# Core Client Architecture Implementation Plan

## 📋 **SCOPE & OBJECTIVES**

### **Primary Goals**
- Implement the foundational client architecture for Cognify SDK
- Create robust HTTP client wrapper with sync/async support
- Establish configuration management system
- Implement standardized request/response handling

### **Deliverables**
1. `CognifyClient` base class with configuration
2. HTTP client wrapper using httpx
3. Request/response middleware system
4. Error handling and exception hierarchy
5. Configuration management (env vars, config files)
6. Basic logging and debugging support

## 🛠️ **TECHNOLOGY STACK**

### **Core Dependencies**
- **httpx**: HTTP client with async/sync support
- **pydantic**: Configuration validation and settings
- **typing-extensions**: Enhanced type hints
- **python-dotenv**: Environment variable management

### **Architecture Components**
```python
cognify_sdk/
├── __init__.py              # Main exports
├── client.py               # Core CognifyClient class
├── config.py               # Configuration management
├── http_client.py          # HTTP client wrapper
├── exceptions.py           # Custom exception hierarchy
├── types.py               # Common type definitions
└── utils.py               # Utility functions
```

## 🏗️ **IMPLEMENTATION STRATEGY**

### **Step 1: Configuration System**
```python
# config.py
class CognifyConfig(BaseSettings):
    api_key: Optional[str] = None
    base_url: str = "https://api.cognify.ai"
    timeout: int = 30
    max_retries: int = 3
    debug: bool = False
    
    class Config:
        env_prefix = "COGNIFY_"
        env_file = ".env"
```

### **Step 2: HTTP Client Wrapper**
```python
# http_client.py
class HTTPClient:
    def __init__(self, config: CognifyConfig):
        self.config = config
        self.client = httpx.Client(
            base_url=config.base_url,
            timeout=config.timeout
        )
        self.async_client = httpx.AsyncClient(
            base_url=config.base_url,
            timeout=config.timeout
        )
    
    def request(self, method: str, url: str, **kwargs) -> Response
    async def arequest(self, method: str, url: str, **kwargs) -> Response
```

### **Step 3: Core Client Class**
```python
# client.py
class CognifyClient:
    def __init__(
        self,
        api_key: Optional[str] = None,
        base_url: Optional[str] = None,
        **kwargs
    ):
        self.config = CognifyConfig(
            api_key=api_key,
            base_url=base_url or "https://api.cognify.ai",
            **kwargs
        )
        self.http = HTTPClient(self.config)
        
        # Initialize modules
        self.auth = AuthModule(self)
        self.documents = DocumentsModule(self)
        self.query = QueryModule(self)
        # ... other modules
```

### **Step 4: Exception Hierarchy**
```python
# exceptions.py
class CognifyError(Exception):
    """Base exception for all Cognify SDK errors"""

class CognifyAPIError(CognifyError):
    """API-related errors"""
    def __init__(self, message: str, status_code: int, response: dict):
        self.status_code = status_code
        self.response = response
        super().__init__(message)

class CognifyAuthenticationError(CognifyAPIError):
    """Authentication-related errors"""

class CognifyValidationError(CognifyError):
    """Input validation errors"""
```

## 🔗 **DEPENDENCIES**

### **Prerequisites**
- Python 3.11+ environment
- Understanding of httpx library
- Pydantic v2 knowledge

### **External Dependencies**
- httpx >= 0.25.0
- pydantic >= 2.0.0
- typing-extensions >= 4.0.0
- python-dotenv >= 1.0.0

## ✅ **SUCCESS CRITERIA**

### **Functional Requirements**
- [ ] Client can be instantiated with various configuration options
- [ ] Both sync and async HTTP methods working
- [ ] Configuration loaded from environment variables
- [ ] Proper error handling and custom exceptions
- [ ] Request/response logging for debugging

### **Quality Metrics**
- **Test Coverage**: 95%+ for core client functionality
- **Type Coverage**: 100% type hints
- **Performance**: <10ms overhead per request
- **Memory**: Efficient connection pooling

### **API Design**
```python
# Simple usage
client = CognifyClient(api_key="cog_xxx")
response = client.documents.list()

# Advanced configuration
client = CognifyClient(
    api_key="cog_xxx",
    base_url="https://custom.cognify.ai",
    timeout=60,
    max_retries=5,
    debug=True
)

# Async usage
async with CognifyClient(api_key="cog_xxx") as client:
    response = await client.documents.alist()
```

## ⏱️ **TIMELINE**

### **Day 1: Foundation**
- Setup package structure
- Implement configuration system
- Basic HTTP client wrapper

### **Day 2: Core Client**
- CognifyClient class implementation
- Module initialization system
- Basic error handling

### **Day 3: Testing & Polish**
- Comprehensive test suite
- Documentation and examples
- Performance optimization

## 🧪 **TESTING STRATEGY**

### **Unit Tests**
```python
def test_client_initialization():
    client = CognifyClient(api_key="test_key")
    assert client.config.api_key == "test_key"

def test_http_client_sync():
    # Mock HTTP responses
    # Test sync requests

async def test_http_client_async():
    # Mock HTTP responses  
    # Test async requests

def test_error_handling():
    # Test various error scenarios
    # Verify proper exception types
```

### **Integration Tests**
- Configuration loading from environment
- HTTP client connection handling
- Error response parsing

## 📚 **DOCUMENTATION**

### **API Reference**
- CognifyClient class documentation
- Configuration options reference
- Error handling guide

### **Examples**
```python
# Basic client setup
from cognify_sdk import CognifyClient

client = CognifyClient(api_key="your_api_key")

# Environment-based configuration
# Set COGNIFY_API_KEY=your_key
client = CognifyClient()  # Auto-loads from env

# Custom configuration
client = CognifyClient(
    api_key="your_key",
    base_url="https://custom.api.com",
    timeout=60
)
```

## 🔄 **RISK MITIGATION**

### **Technical Risks**
- **HTTP Client Issues**: Comprehensive error handling
- **Configuration Complexity**: Simple defaults with override options
- **Performance**: Connection pooling and efficient request handling

### **Implementation Risks**
- **API Changes**: Flexible configuration system
- **Backward Compatibility**: Semantic versioning

---

**Plan Status**: 🟡 Ready for Implementation
**Dependencies**: Foundation plan (01) must be started
**Estimated Effort**: 3 days
**Priority**: High (Core Foundation)
