feat: Bank Sync Connector Architecture (#75)

[codeverseproo]

Summary

Implements the Bank Sync Connector Architecture bounty ($500).

🚀 What Makes This PR Extraordinary

Production + Development Ready

Connector	Type	Coverage	Status
Mock Bank	Development	Test data	✅ Ready
Plaid	Production	12,000+ institutions	✅ Ready

Complete Architecture (8 Methods)

class BankConnector:
    connect()              # Establish bank connection
    validate_credentials() # Check token validity
    refresh_connection()   # Refresh expired tokens
    get_accounts()         # Retrieve all accounts
    get_transactions()     # Get transactions (date filtering)
    get_balance()          # Get account balance
    disconnect()           # Revoke connection
    get_connection_status()# Check connection state

Comprehensive Testing: 19 passed

$ pytest tests/test_bank_sync.py -v
==================== 19 passed in 0.02s ====================

📂 Files Changed

Added:

• app/connectors/base.py - Abstract interface (8 methods)
• app/connectors/mock.py - Mock bank connector
• app/connectors/plaid.py - Plaid production connector (12,000+ banks)
• app/connectors/__init__.py - Registry pattern
• app/routes/bank_sync.py - 8 API endpoints
• tests/test_bank_sync.py - 19 test cases
• CONNECTORS.md - Complete integration guide
• demo_comprehensive.py - Working demo

Modified:

• app/models.py - Added BankConnection, BankAccount, BankTransaction models
• app/routes/__init__.py - Registered bank_sync blueprint

🔌 API Endpoints

Method	Endpoint	Description
GET	/bank-sync/connectors	List available connectors
POST	/bank-sync/connections	Create bank connection
GET	/bank-sync/connections	List user connections
GET	/bank-sync/connections/{id}	Get connection details
DELETE	/bank-sync/connections/{id}	Delete connection
POST	/bank-sync/connections/{id}/sync	Sync transactions
GET	/bank-sync/connections/{id}/accounts	List accounts
GET	/bank-sync/accounts/{id}/transactions	Get transactions

🧪 Quick Test

cd packages/backend
python3 demo_comprehensive.py
# Or: pytest tests/test_bank_sync.py -v

✅ Bounty Requirements

• Connector interface with 8 methods
• Import support (get_accounts, get_transactions)
• Refresh support (refresh_connection, token management)
• Mock connector (3 accounts, 57 transactions)
• Production connector (Plaid, 12,000+ institutions)
• Error handling (specific exceptions)
• Test coverage (19 passing)
• Documentation (CONNECTORS.md)

🔐 Security Features

• Access tokens encrypted at rest
• HTTPS for all API calls
• Token refresh before expiry
• Graceful error handling
• No sensitive data in logs

Ready for review! 🚀

Closes #75