Implementation Plan: Budget Application

Overview

This implementation plan follows an end-to-end delivery approach, building a working web application that can be loaded in the browser from day one. Each feature is implemented completely (frontend + backend + database) before moving to the next feature. This ensures continuous user testing and validation rather than theoretical functionality.

Development Philosophy

End-to-End Feature Delivery:

• Start with a deployable “Hello World” application
• Add one complete feature at a time (UI + API + database)
• Every increment should be testable in the browser
• Prioritize working software over comprehensive testing initially
• User testing (by you) drives iteration, not unit tests

Feature Priority Order:

1. Core transaction tracking (accounts → transactions → balances)
2. Transaction management (editing, deletion)
3. Categorization for analysis
4. Planning and forecasting
5. Advanced budgeting (pots, goals)

Tasks

Phase 1: Deployable Foundation

• [ ] 1. Create minimal deployable application

  • Set up CDK infrastructure (Lambda, API Gateway, DynamoDB, S3, CloudFront)
  • Create “Hello World” HTML page served from Lambda
  • Deploy to AWS and verify it loads in browser
  • Set up basic TypeScript build and deployment pipeline
  • Requirements: 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7

• [ ] 2. Set up basic application structure

  • Create core library structure with minimal interfaces
  • Set up HTTP request routing and basic error handling
  • Add DynamoDB connection and basic table structure
  • Create simple HTML template system for pages
  • Requirements: 21.1, 21.2, 21.6, 21.7

Phase 2: Account Management

• [ ] 3. Implement account creation (end-to-end)

  • [ ] 3.1 Create account creation UI

    • Add HTML form for account name, description, notes
    • Style with basic CSS for usable interface
    • Requirements: 13.1, 13.2

  • [ ] 3.2 Implement account creation backend

    • Create AccountService.create() method with DynamoDB storage
    • Generate UUIDs and store account metadata with versioning
    • Include userId in database keys for security
    • Requirements: 4.1, 4.2, 4.3, 22.1, 22.2, 22.4

  • [ ] 3.3 Wire account creation form to backend

    • Handle form submission and validation
    • Display success/error messages to user
    • Redirect to account list after successful creation
    • Requirements: 12.1, 12.2, 12.8

• [ ] 4. Implement account listing (end-to-end)

  • [ ] 4.1 Create account listing UI

    • Display all accounts with names and metadata
    • Show account balances (initially zero)
    • Add navigation to account creation form
    • Requirements: 13.1, 13.3

  • [ ] 4.2 Implement account listing backend

    • Create AccountService.list() method
    • Calculate and display account balances
    • Requirements: 4.4, 4.5

  • [ ] 4.3 Test complete account workflow

    • Verify account creation and listing works end-to-end
    • Test in deployed environment, not just locally
    • Requirements: 18.2, 18.8

Phase 3: Transaction Creation

• [ ] 5. Implement transaction creation (end-to-end)

  • [ ] 5.1 Create transaction creation UI

    • Add form for amount, date, type (income/expense/transfer)
    • Include source/destination account selection
    • Add description and notes fields
    • Requirements: 14.7

  • [ ] 5.2 Implement transaction event creation backend

    • Create EventService for ULID-ordered event creation
    • Create TransactionService.create() that generates events
    • Store events in DynamoDB with proper key patterns
    • Requirements: 9.1, 9.2, 9.7, 10.1, 22.1, 22.2

  • [ ] 5.3 Wire transaction creation to backend

    • Handle form validation (positive amounts, valid dates, endpoint selection)
    • Create transaction creation events
    • Display success/error feedback
    • Requirements: 10.2, 10.9, 10.10, 12.1, 12.3

Phase 4: State Calculation and Balance Display

• [ ] 6. Implement transaction-to-state calculation

  • [ ] 6.1 Create state calculation engine

    • Implement event stream processing to reconstruct transactions
    • Apply transactions to calculate account balances
    • Handle transaction type ordering (income → transfers → expenses)
    • Requirements: 11.1, 11.2, 11.3, 11.4

  • [ ] 6.2 Update account listing with real balances

    • Connect account listing to state calculation
    • Display current balances based on transactions
    • Requirements: 4.4, 13.3

  • [ ] 6.3 Test transaction creation and balance updates

    • Create transactions and verify balances update correctly
    • Test different transaction types and amounts
    • Requirements: 10.8, 11.1

Phase 5: Transaction Listing and Monthly Views

• [ ] 7. Implement transaction listing (end-to-end)

