import { readdir, readFile, writeFile } from 'node:fs/promises';
import { basename, extname, join, relative } from 'node:path';

const POSTS_DIR = join(process.cwd(), 'source', '_posts');

const CRC32_TABLE = new Uint32Array(256);

for (let i = 0; i < 256; i += 1) {
  let value = i;
  for (let bit = 0; bit < 8; bit += 1) {
    value = value & 1 ? 0xedb88320 ^ (value >>> 1) : value >>> 1;
  }
  CRC32_TABLE[i] = value >>> 0;
}

function crc32(input) {
  const bytes = new TextEncoder().encode(input);
  let crc = 0xffffffff;

  for (const byte of bytes) {
    crc = CRC32_TABLE[(crc ^ byte) & 0xff] ^ (crc >>> 8);
  }

  return ((crc ^ 0xffffffff) >>> 0).toString(16);
}

async function listMarkdownFiles(dir) {
  const entries = await readdir(dir, { withFileTypes: true });
  const files = await Promise.all(
    entries.map(async (entry) => {
      const path = join(dir, entry.name);
      if (entry.isDirectory()) return listMarkdownFiles(path);
      if (entry.isFile() && extname(entry.name).toLowerCase() === '.md') return [path];
      return [];
    }),
  );

  return files.flat();
}

function getFrontmatterBounds(content) {
  if (!content.startsWith('---')) return null;

  const newline = content.includes('\r\n') ? '\r\n' : '\n';
  const lines = content.split(newline);
  const closeIndex = lines.findIndex((line, index) => index > 0 && line.trim() === '---');

  if (closeIndex === -1) return null;
  return { closeIndex, lines, newline };
}

function getScalar(frontmatterLines, key) {
  const pattern = new RegExp(`^${key}\\s*:\\s*(.*)$`);
  const match = frontmatterLines.map((line) => line.match(pattern)).find(Boolean);
  if (!match) return '';

  return match[1]
    .trim()
    .replace(/^['"]|['"]$/g, '')
    .trim();
}

function makeSeed(file, frontmatterLines) {
  const title = getScalar(frontmatterLines, 'title');
  if (title) return title;

  const filename = getScalar(frontmatterLines, 'filename');
  if (filename) return filename;

  return basename(file, '.md');
}

function makeUniqueAbbrlink(seed, usedAbbrlinks) {
  let attempt = 0;
  let abbrlink = crc32(seed);

  while (usedAbbrlinks.has(abbrlink)) {
    attempt += 1;
    abbrlink = crc32(`${seed}:${attempt}`);
  }

  usedAbbrlinks.add(abbrlink);
  return abbrlink;
}

async function main() {
  const files = await listMarkdownFiles(POSTS_DIR);
  const usedAbbrlinks = new Set();
  const pending = [];

  for (const file of files) {
    const content = await readFile(file, 'utf8');
    const bounds = getFrontmatterBounds(content);
    if (!bounds) continue;

    const frontmatterLines = bounds.lines.slice(1, bounds.closeIndex);
    const existing = getScalar(frontmatterLines, 'abbrlink');

    if (existing) {
      usedAbbrlinks.add(existing);
      continue;
    }

    pending.push({ file, content, bounds, frontmatterLines });
  }

  for (const item of pending) {
    const seed = makeSeed(item.file, item.frontmatterLines);
    const abbrlink = makeUniqueAbbrlink(seed, usedAbbrlinks);
    const insertAt = item.bounds.closeIndex;

    item.bounds.lines.splice(insertAt, 0, `abbrlink: ${abbrlink}`);
    await writeFile(item.file, item.bounds.lines.join(item.bounds.newline), 'utf8');

    console.log(`Added abbrlink ${abbrlink} to ${relative(process.cwd(), item.file)}`);
  }

  if (pending.length === 0) {
    console.log('All posts already have abbrlink.');
  }
}

main().catch((error) => {
  console.error(error);
  process.exitCode = 1;
});