Expenses Tracker API

The Expense Tracker API is a RESTful API designed to help users manage their personal or organizational expenses. It includes features for:

• Tracking expenses
• Setting and monitoring a budget
• Configuring recurring expenses
• Triggering webhook notifications when the budget is exceeded

This project also integrates with a Webhook Test Server, which receives alerts when expenses go over the defined budget.

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🚀 Features

• 📦 Add, retrieve, and manage expenses
• 🎯 Set a budget
• 🔁 Add recurring expenses
• 📬 Trigger real-time webhook notifications when budget is exceeded

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📘 API Endpoints

🔧 POST /setup

• Purpose: Set the webhook URL to receive notifications.
• Request Body:

{
  "webhookUrl": "http://localhost:5555"
}

• Responses:
  • 200 OK – Webhook URL accepted
  • 400 Bad Request – Invalid URL format

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💰 POST /expenses

• Purpose: Add a new expense.
• Request Body:

{
  "amount": 50,
  "category": "food"
}

• Responses:
  • 201 Created

If the total of all expenses exceeds the current budget, a notification is sent to the webhook.

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📋 GET /expenses

• Purpose: Retrieve all recorded expenses.
• Response:

{
  "expenses": [
    {
      "amount": 50,
      "category": "food",
      "timestamp": 1711492393000
    }
  ]
}

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🎯 POST /budget

• Purpose: Set or update the budget limit.
• Request Body:

{
  "amount": 100
}

• Response:

{
  "message": "Budget set successfully"
}

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🔁 POST /recurring

• Purpose: Add a recurring expense.
• Request Body:

{
  "amount": 20,
  "category": "subscription",
  "intervalInSeconds": 5
}

• Response:

{
  "message": "Recurring expense added"
}

Each recurring expense is added to /expenses on a repeating interval. If cumulative expenses exceed the budget, a notification is sent.

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🔁 GET /recurring

• Purpose: Retrieve all recurring expenses.
• Response:

{
  "recurringExpenses": [
    {
      "amount": 20,
      "category": "subscription",
      "intervalInSeconds": 5,
      "lastRun": 1711492393000
    }
  ]
}

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📬 Webhook Integration

When expenses exceed the set budget (either by direct or recurring additions), a POST request is sent to:

POST <webhookUrl>/notifications

Payload:

{
  "message": "Budget exceeded",
  "total": 210,
  "expenses": [
    { "amount": 50, "category": "food", "timestamp": 1711492393000 },
    { "amount": 160, "category": "electronics", "timestamp": 1711492493000 }
  ]
}

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✅ Completion Criteria

Your implementation will be evaluated against the following:

• Correctly setting up the webhook via /setup
• Validating and rejecting malformed webhook URLs
• Adding and retrieving expenses
• Setting and enforcing budget limits
• Sending budget-exceeded notifications to the webhook
• Managing recurring expenses and ensuring they run at proper intervals
• Triggering notifications from recurring expense overflow