  • [ ] 7.1 Create transaction listing UI

    • Display transactions for current month by default
    • Show transaction details (date, amount, type, description)
    • Display running balance calculations
    • Requirements: 14.1, 14.5, 14.6

  • [ ] 7.2 Implement transaction listing backend

    • Create TransactionService.list() with date filtering
    • Support account-specific transaction filtering
    • Calculate running balances for display
    • Requirements: 14.1, 14.5, 14.6

  • [ ] 7.3 Wire transaction listing to UI

    • Connect backend transaction queries to frontend display
    • Show starting balance, ending balance, and running totals
    • Requirements: 14.6

Phase 6: Navigation and Month Selection

• [ ] 8. Implement month and account navigation

  • [ ] 8.1 Add month navigation controls

    • Create previous/next month navigation
    • Display current year and month clearly
    • Preserve account selection when changing months
    • Requirements: 14.2, 14.3

  • [ ] 8.2 Add account selection dropdown

    • Create account selection dropdown in transaction view
    • Preserve month selection when changing accounts
    • Support “all accounts” view
    • Requirements: 14.4

  • [ ] 8.3 Test complete navigation workflow

    • Verify month navigation works correctly
    • Test account filtering and selection
    • Ensure URL parameters work for bookmarking
    • Requirements: 14.2, 14.3, 14.4

Checkpoint: Working Transaction Tracking System At this point, you have a fully functional transaction tracking application that provides real user value.

Phase 7: Account Metadata Management

• [ ] 9. Implement account editing

  • [ ] 9.1 Create account editing UI

    • Add edit forms for account name, description, notes
    • Support account activation/deactivation
    • Requirements: 13.2, 20.1, 20.5

  • [ ] 9.2 Implement account metadata updates

    • Create AccountService.update() with metadata versioning
    • Handle conditional updates to prevent conflicts
    • Requirements: 4.6, 3.8

  • [ ] 9.3 Wire account editing to backend

    • Handle form submission and validation
    • Display updated account information
    • Requirements: 13.2

Phase 8: Transaction Management

• [ ] 10. Implement transaction editing

  • [ ] 10.1 Create transaction editing UI

    • Add edit forms for existing transactions
    • Support changing amount, date, description, accounts
    • Requirements: 14.7

  • [ ] 10.2 Implement transaction update events

    • Create TransactionService.update() that generates update events
    • Preserve transaction history through event sourcing
    • Requirements: 9.3, 10.8

  • [ ] 10.3 Wire transaction editing to backend

    • Handle transaction updates and validation
    • Refresh transaction list and balances after updates
    • Requirements: 10.8

• [ ] 11. Implement transaction deletion

  • [ ] 11.1 Add transaction deletion UI

    • Add delete buttons/confirmation dialogs
    • Requirements: 14.7

  • [ ] 11.2 Implement transaction deletion events

    • Create TransactionService.delete() that generates delete events
    • Maintain audit trail through event sourcing
    • Requirements: 9.4

  • [ ] 11.3 Wire transaction deletion to backend

    • Handle deletion requests and confirmation
    • Update transaction list and balances after deletion
    • Requirements: 9.4

Phase 9: Category Support

• [ ] 12. Implement category management (end-to-end)

  • [ ] 12.1 Create category management UI

    • Add category creation and listing interface
    • Support category editing and activation/deactivation
    • Requirements: 15.1, 15.2, 15.3

  • [ ] 12.2 Implement category backend services

    • Create CategoryService with CRUD operations
    • Include metadata versioning and active status
    • Requirements: 7.1, 7.2, 7.5, 20.1

  • [ ] 12.3 Add category selection to transactions

    • Update transaction forms to include category selection
    • Display categories in transaction listings
    • Requirements: 14.7

Checkpoint: Complete Transaction Management System At this point, you have a fully functional transaction management system with categorization.

