User Document Background Processing

Build a small user management system that uses background jobs to process uploaded documents, send notifications, run nightly cleanup, and handle retries — without blocking the public API.

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Table of Contents

• User Document Background Processing

  • Table of Contents
  • Requirements
  • Problem Description
  • Rules and Constraints
  • Core Scenarios
  • Input/Output and Examples
  • How to Run and Test
  • How to Submit (PR)
  • Evaluation Criteria
  • Timeline
  • Contact

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Requirements

• Allowed Language: C#

• Recommended Versions: .NET 6+

• OS: Any (Windows / Linux / macOS)

• You may use any background job / task scheduling library, such as:

  • Hangfire (recommended)
  • Quartz.NET
  • BackgroundService + custom scheduling logic

• Basic familiarity with:

  • RESTful APIs
  • Background job processing
  • Retry policies
  • File operations

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Problem Description

You are implementing a User Management System where users register via an API and upload a document file (any type such as image, Word, etc.). The system must behave as follows:

1. Accept user registration with an uploaded document.

2. Immediately return a fast response without waiting for heavy tasks.

3. Handle background jobs:

   • Send a welcome message immediately after registration.
   • Process the uploaded document after a 30-second delay, converting it to PDF (simulation allowed).
   • After successful processing, send a follow-up completion message.
   • Run a nightly cleanup at 00:00 to remove unused or incomplete files.

4. Apply an automatic retry policy for every job:

   • Maximum 2 retries
   • Retry #1 after 5 minutes
   • Retry #2 after 10 minutes (after the previous attempt)

5. Background tasks must never block the API.

Your job is to design and implement this workflow cleanly and maintainably.

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Rules and Constraints

• The POST /api/users/register API:

  • Must store user data + file metadata
  • Must enqueue background jobs
  • Must return immediately (201 Created)

• The 30-second delay must be implemented with delayed job scheduling.

• The nightly cleanup must be implemented as a recurring job (cron: 0 0 * * *).

• PDF conversion may be simulated (writing/copying dummy PDF file).

• Retry policy must be handled by the job library.

• Code must be clean, modular, and readable.

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Core Scenarios

1. User Registration API

• Endpoint: POST /api/users/register

• Input:

  • name, email
  • document file

• Behavior:

  1. Save user + file metadata
  2. Enqueue immediate job → Send Welcome Message
  3. Enqueue delayed job (30s) → Process Document
  4. Return success response quickly

2. Welcome Message Job

• Runs immediately
• Logs/Notifies: "Welcome !"
• Must not block API

3. Document Processing Job (Delayed 30s)

• Loads file metadata
• Converts to PDF (simulation allowed)
• Updates document status
• Enqueues completion message job

4. Completion Message Job

• Triggered after PDF creation
• Message: "Your document has been processed and is now available."

5. Nightly Cleanup Job (00:00)

• Runs daily at midnight
• Removes unused, orphan, stale files

6. Retry Policy

• Applies to all jobs
• Failure → retry 5 min → retry 10 min
• After exhaustion → log and persist

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Input/Output and Examples

Registration Request

POST /api/users/register HTTP/1.1
Content-Type: multipart/form-data
...

Response:

{
  "userId": "a1f9c570-0f3b-4d7d-9c35-0a0c12345678",
  "status": "Registered",
  "message": "User registered successfully."
}

Expected Timeline

T0      : Registration → HTTP 201
T0 + 0s : Welcome message
T0 +30s : Document processing
T0 +40s : PDF ready → completion message
00:00   : Nightly cleanup

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How to Run and Test

1) Clone

git clone https://github.com/<org>/<repo>.git
cd <repo>

2) Configure

• Configure Hangfire storage (SQL Server / Redis)
• Setup file storage paths

3) Build & Run

dotnet build
dotnet run

4) Tests

dotnet test

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How to Submit (PR)

1. Fork repository
2. Create branch:

git checkout -b solution/<username>

3. Place solution under:

solutions/C#/<username>/
  ├── source
  └── README.md

4. Create PR titled:

[Solution] User Document Background Processing - <username>

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Evaluation Criteria

Criteria	Weight
Correctness	40%
Code Quality	25%
Retry Logic	10%
API & Observability	10%
Documentation	5%
Early Submission	5%

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Timeline

• Start: 2025-11-30
• PR Submission Deadline: 2025-12-07

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Contact

• .NET / Backend Community Group
• Open an Issue in the repository for questions.