# Feature: Connection Lifecycle Management

## Description

Manages the lifecycle of SSE (Server-Sent Events) connections including creation, tracking, health monitoring, and graceful closure. Supports multiple concurrent client connections per flight with proper resource management.

## Component APIs Implemented

### `create_stream(flight_id: str, client_id: str) -> StreamConnection`
Establishes a new SSE connection for a client subscribing to a flight's events.

### `close_stream(flight_id: str, client_id: str) -> bool`
Closes an existing SSE connection and cleans up associated resources.

### `get_active_connections(flight_id: str) -> int`
Returns the count of active SSE connections for a given flight.

## External Tools and Services

- **FastAPI/Starlette**: SSE response streaming support
- **asyncio**: Asynchronous connection handling and concurrent stream management

## Internal Methods

| Method | Purpose |
|--------|---------|
| `_register_connection(flight_id, client_id, stream)` | Adds connection to internal registry |
| `_unregister_connection(flight_id, client_id)` | Removes connection from registry |
| `_get_connections_for_flight(flight_id)` | Returns all active streams for a flight |
| `_generate_stream_id()` | Creates unique identifier for stream |
| `_handle_client_disconnect(flight_id, client_id)` | Cleanup on unexpected disconnect |

## Data Structures

```python
# Connection registry: Dict[flight_id, Dict[client_id, StreamConnection]]
# Allows O(1) lookup by flight and client
```

## Unit Tests

| Test | Description |
|------|-------------|
| `test_create_stream_returns_valid_connection` | Verify StreamConnection has all required fields |
| `test_create_stream_unique_stream_ids` | Multiple streams get unique identifiers |
| `test_close_stream_removes_from_registry` | Connection no longer tracked after close |
| `test_close_stream_nonexistent_returns_false` | Graceful handling of invalid close |
| `test_get_active_connections_empty` | Returns 0 when no connections exist |
| `test_get_active_connections_multiple_clients` | Correctly counts concurrent connections |
| `test_multiple_flights_isolated` | Connections for different flights don't interfere |
| `test_same_client_reconnect` | Client can reconnect with same client_id |

## Integration Tests

| Test | Description |
|------|-------------|
| `test_concurrent_client_connections` | 10 clients connect simultaneously to same flight |
| `test_connection_survives_idle_period` | Connection remains open during inactivity |
| `test_client_disconnect_detection` | System detects when client drops connection |
| `test_connection_cleanup_on_flight_completion` | All connections closed when flight ends |

