# Architecture

This document provides an overview of the Catalog application architecture for developers.

## Technology Stack

### Frontend

Catalog is built using Flutter for cross-platform development:

- **Framework**: Flutter 3.x
- **Language**: Dart
- **State Management**: Provider/Riverpod
- **HTTP Client**: Dio
- **Local Storage**: SharedPreferences, SQLite

### Platforms

The application targets multiple platforms from a single codebase:

- **Web**: Flutter Web compiled to JavaScript
- **iOS**: Native iOS application
- **Android**: Native Android application
- **Desktop**: Windows, macOS, Linux via Flutter desktop

## Project Structure

```
Catalog/
├── lib/
│   ├── main.dart           # Application entry point
│   ├── models/             # Data models
│   ├── services/           # API and business logic
│   ├── providers/          # State management
│   ├── screens/            # UI screens
│   ├── widgets/            # Reusable widgets
│   └── utils/              # Utilities and helpers
├── assets/                 # Static assets (images, fonts)
├── config/                 # Configuration files
├── test/                   # Unit and widget tests
└── docs/                   # Documentation (you are here)
```

## Key Components

### Services Layer

Services handle external communication and business logic:

- **API Service**: HTTP communication with backend services
- **Auth Service**: Authentication and session management
- **Search Service**: Search query handling and result processing
- **Cache Service**: Local caching for offline support

### State Management

Application state is managed through:

- **Providers**: Dependency injection and state containers
- **Notifiers**: Reactive state updates
- **Selectors**: Computed/derived state

### Data Flow

```
User Action → Provider → Service → API
                ↓
            State Update
                ↓
            UI Rebuild
```

## Backend Integration

### API Communication

Catalog communicates with backend services via:

- REST APIs for CRUD operations
- WebSockets for real-time updates
- GraphQL for complex queries (where applicable)

### Authentication

Authentication flow:

1. User enters credentials
2. Auth service validates with backend
3. JWT token stored securely
4. Token included in subsequent requests
5. Token refresh handled automatically

## Build & Deployment

### Build Environments

- **Local**: Development builds with debug tools
- **Development**: Deployed to dev environment
- **QA**: Quality assurance testing
- **Staging**: Pre-production verification
- **Production**: Live deployment

### CI/CD Pipeline

Automated deployment via GitHub Actions:

1. Code pushed to branch
2. Build triggered
3. Tests executed
4. Docker image created
5. Deployed to target environment

## Configuration

### Environment Configuration

Environment-specific settings in `config/`:

- API endpoints
- Feature flags
- Logging levels
- Analytics configuration

### Runtime Configuration

Some settings configurable at runtime:

- User preferences
- Theme settings
- Cache policies