Internal Billing Library Reference

Purpose

Comprehensive reference for the internal billing library, documenting API usage, data models, integration patterns, and common operations for cost allocation and revenue recognition.

When to Use

• Cost Allocation: When allocating costs to different departments, projects, or customers
• Invoice Processing: When generating or processing invoices and billing statements
• Revenue Recognition: When implementing revenue recognition logic and reporting
• Usage Tracking: When tracking service usage for billing purposes
• Price Calculation: When calculating prices based on usage tiers, discounts, or custom pricing
• Integration Development: When integrating new services with the billing system
• Reporting: When generating billing reports and financial analytics

Library Overview

Core Components

BillingClient

Main client for interacting with the billing system:

python
from billing_lib import BillingClient

client = BillingClient(
    api_url="https://billing.internal.company.com",
    api_key="your-api-key",
    timeout=30
)

UsageTracker

Tracks and aggregates service usage:

python
from billing_lib import UsageTracker

tracker = UsageTracker(client)
usage = tracker.get_usage(
    service_id="web-api",
    customer_id="cust-123",
    period="2024-01"
)

PriceCalculator

Calculates costs based on usage and pricing rules:

python
from billing_lib import PriceCalculator

calculator = PriceCalculator()
cost = calculator.calculate_cost(
    usage_record=usage,
    pricing_tier="enterprise"
)

API Reference

Customer Management

Create Customer

python
customer = client.create_customer(
    name="Acme Corp",
    billing_email="billing@acme.com",
    address={
        "street": "123 Business St",
        "city": "San Francisco",
        "state": "CA",
        "zip": "94105",
        "country": "US"
    },
    metadata={"industry": "technology", "size": "enterprise"}
)

Get Customer

python
customer = client.get_customer(customer_id="cust-123")

Update Customer

python
customer = client.update_customer(
    customer_id="cust-123",
    billing_email="new-billing@acme.com"
)

Usage Tracking

Record Usage

python
usage_record = tracker.record_usage(
    service_id="web-api",
    customer_id="cust-123",
    usage_type="api_calls",
    quantity=1000,
    unit="calls",
    timestamp="2024-01-15T10:00:00Z",
    metadata={"endpoint": "/api/v1/users"}
)

Get Usage Summary

python
summary = tracker.get_usage_summary(
    customer_id="cust-123",
    start_date="2024-01-01",
    end_date="2024-01-31",
    group_by=["service_id", "usage_type"]
)

Invoice Generation

Generate Invoice

python
invoice = client.generate_invoice(
    customer_id="cust-123",
    period="2024-01",
    due_date="2024-02-15",
    line_items=[
        {
            "description": "API Usage",
            "quantity": 100000,
            "unit_price": 0.001,
            "total": 100.00
        }
    ]
)

Get Invoice

python
invoice = client.get_invoice(invoice_id="inv-456")

Data Models

Customer

python
@dataclass
class Customer:
    id: str
    name: str
    billing_email: str
    address: Address
    created_at: datetime
    updated_at: datetime
    metadata: Dict[str, Any]
    status: CustomerStatus  # ACTIVE, SUSPENDED, CANCELLED

UsageRecord

python
@dataclass
class UsageRecord:
    id: str
    service_id: str
    customer_id: str
    usage_type: str
    quantity: Decimal
    unit: str
    timestamp: datetime
    metadata: Dict[str, Any]

Invoice

python
@dataclass
class Invoice:
    id: str
    customer_id: str
    period: str
    status: InvoiceStatus  # DRAFT, SENT, PAID, OVERDUE
    total_amount: Decimal
    due_date: date
    line_items: List[LineItem]
    created_at: datetime

Gotchas

Common Pitfalls

• Decimal Precision: Always use Decimal for monetary calculations, never float
• Time Zone Handling: Usage timestamps must be in UTC for consistent reporting
• Idempotency: Usage recording should be idempotent to handle retries
• Rate Limiting: Billing API has rate limits, implement exponential backoff

Edge Cases

• Free Tiers: Handle free tier usage correctly to avoid billing errors
• Prorated Billing: Mid-month customer changes require prorated calculations
• Currency Conversion: Multi-currency billing requires real-time exchange rates
• Tax Calculation: Tax rules vary by jurisdiction and customer location

