# Backend Architecture Restructuring

## Overview

The backend has been restructured from a monolithic approach to a clean **3-layer architecture** with proper separation of concerns.

## Architecture Layers

### 1. Infrastructure Layer (`layers/infrastructure/`)
**Responsibility**: Data access, external services, and low-level operations

- **`database_connection.py`** - MongoDB connection management and indexing
- **`redis_connection.py`** - Redis connection and basic operations  
- **`repositories.py`** - Data access layer with repository pattern

**Key Principles**:
- No business logic
- Only handles data persistence and retrieval
- Provides abstractions for external services

### 2. Business Layer (`layers/business/`)
**Responsibility**: Business logic, data processing, and core application rules

- **`sensor_service.py`** - Sensor data processing and validation
- **`room_service.py`** - Room metrics calculation and aggregation
- **`analytics_service.py`** - Analytics calculations and reporting
- **`cleanup_service.py`** - Data retention and maintenance

**Key Principles**:
- Contains all business rules and validation
- Independent of presentation concerns
- Uses infrastructure layer for data access

### 3. Presentation Layer (`layers/presentation/`)
**Responsibility**: HTTP endpoints, WebSocket handling, and user interface

- **`api_routes.py`** - REST API endpoints and request/response handling
- **`websocket_handler.py`** - WebSocket connection management
- **`redis_subscriber.py`** - Real-time data broadcasting

**Key Principles**:
- Handles HTTP requests and responses
- Manages real-time communications
- Delegates business logic to business layer

## File Comparison

### Before (Monolithic)
```
main.py (203 lines)           # Mixed concerns
api.py (506 lines)           # API + some business logic  
database.py (220 lines)      # DB + Redis + cleanup
persistence.py (448 lines)   # Business + data access
models.py (236 lines)        # Data models
```

### After (Layered)
```
Infrastructure Layer:
├── database_connection.py (114 lines)    # Pure DB connection
├── redis_connection.py (89 lines)       # Pure Redis connection  
└── repositories.py (376 lines)          # Clean data access

Business Layer:
├── sensor_service.py (380 lines)        # Sensor business logic
├── room_service.py (242 lines)         # Room business logic
├── analytics_service.py (333 lines)     # Analytics business logic
└── cleanup_service.py (278 lines)       # Cleanup business logic

Presentation Layer:
├── api_routes.py (430 lines)           # Pure API endpoints
├── websocket_handler.py (103 lines)    # WebSocket management
└── redis_subscriber.py (148 lines)     # Real-time broadcasting

Core:
├── main_layered.py (272 lines)         # Clean application entry
└── models.py (236 lines)               # Unchanged data models
```

## Key Improvements

### 1. **Separation of Concerns**
- Each layer has a single, well-defined responsibility
- Infrastructure concerns isolated from business logic
- Business logic separated from presentation

### 2. **Testability**
- Each layer can be tested independently
- Business logic testable without database dependencies
- Infrastructure layer testable without business complexity

### 3. **Maintainability**
- Changes in one layer don't affect others
- Clear boundaries make code easier to understand
- Reduced coupling between components

### 4. **Scalability**
- Layers can be scaled independently
- Easy to replace implementations within layers
- Clear extension points for new features

### 5. **Dependency Management**
- Clear dependency flow: Presentation → Business → Infrastructure
- No circular dependencies
- Infrastructure layer has no knowledge of business rules

## Usage

### Running the Layered Application
```bash
# Use the new layered main file
conda activate dashboard
uvicorn main_layered:app --reload
```

### Testing the Structure
```bash
# Validate the architecture
python test_structure.py
```

## Benefits Achieved

✅ **Clear separation of concerns**  
✅ **Infrastructure isolated from business logic**  
✅ **Business logic separated from presentation**  
✅ **Easy to test individual layers**  
✅ **Maintainable and scalable structure**  
✅ **No layering violations detected**  
✅ **2,290+ lines properly organized across 10+ files**  

## Migration Path

The original files are preserved, so you can:
1. Test the new layered architecture with `main_layered.py`
2. Gradually migrate consumers to use the new structure
3. Remove old files once confident in the new architecture

Both architectures can coexist during the transition period.