Phase 10: Plan Creation and Management

• [ ] 13. Implement plan creation (end-to-end)

  • [ ] 13.1 Create plan creation UI

    • Add forms for plan metadata (name, amount, source, destination)
    • Support schedule configuration (one-time, monthly, weekly)
    • Include weekend adjustment options
    • Requirements: 16.1, 16.2

  • [ ] 13.2 Implement plan backend services

    • Create PlanService with scheduling logic
    • Calculate next execution dates based on plan type
    • Requirements: 6.1, 6.2, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, 6.10

  • [ ] 13.3 Wire plan creation to backend

    • Handle plan creation and validation
    • Display created plans in management interface
    • Requirements: 16.3

Phase 11: Combined Transaction Views (Realized + Planned)

• [ ] 14. Implement planned transaction generation

  • [ ] 14.1 Create planned transaction calculation

    • Implement PlanService.generatePlannedTransactions()
    • Generate future transactions based on active plans
    • Respect lastRealizedDate to prevent duplicates
    • Requirements: 6.19, 6.20

  • [ ] 14.2 Update transaction listing to show planned transactions

    • Display both realized and planned transactions
    • Visually distinguish planned vs realized transactions
    • Requirements: 14.5

  • [ ] 14.3 Update balance calculations for planned transactions

    • Include planned transactions in balance projections
    • Show projected balances for future months
    • Requirements: 11.1

Phase 12: Plan Realization

• [ ] 15. Implement plan realization

  • [ ] 15.1 Create plan realization UI

    • Add buttons/interface to realize planned transactions
    • Support batch realization up to specific dates
    • Requirements: 16.2

  • [ ] 15.2 Implement plan realization backend

    • Create PlanService.realize() method
    • Convert planned transactions to actual transaction events
    • Update lastRealizedDate tracking
    • Requirements: 6.18, 6.19

  • [ ] 15.3 Wire plan realization to UI

    • Handle realization requests and confirmation
    • Update transaction views after realization
    • Requirements: 16.2

Phase 13: Plan Management

• [ ] 16. Implement plan updates and lifecycle management

  • [ ] 16.1 Create plan editing UI

    • Support editing plan metadata and schedules
    • Add plan activation/deactivation controls
    • Requirements: 16.2, 16.3

  • [ ] 16.2 Implement plan update backend

    • Create plan update methods with versioning
    • Handle plan deactivation and reactivation
    • Requirements: 6.11, 6.12, 6.13

  • [ ] 16.3 Wire plan management to backend

    • Handle plan updates and status changes
    • Refresh planned transaction views after changes
    • Requirements: 16.3

Checkpoint: Complete Planning and Forecasting System At this point, you have a fully functional system for planning and forecasting transactions.

Phase 14: Pot Support

• [ ] 17. Implement pot management (end-to-end)

  • [ ] 17.1 Create pot management UI

    • Add pot creation forms with parent account selection
    • Display pots within their parent accounts
    • Requirements: 13.1, 13.3

  • [ ] 17.2 Implement pot backend services

    • Create PotService with parent account relationships
    • Implement pot balance constraints (no negative balances)
    • Handle pot overflow to parent account
    • Requirements: 5.1, 5.2, 5.4, 5.5, 5.6, 5.7

  • [ ] 17.3 Update transaction system for pot support

    • Add pot selection to transaction forms
    • Update balance calculations for pot constraints
    • Requirements: 5.7, 10.3, 10.4, 10.5

Phase 15: Goal Support

• [ ] 18. Implement goal management (end-to-end)

  • [ ] 18.1 Create goal management UI

    • Add goal creation forms for pots
    • Display goal progress and required contributions
    • Support manual achievement marking
    • Requirements: 13.4

  • [ ] 18.2 Implement goal backend services

    • Create GoalService with achievement tracking
    • Calculate required periodic contributions
    • Handle manual achievement status changes
    • Requirements: 8.1, 8.2, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9, 8.10, 8.11, 8.12

  • [ ] 18.3 Wire goal management to UI

    • Display goal progress in pot listings
    • Show achievement status and contribution requirements
    • Requirements: 13.4

Phase 16: Production Readiness

• [ ] 19. Add authentication and production features

  • [ ] 19.1 Implement Cognito authentication

    • Add user registration and login flows
    • Implement JWT token handling and refresh
    • Requirements: 1.8, 1.9, 1.10, 1.11

  • [ ] 19.2 Add multi-user and multi-budget support

    • Implement user isolation and budget management
    • Add budget creation and selection UI
    • Requirements: 2.1, 2.2, 2.3, 2.4, 2.5, 2.6

  • [ ] 19.3 Production deployment and monitoring

    • Set up production environment with authentication
    • Add monitoring, logging, and error tracking
    • Requirements: 18.5, 18.6

Notes

• Every task delivers working functionality that can be tested in the browser
• Each phase builds incrementally on the previous phase
• User testing drives iteration rather than theoretical unit tests
• Authentication is added only at the end to simplify development
• The system provides real user value starting from Phase 6