# Design Document

## Overview

Phase 1 establishes the foundational infrastructure for mypylogger v0.2.0, implementing a modern Python development environment with UV-based dependency management, comprehensive testing infrastructure, and strict quality gates. The design prioritizes developer experience, reproducible builds, and automated quality enforcement.

## Architecture

### Project Structure Design

```
mypylogger/
├── .git/                   # Git version control
├── .gitignore             # Python-specific ignore patterns
├── .kiro/                 # AI assistant configuration and steering
│   ├── steering/          # Development guidance documents
│   └── specs/             # Feature specifications
├── pyproject.toml         # Project configuration and dependencies
├── uv.lock               # UV lock file for reproducible builds
├── README.md             # Project overview and quick start
├── src/                  # Source code (src layout)
│   └── mypylogger/       # Main package directory
│       └── __init__.py   # Package initialization
├── tests/                # Test files
│   ├── unit/             # Unit tests
│   ├── integration/      # Integration tests
│   └── conftest.py       # Shared test fixtures
├── scripts/              # Build and development scripts
│   └── run_tests.sh      # Master test runner script
└── main.py              # Development entry point
```

### Dependency Management Architecture

**UV-Centric Approach:**
- All Python operations use `uv run` prefix for environment isolation
- Single runtime dependency: `python-json-logger`
- Development dependencies managed in `[dependency-groups]` section
- Lock file (`uv.lock`) committed for reproducible builds across environments

**Dependency Categories:**
- **Runtime**: `python-json-logger` (JSON formatting capability)
- **Testing**: `pytest`, `pytest-cov` (test execution and coverage)
- **Code Quality**: `ruff` (linting and formatting), `mypy` (type checking)

## Components and Interfaces

### Development Tool Integration

**Ruff Integration:**
- Combined linter and formatter for comprehensive code quality
- Configured for 100-character line length with 120-character hard limit
- Automatic import sorting and style enforcement
- Integration with VSCode extension for real-time feedback

**pytest Integration:**
- Unit tests in `tests/unit/` for fast feedback (<1 second)
- Integration tests in `tests/integration/` for workflow validation
- Coverage reporting with 95% minimum threshold
- Shared fixtures in `conftest.py` for test consistency

**mypy Integration:**
- Static type checking for all source code
- Strict configuration to catch type-related issues early
- Integration with development workflow for continuous validation

### Quality Gate System

**Master Test Script (`./scripts/run_tests.sh`):**
- Comprehensive validation of all quality criteria
- Sequential execution: tests → coverage → linting → formatting → type checking
- Non-zero exit codes on any failure (fail-fast approach)
- Detailed reporting for debugging failed checks
- Success summary when all checks pass

**Individual Tool Commands:**
- `uv run pytest --cov=mypylogger --cov-fail-under=95` - Test execution with coverage
- `uv run ruff format .` - Code formatting
- `uv run ruff check .` - Linting validation
- `uv run mypy src/` - Type checking

## Data Models

### Project Configuration (pyproject.toml)

```toml
[project]
name = "mypylogger"
version = "0.2.0"
description = "Zero-dependency JSON logging with sensible defaults"
requires-python = ">=3.8"
dependencies = ["python-json-logger>=4.0.0"]

[dependency-groups]
dev = ["pytest>=8.3.5", "pytest-cov>=5.0.0", "ruff>=0.14.1", "mypy>=1.14.1"]

[build-system]
requires = ["hatchling"]
build-backend = "hatchling.build"
```

### Package Structure

**Source Layout:**
- `src/mypylogger/__init__.py` - Package entry point and public API
- Future modules will be added under `src/mypylogger/` as development progresses
- Import pattern: `from mypylogger import get_logger`

**Test Organization:**
- `tests/unit/` - Fast, isolated unit tests
- `tests/integration/` - End-to-end workflow tests
- `tests/conftest.py` - Shared fixtures and test configuration

## Error Handling

### Development Environment Errors

**UV Command Failures:**
- Clear error messages when UV commands fail
- Fallback suggestions for common issues (missing UV installation)
- Environment validation before executing development commands

**Dependency Resolution Issues:**
- Lock file conflicts resolved through `uv sync`
- Clear documentation of dependency requirements
- Minimal dependency policy to reduce resolution complexity

**Quality Gate Failures:**
- Master test script provides specific failure information
- Individual tool commands available for targeted debugging
- Non-zero exit codes prevent accidental task completion with failures

### Build and Distribution Errors

**Package Structure Issues:**
- Validation that src/ layout is properly configured
- Import path verification during development
- Build system compatibility checks

**Configuration Errors:**
- pyproject.toml validation during UV operations
- Clear error messages for configuration issues
- Documentation of required configuration sections

## Testing Strategy

### Test-Driven Development (TDD) Approach

**TDD Cycle Implementation:**
1. **Red Phase**: Write failing test that defines desired behavior
2. **Green Phase**: Implement minimal code to make test pass
3. **Refactor Phase**: Improve code while maintaining test success
4. **Validation**: Run master test script to ensure all quality gates pass

**Test Categories:**

**Unit Tests (Fast Feedback):**
- Individual function and class testing
- Mocked external dependencies
- Target: <1 second total execution time
- 100% coverage of core logic paths

**Integration Tests (Workflow Validation):**
- Component interaction testing
- Real filesystem and environment usage
- End-to-end user workflow validation
- Target: <30 seconds total execution time

### Coverage Requirements

**95% Minimum Coverage:**
- Enforced by master test script
- Measured using pytest-cov
- HTML reports available for detailed analysis
- Coverage gaps must be justified or addressed

**Coverage Exclusions:**
- Test files themselves
- Development scripts and utilities
- Error handling for truly exceptional cases (with justification)

### Quality Assurance Integration

**Continuous Validation:**
- All development commands use `uv run` prefix
- Quality gates run before any task completion
- Master test script as definitive validation
- Zero tolerance for quality gate failures

**Development Workflow Integration:**
- TDD cycle includes quality gate validation
- Automated formatting before manual corrections
- Type checking integrated into development loop
- Git commits only after all quality gates pass

This design ensures a robust, maintainable development environment that supports the high-quality implementation of mypylogger v0.2.0 while maintaining focus on simplicity and reliability.