Pastebin-Lite

A robust, serverless pastebin application built with Next.js 15 and MongoDB. This application allows users to create text pastes that automatically expire based on time (TTL) or view counts.

🔗 Live Demo: https://aganitha-pastebin-lite-seven.vercel.app/

🌟 Features

• Create Pastes: Store arbitrary text content securely.
• Time-to-Live (TTL): Optional expiration time (in seconds). Pastes are automatically invalidated after the specified duration.
• View Limits: Optional maximum view count. The paste becomes completely unavailable (404) once the limit is reached.
• Atomic View Counting: Uses MongoDB atomic operators to strictly enforce view limits, preventing race conditions under concurrent load.
• Deterministic Testing: Supports the x-test-now-ms header (in Test Mode) to simulate time travel for automated grading.

🛠 Tech Stack

• Framework: Next.js 15 (App Router)
• Language: TypeScript
• Database: MongoDB (via Mongoose ODM)
• Styling: Tailwind CSS
• Deployment: Vercel (Recommended)

🚀 Getting Started

Follow these instructions to run the project locally.

Prerequisites

• Node.js 18+ installed.
• A MongoDB connection string (Local or Atlas).

Installation

1. Clone the repository:

   git clone [https://github.com/YOUR_GITHUB_USERNAME/pastebin-lite.git](https://github.com/YOUR_GITHUB_USERNAME/pastebin-lite.git)
   cd pastebin-lite

2. Install dependencies:

   npm install

3. Configure Environment Variables: Create a .env.local file in the root directory and add your MongoDB credentials:

   # MongoDB Connection String
   MONGODB_URI="mongodb+srv://<username>:<password>@cluster0.mongodb.net/pastebin-lite"
   
   # Set to "1" to enable deterministic time testing via headers
   TEST_MODE="1"

4. Run the Development Server:

   npm run dev

5. Access the App: Open http://localhost:3000 in your browser.

💾 Persistence Layer

Choice: MongoDB (Mongoose)

I selected MongoDB for this project for two primary reasons:

1. Document Model: The data structure for a paste (content, metadata, flexible expiration settings) maps perfectly to a JSON-like document model.
2. Atomic Operations: To satisfy the strict "Max Views" requirement, I utilized MongoDB's findOneAndUpdate with the $inc operator. This ensures that checking the view count and incrementing it happens in a single atomic transaction. This guarantees that even if two users request the paste at the exact same millisecond, the database will never serve the paste more times than allowed.

🏗 Notable Design Decisions

• Next.js 15 & Promise Handling: This project uses the latest Next.js 15. As per the new architecture, dynamic route parameters (params) are treated as Promises. The code explicitly awaits these params in both API routes and UI components to ensure stable rendering.
• Server-Side Logic: All sensitive logic (checking expiry, incrementing views) is handled securely on the server (API Routes) before returning data to the client.
• Time Travel Logic: A custom helper (lib/time.ts) injects the x-test-now-ms time into the expiry check only when TEST_MODE=1 is set. This separates test logic from production logic while meeting the assignment's grading requirements.

📡 API Endpoints

1. Health Check

• GET /api/healthz
• Returns: 200 OK { "ok": true } if the database is connected.

2. Create Paste

• POST /api/pastes
• Body:

  {
    "content": "Hello World",
    "ttl_seconds": 60,   // Optional
    "max_views": 5       // Optional
  }

• Returns: { "id": "...", "url": "..." }

3. Get Paste

• GET /api/pastes/:id
• Returns: Paste content and metadata.
• Errors: Returns 404 if the paste is expired or the view limit is exceeded.

📂 Project Structure

├── app/
│   ├── api/            # Backend API Routes
│   ├── p/[id]/         # View Paste Page (Dynamic Route)
│   └── page.tsx        # Create Paste Page (Home)
├── lib/
│   ├── db.ts           # MongoDB Connection Helper
│   └── time.ts         # Deterministic Time Helper
├── models/
│   └── Paste.ts        # Mongoose Data Schema
└── public/