如何使用云函数制作缩略图并将其放置在Firebase存储中的特定文件夹中？

const functions = require('firebase-functions');
const admin = require('firebase-admin');
const { Storage } = require('@google-cloud/storage');
const sharp = require('sharp');

admin.initializeApp();

exports.generateThumbnail = functions.storage.object().onFinalize(async (object) => {
  const bucket = admin.storage().bucket(object.bucket);
  const filePath = object.name;
  const fileName = filePath.split('/').pop();
  const bucketDir = 'thumbnails';

  if (fileName.startsWith('thumb_')) {
    console.log('Already a thumbnail');
    return null;
  }

  const workingDir = '/tmp';
  const tempFilePath = `${workingDir}/${fileName}`;

  await bucket.file(filePath).download({
    destination: tempFilePath,
  });

  const thumbFileName = `thumb_${fileName}`;
  const thumbFilePath = `${workingDir}/${thumbFileName}`;
  const thumbFileBucket = bucket.file(`${bucketDir}/${thumbFileName}`);

  await sharp(tempFilePath)
    .resize(200, 200)
    .toFile(thumbFilePath);

  await bucket.upload(thumbFilePath, {
    destination: thumbFileBucket,
  });

  return thumbFileBucket.makePublic();
});