Problem: Standardize File Storage Clients

15 min

Adapt different file storage systems to a shared upload/download interface.

Problem statement

Your backend uses two file storage systems:

A local file system client for development, which saves files directly on disk.
A mock S3 client in production, which uploads files to a cloud bucket.

Both expose similar functionality but with different method names and behaviors:

The local client uses save(file) and read(file).
The S3-like client uses uploadFile(file) and getFile(file).

This mismatch makes your file-handling code messy and repetitive. You need one consistent interface for both.

Goal

Implement a StorageAdapter class that wraps either client and exposes these two methods:

.upload(file)
.download(file)

Each method should internally call the appropriate function from the wrapped client and return its result.

Constraints

Do not modify the original clients.
The adapter must detect which client it’s wrapping.
The calling code should always use .upload() and .download().
No hardcoded conditionals like if (env === 'dev'); use method detection instead.

Sample output

The examples below illustrate what the output should look like:

Problem: Standardize File Storage Clients

15 min

Adapt different file storage systems to a shared upload/download interface.

Problem statement

Your backend uses two file storage systems:

A local file system client for development, which saves files directly on disk.
A mock S3 client in production, which uploads files to a cloud bucket.

Both expose similar functionality but with different method names and behaviors:

The local client uses save(file) and read(file).
The S3-like client uses uploadFile(file) and getFile(file).

This mismatch makes your file-handling code messy and repetitive. You need one consistent interface for both.

Goal

Implement a StorageAdapter class that wraps either client and exposes these two methods:

.upload(file)
.download(file)

Each method should internally call the appropriate function from the wrapped client and return its result.

Constraints

Do not modify the original clients.
The adapter must detect which client it’s wrapping.
The calling code should always use .upload() and .download().
No hardcoded conditionals like if (env === 'dev'); use method detection instead.

Sample output

The examples below illustrate what the output should look like:

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Node.js

// Simulated local file system client
const localFs = {
  save(file) {
    return `Saved ${file} locally`;
  },
  read(file) {
    return `Read ${file} from local disk`;
  }
};
// Simulated S3-like cloud client
const s3Client = {
  uploadFile(file) {
    return `Uploaded ${file} to S3`;
  },
  getFile(file) {
    return `Fetched ${file} from S3`;
  }
};
// Your code here
// Example usage
const localStorage = new StorageAdapter(localFs);
const cloudStorage = new StorageAdapter(s3Client);
console.log(localStorage.upload('report.pdf'));
console.log(localStorage.download('report.pdf'));
console.log(cloudStorage.upload('report.pdf'));
console.log(cloudStorage.download('report.pdf'));
/* Expected output:
Saved report.pdf locally
Read report.pdf from local disk
Uploaded report.pdf to S3
Fetched report.pdf from S3
*/