} Formatted string (e.g., "1.50 KB")
 */
const formatBytes = bytes => {
  if (!bytes) {
    return '0 B';
  }

  const i = Math.floor(Math.log(Math.abs(bytes)) / Math.log(1024));
  return `${(bytes / Math.pow(1024, i)).toFixed(2)} ${UNITS[i]}`;
};

/**
 * Gets all files in a directory with their sizes
 * @param {string} dir - Directory path to scan
 * @returns {Promise<Map<string, number>>} Map of filename to size in bytes
 */
const getStats = async dir => {
  const files = await readdir(dir);
  return new Map(
    await Promise.all(
      files.map(async f => [f, (await stat(path.join(dir, f))).size])
    )
  );
};

// Fetch stats for both directories in parallel
const [baseStats, headStats] = await Promise.all([BASE, HEAD].map(getStats));

const didChange = f =>
  baseStats.has(f) && headStats.has(f) && baseStats.get(f) !== headStats.get(f);

const toDiffObject = f => ({
  file: f,
  base: baseStats.get(f),
  head: headStats.get(f),
  diff: headStats.get(f) - baseStats.get(f),
});

// Find files that exist in both directories but have different sizes,
// then sort by absolute diff (largest changes first)
const changed = [...new Set([...baseStats.keys(), ...headStats.keys()])]
  .filter(didChange)
  .map(toDiffObject)
  .sort((a, b) => Math.abs(b.diff) - Math.abs(a.diff));

// Output markdown table if there are changes
if (changed.length) {
  const rows = changed.map(({ file, base, head, diff }) => {
    const sign = diff > 0 ? '+' : '';
    const percent = `${sign}${((diff / base) * 100).toFixed(2)}%`;
    const diffFormatted = `${sign}${formatBytes(diff)} (${percent})`;

    return `| \`${file}\` | ${formatBytes(base)} | ${formatBytes(head)} | ${diffFormatted} |`;
  });

  console.log(TITLE);
  console.log('| File | Base | Head | Diff |');
  console.log('|-|-|-|-|');
  console.log(rows.join('\n') + '\n');
}