# ADR-0003: Architecture Decisions

> "Architecture is the art of how to waste space."
> — **Philip Johnson**

## Status
Accepted

## Context
The seedling template needs to make specific architectural decisions about project structure, file organization, and development patterns. These decisions will affect all projects generated from the template.

## Decision
Adopt specific architectural patterns and conventions for consistency and maintainability.

## Consequences

### **Project Structure**

#### **src/ Layout**
- **Why src/ layout?**
  - **Import clarity**: Prevents import confusion between package and test files
  - **Standard practice**: Industry standard for Python projects
  - **IDE support**: Better IDE support and autocomplete
  - **Testing clarity**: Clear separation between source and test code
  - **Packaging**: Easier to package and distribute

#### **Package Organization**
```
src/{{ project_slug }}/
├── __init__.py          # Package initialization
├── core/               # Core functionality
├── utils/              # Utility functions
├── config/             # Configuration management
└── models/             # Data models
```

### **Testing Strategy**

#### **Multi-level Testing**
- **Unit tests**: Fast, isolated tests for individual functions
- **Integration tests**: Tests for component interactions
- **End-to-end tests**: Full workflow testing
- **Property-based testing**: Hypothesis for edge case discovery

#### **Test Organization**
```
tests/
├── unit/               # Unit tests
├── integration/        # Integration tests
└── e2e/               # End-to-end tests
```

### **Documentation Architecture**

#### **Sphinx Configuration**
- **Furo theme**: Modern, responsive theme with dark mode
- **MyST parser**: Markdown support with extensions
- **API documentation**: Automatic API documentation generation
- **Search functionality**: Built-in search capabilities

#### **Documentation Structure**
```
docs/
├── source/             # Sphinx source files
│   ├── api.md         # API documentation
│   ├── contributing.md # Contributing guide
│   └── index.md       # Main documentation
├── build/             # Generated documentation
└── Makefile           # Documentation build commands
```

### **CI/CD Pipeline**

#### **GitHub Actions Workflows**
- **CI workflow**: Multi-environment testing with matrix strategy
- **Documentation workflow**: Automatic documentation deployment
- **Release workflow**: Automated PyPI publishing
- **Security workflow**: CodeQL security scanning
- **Static analysis**: Pre-commit-ci integration

#### **Quality Gates**
- **Linting**: Ruff for code quality
- **Type checking**: MyPy for type safety
- **Test coverage**: Minimum 80% coverage requirement
- **Security scanning**: pip-audit for vulnerability detection
- **Complexity analysis**: Xenon for code complexity

### **Configuration Management**

#### **Environment-based Configuration**
- **Development**: Local development settings
- **Testing**: Test-specific configuration
- **Production**: Production deployment settings
- **CI/CD**: Automated testing configuration

#### **Configuration Files**
- **pyproject.toml**: Project metadata and tool configuration
- **.pre-commit-config.yaml**: Pre-commit hooks configuration
- **noxfile.py**: Nox session definitions
- **justfile**: Development task definitions

### **Dependency Management**

#### **uv-based Dependencies**
- **Core dependencies**: Essential runtime dependencies
- **Development dependencies**: Development and testing tools
- **Documentation dependencies**: Documentation generation tools
- **Type checking dependencies**: Type checking tools
- **Security dependencies**: Security scanning tools

#### **Dependency Groups**
```toml
[project.optional-dependencies]
dev = ["pytest", "ruff", "mypy", "pre-commit"]
docs = ["sphinx", "furo", "myst-parser"]
typecheck = ["mypy", "types-requests"]
security = ["pip-audit"]
```

### **Code Quality Standards**

#### **Type Safety**
- **Full type hints**: All public APIs must have type hints
- **MyPy strict mode**: Zero type errors required
- **Type checking in CI**: Automated type checking in CI pipeline
- **Type coverage**: High type coverage requirements

#### **Code Style**
- **Black formatting**: Consistent code formatting
- **Ruff linting**: Comprehensive linting rules
- **Import sorting**: isort for import organization
- **Docstring standards**: Google or NumPy style docstrings

### **Security Considerations**

#### **Dependency Security**
- **Regular scanning**: Automated vulnerability scanning
- **Security updates**: Prompt security update process
- **Dependency pinning**: Pinned dependency versions
- **Audit trail**: Security audit documentation

#### **Code Security**
- **Static analysis**: CodeQL security scanning
- **Secret detection**: Pre-commit hooks for secret detection
- **Input validation**: Comprehensive input validation
- **Error handling**: Secure error handling practices

### **Performance Optimization**

#### **Build Performance**
- **Caching**: Effective caching strategies
- **Parallel execution**: Parallel test execution
- **Incremental builds**: Incremental documentation builds
- **Dependency optimization**: Optimized dependency resolution

#### **Runtime Performance**
- **Memory management**: Efficient memory usage
- **Algorithm optimization**: Optimized algorithms
- **Caching strategies**: Runtime caching where appropriate
- **Profiling**: Performance profiling tools

### **Extensibility Patterns**

#### **Plugin Architecture**
- **Registry pattern**: Extensible registry system
- **Hook system**: Plugin hook system
- **Configuration-driven**: Configuration-driven extensions
- **API stability**: Stable extension APIs

#### **Customization Points**
- **Template variables**: Jinja2 template variables
- **Conditional generation**: Conditional file generation
- **Custom workflows**: Customizable CI/CD workflows
- **Theme customization**: Customizable documentation themes

## Implementation Guidelines

### **File Naming Conventions**
- **Python files**: snake_case for modules and packages
- **Test files**: test_*.py for test modules
- **Configuration files**: kebab-case for configuration files
- **Documentation files**: kebab-case for documentation files

### **Code Organization**
- **Single responsibility**: Each module has a single responsibility
- **Dependency injection**: Use dependency injection for flexibility
- **Interface segregation**: Small, focused interfaces
- **Open/closed principle**: Open for extension, closed for modification

### **Error Handling**
- **Exception hierarchy**: Well-defined exception hierarchy
- **Error messages**: Clear, actionable error messages
- **Logging**: Comprehensive logging strategy
- **Recovery mechanisms**: Graceful error recovery

## Related ADRs
- [ADR-0001: Template Design Philosophy](./0001-template-design.md)
- [ADR-0002: Technology Stack Rationale](./0002-technology-stack.md)

## References
- [Python Packaging User Guide](https://packaging.python.org/)
- [Sphinx Documentation](https://www.sphinx-doc.org/)
- [GitHub Actions Documentation](https://docs.github.com/en/actions)
- [uv Documentation](https://docs.astral.sh/uv/)
- [Nox Documentation](https://nox.thea.codes/)
- [Just Documentation](https://just.systems/)