# Architecture Guide

This guide explains the architecture and design decisions of augint-library.

## 🏗️ System Architecture

```mermaid
graph TB
    subgraph "Package Structure"
        A[src/augint_library] --> B[Core Modules]
        A --> C[CLI Module]
        A --> D[Exceptions]
        A --> E[Protocols]

        B --> F[core.py]
        B --> G[logging.py]
        B --> H[resilience.py]
        B --> I[feature_flags.py]
    end

    subgraph "External Interfaces"
        C --> J[Click CLI]
        E --> K[Type System]
        D --> L[Error Handling]
    end

    subgraph "Optional Features"
        M[Telemetry]
        N[AWS Integration]
        O[Docker Support]
    end

    A -.-> M
    A -.-> N
    A -.-> O

    style A fill:#e3f2fd
    style C fill:#f3e5f5
    style M fill:#fff3e0
```

## 📦 Package Structure

```
augint-library/
├── src/
│   └── augint_library/          # Main package
│       ├── __init__.py          # Public API exports
│       ├── core.py              # Core functionality
│       ├── cli.py               # CLI interface
│       ├── exceptions.py        # Exception hierarchy
│       ├── feature_flags.py     # Feature flag system
│       ├── logging.py           # Logging configuration
│       ├── protocols.py         # Type protocols
│       ├── resilience.py        # Retry/circuit breaker
│       └── telemetry.py         # Usage tracking
├── tests/
│   ├── unit/                    # Unit tests
│   ├── integration/             # Integration tests
│   └── conftest.py             # Shared fixtures
├── docs/                        # API documentation
├── guides/                      # User guides
└── scripts/                     # Setup scripts
```

## 🎯 Design Principles

### 1. Separation of Concerns

```mermaid
graph LR
    A[User Input] --> B[CLI Layer]
    B --> C[Business Logic]
    C --> D[Data Layer]

    B -.-> E[Validation]
    C -.-> F[Error Handling]
    D -.-> G[Persistence]

    style B fill:#e3f2fd
    style C fill:#f3e5f5
    style F fill:#fff3e0
```

**Key Points:**
- CLI is a thin wrapper around library functions
- Business logic is independent of I/O
- Each module has a single responsibility
- Dependencies flow inward (clean architecture)

### 2. Error Handling Strategy

```python
# Hierarchical exception design
AugintError (base)
├── ValidationError      # Input validation failures
├── ConfigurationError   # Config/setup issues
├── ResourceError       # Resource-related errors
│   ├── ResourceNotFoundError
│   └── ResourceAlreadyExistsError
└── NetworkError        # Network/external service
    └── NetworkTimeoutError
```

### 3. Type Safety

We use Python's type system extensively:

```python
# Protocols for flexibility
from typing import Protocol

class DataProcessor(Protocol):
    def process(self, data: Any) -> Any: ...

# Generic types for reusability  
T = TypeVar('T')
class Container(Generic[T]):
    def __init__(self, items: list[T]): ...
```

### 4. Configuration Management

```mermaid
graph TD
    A[Environment Variables] --> D[Config Object]
    B[Config Files] --> D
    C[CLI Arguments] --> D
    D --> E[Application]

    style A fill:#e3f2fd
    style D fill:#f3e5f5
    style E fill:#e8f5e9
```

Priority order (highest to lowest):
1. CLI arguments
2. Environment variables
3. Config files
4. Default values

## 🔌 Extension Points

### Plugin System

```mermaid
graph LR
    A[Plugin Interface] --> B[Plugin A]
    A --> C[Plugin B]
    A --> D[Plugin C]

    E[Plugin Registry] --> A
    F[Application] --> E

    style A fill:#f3e5f5
    style E fill:#fff3e0
```

Plugins can extend:
- Data processors
- Output formatters
- Validation rules
- Storage backends

### Feature Flags

```mermaid
graph TD
    A[Feature Flag Config] --> B{Flag Enabled?}
    B -->|Yes| C[New Implementation]
    B -->|No| D[Old Implementation]

    E[User Context] --> B
    F[Environment] --> B

    style B fill:#fff3e0
    style C fill:#e8f5e9
```

Use cases:
- Gradual rollouts
- A/B testing
- Emergency kill switches
- Beta features

## 🛡️ Security Architecture

### Defense in Depth

```mermaid
graph TB
    A[Input Validation] --> B[Type Checking]
    B --> C[Business Logic]
    C --> D[Output Encoding]

    E[Authentication] --> C
    F[Authorization] --> C
    G[Audit Logging] --> C

    style A fill:#ffebee
    style E fill:#ffebee
    style G fill:#e8f5e9
```

Security measures:
1. **Input validation** - All external input is validated
2. **Type safety** - Mypy catches type errors
3. **Dependency scanning** - Multiple security tools
4. **Secret management** - No hardcoded secrets
5. **Audit trail** - Structured logging

## 🚀 Performance Considerations

### Optimization Strategy

```mermaid
graph LR
    A[Measure] --> B[Profile]
    B --> C[Optimize]
    C --> D[Validate]
    D --> A

    style A fill:#e3f2fd
    style C fill:#f3e5f5
```

Guidelines:
- Profile before optimizing
- Cache expensive operations
- Use generators for large datasets
- Async for I/O-bound operations
- Consider memory vs CPU tradeoffs

### Caching Strategy

```python
from functools import lru_cache

@lru_cache(maxsize=128)
def expensive_operation(param: str) -> Result:
    """Cached for repeated calls."""
    pass

# Time-based cache
from datetime import datetime, timedelta

class CachedResult:
    def __init__(self, ttl: timedelta):
        self.ttl = ttl
        self._cache = {}
        self._timestamps = {}
```

## 📊 Monitoring & Observability

### Telemetry Architecture

```mermaid
graph TD
    A[Application] --> B[Telemetry Client]
    B --> C{Enabled?}
    C -->|Yes| D[Anonymous Events]
    C -->|No| E[No-op]

    D --> F[Sentry]
    F --> G[Dashboards]

    style C fill:#fff3e0
    style E fill:#ffebee
    style G fill:#e8f5e9
```

What we track (when enabled):
- Command usage (anonymized)
- Error rates
- Performance metrics
- Python/OS versions

What we DON'T track:
- Personal information
- File contents
- Network locations
- Sensitive data

## 🔄 CI/CD Architecture

### Pipeline Flow

```mermaid
graph LR
    A[Push] --> B[Pre-commit]
    B --> C[CI Pipeline]
    C --> D[Matrix Tests]
    C --> E[Security Scans]
    C --> F[Coverage]

    D & E & F --> G{Pass?}
    G -->|Yes| H[Build]
    H --> I[Publish]

    G -->|No| J[Fail]

    style G fill:#fff3e0
    style I fill:#e8f5e9
    style J fill:#ffebee
```

### Deployment Strategy

1. **Development** - Every push to feature branch
2. **Staging** - Merges to `main`
3. **Production** - Tagged releases
4. **Rollback** - Revert to previous tag

## 📚 Further Reading

- [Design Patterns](./design-patterns.md)
- [API Guidelines](./api-guidelines.md)
- [Security Best Practices](./security.md)
- [Performance Tuning](./performance.md)
