Spec-driven Booking API with tests

[digitalPavel]

Summary

This PR implements a small appointment booking API using a spec-driven development approach with code generation tools.

The application supports creating and viewing appointments while enforcing domain rules such as time validation and overlap prevention.

Spec-Driven Approach

• Domain rules and API contract defined in Booking/booking.spec.md
• Implementation generated and refined from the spec
• Unit tests derived directly from the spec rules

Code Generation Tools

• GPT-5.2 / ChatGPT for domain model, service logic, and tests
• GitHub Copilot for scaffolding and refactoring

Prompts and workflow are documented in:
Booking/docs/codegen-log.md

Workflow Implemented

• POST /appointments — create appointment
• GET /appointments — list appointments

Domain rules enforced:

• EndUtc must be after StartUtc
• Minimum duration 15 minutes
• Cannot book in the past
• No overlapping appointments

Testing

Unit tests implemented using xUnit + FluentAssertions.

Run tests locally:

dotnet test

Run Application

dotnet run --project Booking/Booking.Api

Swagger UI is available at runtime at /swagger.

Notes

• In-memory storage (no database)
• No secrets or credentials
• Clean separation: Core / Infrastructure / Api