#2 Resolving Server Side Multer diskStorage destination errors on production environment (vercel)

//Previous Code with Error

//multerConfig.js
const multer = require('multer');
// Set up Multer for file upload
const storage = multer.diskStorage({
  destination: (req, file, cb) => {
    cb(null, 'uploads/'); // Directory to save uploaded files
  },
  filename: (req, file, cb) => {
    cb(null, `${file.originalname}`); // File naming convention
  },
});
const uploads = multer({ storage });
module.exports = uploads;
//Profile Upload Route
// In your routes file
router.post('/profile/profile_upload', uploads.single('photo'), profile_upload);
//photo is the key or fieldname from the client-side
//Profile Upload Function
const profile_upload = asyncHandler(async (req, res) => {
  try {
    const filePath = req.file.path;
    const userId = req.user._id;

    // Upload the image to Cloudinary with user ID as part of the public ID or metadata
    const uploadResult = await cloudinary.v2.uploader.upload(filePath, {
      asset_folder: 'upload_profile',
      resource_type: 'image',
      public_id: `${userId}`,
    });

    // Clean up the uploaded file from the server
    fs.unlinkSync(filePath);

    const profile_image = {
      public_id: uploadResult.public_id,
      url: uploadResult.secure_url
    };

    const userImage = await UserImage.create({
      user_id: userId,
      profile_image
    });

    res.status(201).json(userImage);
  } catch (error) {
    console.error(error);
    res.status(500).send('Failed to upload image.');
  }
});

//Solution to the Problem

// multerConfig.js
const multer = require('multer');
const storage = multer.memoryStorage();
const uploads = multer({ storage });
module.exports = uploads;
//Updated Profile Upload Function
const profile_upload = asyncHandler(async (req, res) => {
  try {
    const file = req.file;
    const userId = req.user._id;

    if (!file) {
      return res.status(400).send('No file uploaded.');
    }

    // Upload the file buffer directly to Cloudinary
    const uploadResult = await new Promise((resolve, reject) => {
      const uploadStream = cloudinary.v2.uploader.upload_stream({
        asset_folder: 'upload_profile',   // Optional: specify a folder for the image
        resource_type: 'image',
        public_id: `${userId}`,     // Set the public_id for the image
      }, (error, result) => {
        if (error) {
          reject(error);
        } else {
          resolve(result);
        }
      });

      // Write the buffer to the stream
      uploadStream.end(file.buffer);
    });

    const profile_image = {
      public_id: uploadResult.public_id,
      url: uploadResult.secure_url
    };

    const userImage = await UserImage.create({
      user_id: userId,
      profile_image
    });

    res.status(201).json(userImage);
  } catch (error) {
    console.error(error);
    res.status(500).send('Failed to upload image.');
  }
});