feat: implement add note to budget command and handler

[Dennoh12]

Backend Development Understanding

I implemented a CQRS command pattern for adding notes to budgets. The pattern separates write operations (commands) from read operations (queries).

Design Choices

Command Class:

• Made all properties readonly for immutability
• Included budgetId, noteContent, and authorId as required fields
• Made createdAt optional (handler can set it if not provided)

Handler Class:

• Implemented ICommandHandler interface for consistency
• Separated validation into its own method for clarity
• Used private methods to organize code logically
• Added comprehensive error handling with try-catch

Validation:

• Check for empty/null values
• Validate content length (max 5000 characters)
• Provide clear error messages

Deployment on Current Architecture

Based on Kujali's Firebase/Google Cloud setup:

1. Package this library as a Cloud Function
2. Deploy using: firebase deploy --only functions:addNoteToBudget
3. Frontend would call it via firebase.functions().httpsCallable()

Serverless Deployment Knowledge

Serverless means no server management - the cloud provider runs code on-demand.

How it scales:

• Each request spawns a new function instance automatically
• Can handle 1 or 1000 requests simultaneously
• Pay only for execution time (very cost-effective)
• Automatic load balancing

Trade-offs:

• ✅ No infrastructure to manage
• ✅ Automatic scaling
• ✅ Pay per use
• ❌ Cold start latency (first request slower)
• ❌ Execution time limits (max 9 minutes)