Performance Issues

• Large Usage Volumes: High-volume services may need batch processing
• Database Queries: Complex reporting queries can be slow, optimize indexes
• Memory Usage: Loading large customer datasets can consume significant memory
• API Timeouts: Long-running calculations may hit API timeouts

Security Considerations

• PII Protection: Customer billing information contains sensitive PII
• Access Control: Billing operations require proper authorization
• Audit Trail: All billing changes must be logged for compliance
• Data Encryption: Billing data should be encrypted at rest and in transit

Troubleshooting

• Duplicate Usage: Check for duplicate usage records causing over-billing
• Missing Invoices: Verify usage data is complete before invoice generation
• Calculation Errors: Validate pricing rules and tax calculations regularly
• Integration Failures: Monitor external system integrations for billing data

Integration Patterns

Service Integration

python
# Example: Integrating a new service
from billing_lib import UsageTracker, BillingClient

class MyServiceBilling:
    def __init__(self):
        self.client = BillingClient.from_config()
        self.tracker = UsageTracker(self.client)
    
    def track_api_usage(self, customer_id, endpoint, count):
        return self.tracker.record_usage(
            service_id="my-service",
            customer_id=customer_id,
            usage_type="api_calls",
            quantity=count,
            unit="calls",
            metadata={"endpoint": endpoint}
        )

Batch Processing

python
# Example: Processing usage in batches
def process_daily_usage():
    tracker = UsageTracker(BillingClient.from_config())
    
    # Get usage from monitoring system
    usage_data = get_usage_from_monitoring("2024-01-15")
    
    # Batch record usage
    batch_results = []
    for record in usage_data:
        try:
            result = tracker.record_usage(**record)
            batch_results.append(result)
        except Exception as e:
            logger.error(f"Failed to record usage: {e}")
    
    return batch_results

Configuration

Environment Variables

bash
BILLING_API_URL=https://billing.internal.company.com
BILLING_API_KEY=your-api-key
BILLING_TIMEOUT=30
BILLING_RETRY_ATTEMPTS=3
BILLING_BATCH_SIZE=100

Configuration File

yaml
billing:
  api_url: "https://billing.internal.company.com"
  api_key: "${BILLING_API_KEY}"
  timeout: 30
  retry_attempts: 3
  batch_size: 100
  
pricing:
  default_currency: "USD"
  tax_inclusive: false
  
reporting:
  timezone: "UTC"
  fiscal_month_start_day: 1

Testing

Unit Tests

python
import pytest
from billing_lib import BillingClient, UsageTracker
from unittest.mock import Mock, patch

class TestBillingClient:
    @pytest.fixture
    def client(self):
        return BillingClient(
            api_url="https://test.billing.com",
            api_key="test-key"
        )
    
    def test_create_customer(self, client):
        with patch.object(client, 'post') as mock_post:
            mock_post.return_value.json.return_value = {
                "id": "cust-123",
                "name": "Test Customer"
            }
            
            customer = client.create_customer(name="Test Customer")
            
            assert customer.id == "cust-123"
            assert customer.name == "Test Customer"

Integration Tests

python
class TestBillingIntegration:
    def test_end_to_end_billing(self):
        # Setup test customer
        customer = client.create_customer(
            name="Test Customer",
            billing_email="test@example.com"
        )
        
        # Record usage
        usage = tracker.record_usage(
            service_id="test-service",
            customer_id=customer.id,
            usage_type="api_calls",
            quantity=100
        )
        
        # Generate invoice
        invoice = client.generate_invoice(
            customer_id=customer.id,
            period="2024-01"
        )
        
        assert invoice.total_amount > 0
        assert len(invoice.line_items) > 0

References

Load these files when needed:

• scripts/billing-integration.py - Integration helpers and utilities
• scripts/usage-aggregator.py - Usage data aggregation and processing
• references/billing-api-spec.md - Complete API specification
• assets/pricing-rules.yaml - Pricing rule definitions and examples
• examples/integration-patterns/ - Service integration examples and patterns