# SkyView Architecture Documentation

## Overview

SkyView is a high-performance, multi-source ADS-B aircraft tracking system built in Go with a modern JavaScript frontend. It connects to multiple dump1090 Beast format receivers, performs intelligent data fusion, and provides low-latency aircraft tracking through a responsive web interface.

## System Architecture

```
┌─────────────────┐    ┌──────────────┐    ┌─────────────────┐
│   dump1090       │    │   dump1090   │    │   dump1090      │
│   Receiver 1     │    │   Receiver 2 │    │   Receiver N    │
│   Port 30005     │    │   Port 30005 │    │   Port 30005    │
└─────────┬───────┘    └──────┬───────┘    └─────────┬───────┘
          │                   │                      │
          │ Beast Binary      │ Beast Binary         │ Beast Binary
          │ TCP Stream        │ TCP Stream           │ TCP Stream
          │                   │                      │
          └───────────────────┼──────────────────────┘
                              │
                    ┌─────────▼──────────┐
                    │   SkyView Server   │
                    │                    │
                    │ ┌────────────────┐ │
                    │ │  Beast Client  │ │ ── Multi-source TCP clients
                    │ │   Manager      │ │
                    │ └────────────────┘ │
                    │ ┌────────────────┐ │
                    │ │  Mode S/ADS-B  │ │ ── Message parsing & decoding
                    │ │    Decoder     │ │
                    │ └────────────────┘ │
                    │ ┌────────────────┐ │
                    │ │  Data Merger   │ │ ── Intelligent data fusion
                    │ │   & ICAO DB    │ │
                    │ └────────────────┘ │
                    │ ┌────────────────┐ │
                    │ │ HTTP/WebSocket │ │ ── Low-latency web interface
                    │ │    Server      │ │
                    │ └────────────────┘ │
                    └─────────┬──────────┘
                              │
                    ┌─────────▼──────────┐
                    │   Web Interface    │
                    │                    │
                    │ • Interactive Maps │
                    │ • Low-latency Updates│
                    │ • Aircraft Details │
                    │ • Coverage Analysis│
                    │ • 3D Visualization │
                    └────────────────────┘
```

## Core Components

### 1. Beast Format Clients (`internal/client/`)

**Purpose**: Manages TCP connections to dump1090 receivers

**Key Features**:
- Concurrent connection handling for multiple sources
- Automatic reconnection with exponential backoff
- Beast binary format parsing
- Per-source connection monitoring and statistics

**Files**:
- `beast.go`: Main client implementation

### 2. Mode S/ADS-B Decoder (`internal/modes/`)

**Purpose**: Decodes raw Mode S and ADS-B messages into structured aircraft data

**Key Features**:
- CPR (Compact Position Reporting) decoding with zone ambiguity resolution
- ADS-B message type parsing (position, velocity, identification)
- Aircraft category and type classification
- Signal quality assessment

**Files**:
- `decoder.go`: Core decoding logic

### 3. Data Merger (`internal/merger/`)

**Purpose**: Fuses aircraft data from multiple sources using intelligent conflict resolution

**Key Features**:
- Signal strength-based source selection
- High-performance data fusion and conflict resolution
- Aircraft state management and lifecycle tracking
- Historical data collection (position, altitude, speed, signal trails)
- Automatic stale aircraft cleanup

**Files**:
- `merger.go`: Multi-source data fusion engine

### 4. ICAO Country Database (`internal/icao/`)

**Purpose**: Provides comprehensive ICAO address to country mapping

**Key Features**:
- In-memory database with 100+ allocations covering 70+ countries and territories
- Based on official aerotransport.org ICAO allocation tables
- Fast binary search lookups on sorted allocation ranges
- Complete country names, ISO codes, and flag emojis
- Zero external dependencies - pure Go implementation

**Files**:
- `database.go`: In-memory ICAO allocation database with binary search

### 5. HTTP/WebSocket Server (`internal/server/`)

**Purpose**: Serves web interface and provides low-latency data streaming

**Key Features**:
- RESTful API for aircraft and system data
- WebSocket connections for low-latency updates
- Static asset serving with embedded resources
- Coverage analysis and signal heatmaps

**Files**:
- `server.go`: HTTP server and WebSocket handler

### 6. Web Frontend (`assets/static/`)

**Purpose**: Interactive web interface for aircraft tracking and visualization

**Key Technologies**:
- **Leaflet.js**: Interactive maps and aircraft markers
- **Three.js**: 3D radar visualization
- **Chart.js**: Live statistics and charts
- **WebSockets**: Live data streaming
- **Responsive CSS**: Mobile-optimized interface

**Files**:
- `index.html`: Main web interface
- `js/app.js`: Main application orchestrator
- `js/modules/`: Modular JavaScript components
  - `aircraft-manager.js`: Aircraft marker and trail management
  - `map-manager.js`: Map controls and overlays
  - `ui-manager.js`: User interface state management
  - `websocket.js`: Low-latency data connections
- `css/style.css`: Responsive styling and themes
- `icons/`: SVG aircraft type icons

## Data Flow

### 1. Data Ingestion
1. **Beast Clients** connect to dump1090 receivers via TCP
2. **Beast Parser** processes binary message stream
3. **Mode S Decoder** converts raw messages to structured aircraft data
4. **Data Merger** receives aircraft updates with source attribution

