transform-bunchee.mjs

import {
  copyFile,
  readFile,
  readdir,
  unlink,
  writeFile,
} from "node:fs/promises";
import { basename } from "node:path";

const CJS_DIR = new URL("./dist/cjs", import.meta.url).pathname;
const ESM_DIR = new URL("./dist/es", import.meta.url).pathname;

const stripComments = (content) => {
  return content.replace(/\/\*[\s\S]*?\*\/|\/\/.*/g, "").trim();
};

const isTypeScriptDefinition = (content) => {
  const stripped = stripComments(content);
  const tsDefinitionPattern =
    /declare\s+|export\s+interface|export\s+type|export\s+namespace|export\s+const|export\s+enum|export\s+function|export\s+class|export\s+abstract\s+class|export\s+var/;
  return tsDefinitionPattern.test(stripped);
};

async function renameFileExtension(path, extension) {
  const newPath = path.replace(/\.js$/, extension);
  await copyFile(path, newPath);
  // Delete old file
  await unlink(path);

  return newPath;
}

async function processFile(file, dir) {
  const path = `${dir}/${file}`;

  if (!file.endsWith(".js")) {
    return;
  }

  const content = await readFile(path, "utf8");

  if (!isTypeScriptDefinition(content)) {
    return;
  }

  // replace the .js extension with .d.mts or .d.ts if in cjs dir
  if (dir === CJS_DIR) {
    return await renameFileExtension(path, ".d.ts");
  } else {
    return await renameFileExtension(path, ".d.mts");
  }
}

async function transformDTS(files, dir) {
  const fileMap = new Map();
  for await (const file of files) {
    const path = await processFile(file, dir);

    if (!path) {
      // No match
      continue;
    }

    // We have a new file path, now we need to get the exact fileName and replace all import statements in all files
    const fileName = basename(path);
    fileMap.set(file, fileName);
  }

  // Loop through all files and replace import statements
  for (const filename of await readdir(dir)) {
    const path = `${dir}/${filename}`;

    for (const [old, newName] of Array.from(fileMap.entries())) {
      const content = await readFile(path, "utf8");
      const newContent = content.replaceAll(old, newName);

      if (newContent !== content) {
        await writeFile(path, newContent);
      }
    }
  }
}

await transformDTS(await readdir(CJS_DIR), CJS_DIR);
await transformDTS(await readdir(ESM_DIR), ESM_DIR);