Invoice Generation

Skill Profile

(Select at least one profile to enable specific modules)

• DevOps
• Backend
• Frontend
• AI-RAG
• Security Critical

Overview

This skill provides comprehensive patterns for generating invoices in billing systems. It covers invoice data structure, PDF generation using PDFKit and Puppeteer, invoice templates, line item calculation, tax calculation, invoice numbering, storage and retrieval, email delivery, status tracking, and compliance requirements.

Why This Matters

• Professionalism: Professional invoices build customer trust
• Compliance: Proper invoices meet tax and accounting requirements
• Automation: Automated generation reduces manual overhead
• Customer Experience: Timely invoice delivery improves cash flow

Core Concepts & Rules

1. Core Principles

• Follow established patterns and conventions
• Maintain consistency across codebase
• Document decisions and trade-offs

2. Implementation Guidelines

• Start with the simplest viable solution
• Iterate based on feedback and requirements
• Test thoroughly before deployment

Inputs / Outputs / Contracts

• Inputs:
  • Environment variables:

    PDF_STORAGE_PATH

    ,

    EMAIL_FROM

    ,

    SMTP_HOST

  • Configuration: invoice template, tax rates, invoice number format
  • Database schema: invoices, invoice_line_items, invoice_taxes
• Entry Conditions:
  • Database tables created for invoices
  • PDF generation library installed
  • Email service configured
• Outputs:
  • Generated PDF invoices
  • Invoice records in database
  • Email delivery confirmations
• Artifacts Required (Deliverables):
  • Invoice data models
  • PDF generation service
  • Invoice template system
  • Email delivery service
• Acceptance Evidence:
  • Test coverage report (>80%)
  • PDF generation verification
  • Email delivery tests
• Success Criteria:
  • Invoices generate correctly with all line items
  • PDFs are properly formatted
  • Emails are delivered successfully
  • Invoice status updates correctly

Skill Composition

• Depends on: billing-cycles, subscription-plans
• Compatible with: usage-metering, stripe-integration
• Conflicts with: None
• Related Skills: webhook-handling, email-templates

Quick Start / Implementation Example

1. Review requirements and constraints
2. Set up development environment
3. Implement core functionality following patterns
4. Write tests for critical paths
5. Run tests and fix issues
6. Document any deviations or decisions

# Example implementation following best practices
def example_function():
    # Your implementation here
    pass

Assumptions / Constraints / Non-goals

• Assumptions:
  • Development environment is properly configured
  • Required dependencies are available
  • Team has basic understanding of domain
• Constraints:
  • Must follow existing codebase conventions
  • Time and resource limitations
  • Compatibility requirements
• Non-goals:
  • This skill does not cover edge cases outside scope
  • Not a replacement for formal training

Compatibility & Prerequisites

• Supported Versions:
  • Python 3.8+
  • Node.js 16+
  • Modern browsers (Chrome, Firefox, Safari, Edge)
• Required AI Tools:
  • Code editor (VS Code recommended)
  • Testing framework appropriate for language
  • Version control (Git)
• Dependencies:
  • Language-specific package manager
  • Build tools
  • Testing libraries
• Environment Setup:

  • .env.example

    keys:

    API_KEY

    ,

    DATABASE_URL

    (no values)

Test Scenario Matrix (QA Strategy)

Technical Guardrails & Security Threat Model

1. Security & Privacy (Threat Model)

• Top Threats: Injection attacks, authentication bypass, data exposure

• Data Handling: Sanitize all user inputs to prevent Injection attacks. Never log raw PII
• Secrets Management: No hardcoded API keys. Use Env Vars/Secrets Manager
• Authorization: Validate user permissions before state changes

2. Performance & Resources

• Execution Efficiency: Consider time complexity for algorithms
• Memory Management: Use streams/pagination for large data
• Resource Cleanup: Close DB connections/file handlers in finally blocks

3. Architecture & Scalability

• Design Pattern: Follow SOLID principles, use Dependency Injection
• Modularity: Decouple logic from UI/Frameworks

4. Observability & Reliability

• Logging Standards: Structured JSON, include trace IDs

  request_id

• Metrics: Track

  error_rate

  ,

  latency

  ,

  queue_depth

• Error Handling: Standardized error codes, no bare except
• Observability Artifacts:
  • Log Fields: timestamp, level, message, request_id
  • Metrics: request_count, error_count, response_time
  • Dashboards/Alerts: High Error Rate > 5%

Agent Directives & Error Recovery

(ข้อกำหนดสำหรับ AI Agent ในการคิดและแก้ปัญหาเมื่อเกิดข้อผิดพลาด)

• Thinking Process: Analyze root cause before fixing. Do not brute-force.
• Fallback Strategy: Stop after 3 failed test attempts. Output root cause and ask for human intervention/clarification.
• Self-Review: Check against Guardrails & Anti-patterns before finalizing.
• Output Constraints: Output ONLY the modified code block. Do not explain unless asked.

Definition of Done (DoD) Checklist

• Tests passed + coverage met
• Lint/Typecheck passed
• Logging/Metrics/Trace implemented
• Security checks passed
• Documentation/Changelog updated
• Accessibility/Performance requirements met (if frontend)

Anti-patterns / Pitfalls

• ⛔ Don't: Log PII, catch-all exception, N+1 queries
• ⚠️ Watch out for: Common symptoms and quick fixes
• 💡 Instead: Use proper error handling, pagination, and logging

Reference Links & Examples

• Internal documentation and examples
• Official documentation and best practices
• Community resources and discussions

Versioning & Changelog

• Version: 1.0.0
• Changelog:
  • 2026-02-22: Initial version with complete template structure