### 2. Data Fusion
1. **Signal Analysis**: Compare signal strength across sources
2. **Conflict Resolution**: Select best data based on signal quality and recency
3. **State Management**: Update aircraft position, velocity, and metadata
4. **History Tracking**: Maintain trails for visualization

### 3. Country Lookup
1. **ICAO Extraction**: Extract 24-bit ICAO address from aircraft data
2. **Database Query**: Lookup country information in in-memory database using binary search
3. **Data Enrichment**: Add country, country code, and flag to aircraft state

### 4. Data Distribution
1. **REST API**: Provide aircraft data via HTTP endpoints
2. **WebSocket Streaming**: Push low-latency updates to connected clients
3. **Frontend Processing**: Update maps, tables, and visualizations
4. **User Interface**: Display aircraft with country flags and details

## Configuration System

### Configuration Sources (Priority Order)
1. Command-line flags (highest priority)
2. Configuration file (JSON)
3. Default values (lowest priority)

### Configuration Structure
```json
{
  "server": {
    "host": "",        // Bind address (empty = all interfaces)
    "port": 8080       // HTTP server port
  },
  "sources": [
    {
      "id": "unique-id",      // Source identifier
      "name": "Display Name", // Human-readable name
      "host": "hostname",     // Receiver hostname/IP
      "port": 30005,          // Beast format port
      "latitude": 51.4700,    // Receiver location
      "longitude": -0.4600,   
      "altitude": 50.0,       // Meters above sea level
      "enabled": true         // Source enable/disable
    }
  ],
  "settings": {
    "history_limit": 500,    // Max trail points per aircraft
    "stale_timeout": 60,     // Seconds before aircraft removed
    "update_rate": 1         // WebSocket update frequency
  },
  "origin": {
    "latitude": 51.4700,     // Map center point
    "longitude": -0.4600,
    "name": "Origin Name"
  }
}
```

## Performance Characteristics

### Concurrency Model
- **Goroutine per Source**: Each Beast client runs in separate goroutine
- **Mutex-Protected Merger**: Thread-safe aircraft state management
- **WebSocket Broadcasting**: Concurrent client update distribution
- **Non-blocking I/O**: Asynchronous network operations

### Memory Management
- **Bounded History**: Configurable limits on historical data storage
- **Automatic Cleanup**: Stale aircraft removal to prevent memory leaks
- **Efficient Data Structures**: Maps for O(1) aircraft lookups
- **Embedded Assets**: Static files bundled in binary

### Scalability
- **Multi-source Support**: Tested with 10+ concurrent receivers
- **High Message Throughput**: Handles 1000+ messages/second per source
- **Low-latency Updates**: Sub-second latency for aircraft updates
- **Responsive Web UI**: Optimized for 100+ concurrent aircraft

## Security Considerations

### Network Security
- **No Authentication Required**: Designed for trusted network environments
- **Local Network Operation**: Intended for private receiver networks
- **WebSocket Origin Checking**: Basic CORS protection

### System Security
- **Unprivileged Execution**: Runs as non-root user in production
- **Filesystem Isolation**: Minimal file system access required
- **Network Isolation**: Only requires outbound TCP to receivers
- **Systemd Hardening**: Security features enabled in service file

### Data Privacy
- **Public ADS-B Data**: Only processes publicly broadcast aircraft data
- **No Personal Information**: Aircraft tracking only, no passenger data
- **Local Processing**: No data transmitted to external services
- **Historical Limits**: Configurable data retention periods

## External Resources

### Official Standards
- **ICAO Document 8585**: Designators for Aircraft Operating Agencies
- **RTCA DO-260B**: ADS-B Message Formats and Protocols
- **ITU-R M.1371-5**: Technical characteristics for universal ADS-B

### Technology Dependencies
- **Go Language**: https://golang.org/
- **Leaflet.js**: https://leafletjs.com/ - Interactive maps
- **Three.js**: https://threejs.org/ - 3D visualization
- **Chart.js**: https://www.chartjs.org/ - Statistics charts
- **WebSocket Protocol**: RFC 6455

### ADS-B Ecosystem
- **dump1090**: https://github.com/antirez/dump1090 - SDR ADS-B decoder
- **Beast Binary Format**: Mode S data interchange format
- **FlightAware**: ADS-B network and data provider
- **OpenSky Network**: Research-oriented ADS-B network

## Development Guidelines

### Code Organization
- **Package per Component**: Clear separation of concerns
- **Interface Abstractions**: Testable and mockable components
- **Error Handling**: Comprehensive error reporting and recovery
- **Documentation**: Extensive code comments and examples

### Testing Strategy
- **Unit Tests**: Component-level testing with mocks
- **Integration Tests**: End-to-end data flow validation
- **Performance Tests**: Load testing with simulated data
- **Manual Testing**: Real-world receiver validation

### Deployment Options
- **Standalone Binary**: Single executable with embedded assets
- **Debian Package**: Systemd service with configuration
- **Docker Container**: Containerized deployment option
- **Development Mode**: Hot-reload for frontend development

---

**SkyView Architecture** - Designed for reliability, performance, and extensibility in multi-source ADS-B tracking applications.