# Data Models

## Configuration Model

```mermaid
classDiagram
    class Config {
        +Server ServerConfig
        +Metrics MetricsConfig
    }
    class ServerConfig {
        +int Port
        +TLSConfig TLS
    }
    class TLSConfig {
        +bool Enabled
        +string CertFile
        +string KeyFile
    }
    class MetricsConfig {
        +bool Enabled
        +int Port
    }

    Config --> ServerConfig
    Config --> MetricsConfig
    ServerConfig --> TLSConfig
```

### Config Struct Definition

```go
type Config struct {
    Server struct {
        Port int    `yaml:"port"`
        TLS  struct {
            Enabled  bool   `yaml:"enabled"`
            CertFile string `yaml:"cert_file"`
            KeyFile  string `yaml:"key_file"`
        } `yaml:"tls"`
    } `yaml:"server"`
    Metrics struct {
        Enabled bool `yaml:"enabled"`
        Port    int  `yaml:"port"`
    } `yaml:"metrics"`
}
```

### Default Configuration Values

| Field | Default | Notes |
|-------|---------|-------|
| `server.port` | 8443 | Standard alternate HTTPS port |
| `server.tls.enabled` | false (config.yaml) / true (example) | Toggle TLS |
| `server.tls.cert_file` | `cert.pem` | Relative to working directory |
| `server.tls.key_file` | `key.pem` | Relative to working directory |
| `metrics.enabled` | true | Prometheus metrics |
| `metrics.port` | 9090 | Standard Prometheus port |

---

## Hub State Model

```mermaid
classDiagram
    class Hub {
        -map~*websocket.Conn, bool~ clients
        -chan []byte broadcast
        -chan *websocket.Conn register
        -chan *websocket.Conn unregister
        -sync.RWMutex mu
        +New() Hub
        +Run()
        +HandleWebSocket(w, r)
        +ClientCount() int
    }
```

### Channel Types

| Channel | Direction | Payload | Buffer |
|---------|-----------|---------|--------|
| `register` | Handler → Hub | `*websocket.Conn` | Unbuffered |
| `unregister` | Reader → Hub | `*websocket.Conn` | Unbuffered |
| `broadcast` | Reader → Hub | `[]byte` | Unbuffered |

---

## Message Model

The relay server does **not** impose any message structure. Messages are raw `[]byte` payloads passed through as WebSocket text frames.

```mermaid
graph LR
    A[Client A sends bytes] --> B[Hub broadcast channel]
    B --> C[Written as TextMessage to all clients]
```

The example HTML client uses an informal format:
```
{name}<br>{message_text}
```

But this is purely client-side convention — the server is format-agnostic.

---

## Metrics Model

```mermaid
classDiagram
    class PrometheusMetrics {
        +Gauge ConnectedClients
        +Gauge MessagesTotal
        +Gauge ConnectionsTotal
        +Gauge DisconnectionsTotal
    }
```

| Metric | Update Trigger |
|--------|---------------|
| `ConnectedClients` | Set on register/unregister (absolute count) |
| `MessagesTotal` | Incremented on each broadcast |
| `ConnectionsTotal` | Incremented on register |
| `DisconnectionsTotal` | Incremented on unregister |

---

## Connection State Machine

```mermaid
stateDiagram-v2
    [*] --> Connecting: HTTP request to /
    Connecting --> Connected: WebSocket upgrade success
    Connecting --> Failed: Upgrade error
    Connected --> Active: Registered in Hub
    Active --> Active: Sending/Receiving messages
    Active --> Disconnecting: Read error or client close
    Disconnecting --> Closed: Unregistered from Hub
    Failed --> [*]
    Closed --> [*]
```