# Component: ServiceHost

## Purpose

The entry point and lifecycle manager for the LmxProxy Windows service. Handles Topshelf service hosting, Serilog logging setup, component initialization/teardown ordering, and Windows SCM service recovery configuration.

## Location

- `src/ZB.MOM.WW.LmxProxy.Host/Program.cs` — entry point, Serilog setup, Topshelf configuration.
- `src/ZB.MOM.WW.LmxProxy.Host/LmxProxyService.cs` — service lifecycle (Start, Stop, Pause, Continue, Shutdown).

## Responsibilities

- Configure and launch the Topshelf Windows service.
- Load and validate configuration from `appsettings.json`.
- Initialize Serilog logging.
- Orchestrate service startup: create all components in dependency order, connect to MxAccess, start servers.
- Orchestrate service shutdown: stop servers, dispose all components in reverse order.
- Configure Windows SCM service recovery policies.

## 1. Entry Point (Program.cs)

1. Builds configuration from `appsettings.json` + environment variables via `ConfigurationBuilder`.
2. Configures Serilog from the `Serilog` section of appsettings (console + file sinks).
3. Validates configuration using `ConfigurationValidator.ValidateAndLog()`.
4. Configures Topshelf `HostFactory`:
   - Service name: `ZB.MOM.WW.LmxProxy.Host`
   - Display name: `SCADA Bridge LMX Proxy`
   - Start automatically on boot.
   - Service recovery: first failure 1 min, second 5 min, subsequent 10 min, reset period 1 day.
5. Runs the Topshelf host (blocks until service stops).

## 2. Service Lifecycle (LmxProxyService)

### 2.1 Startup Sequence (Start)

Components are created and started in dependency order:

1. Validate configuration.
2. Check/generate TLS certificates (if TLS enabled).
3. Create `PerformanceMetrics`.
4. Create `ApiKeyService` — loads API keys from file.
5. Create `MxAccessClient` via factory.
6. Subscribe to connection state changes.
7. Connect to MxAccess synchronously — times out at `ConnectionTimeoutSeconds` (default 30s).
8. Start `MonitorConnectionAsync` (if `AutoReconnect` enabled).
9. Create `SubscriptionManager`.
10. Create `SessionManager`.
11. Create `HealthCheckService` + `DetailedHealthCheckService`.
12. Create `StatusReportService` + `StatusWebServer`.
13. Create `ScadaGrpcService`.
14. Create `ApiKeyInterceptor`.
15. Configure gRPC `Server` with TLS or insecure credentials.
16. Start gRPC server on `0.0.0.0:{GrpcPort}`.
17. Start `StatusWebServer`.

### 2.2 Shutdown Sequence (Stop)

Components are stopped and disposed in reverse order:

1. Cancel reconnect monitor — wait **5 seconds** for exit.
2. Graceful gRPC server shutdown — **10-second** timeout, then kill.
3. Stop StatusWebServer — **5-second** wait.
4. Dispose all components in reverse creation order.
5. Disconnect from MxAccess — **10-second** timeout.

### 2.3 Other Lifecycle Events

- **Pause**: Supported by Topshelf but behavior is a no-op beyond logging.
- **Continue**: Resume from pause, no-op beyond logging.
- **Shutdown**: System shutdown signal, triggers the same shutdown sequence as Stop.

## 3. Service Recovery (Windows SCM)

Configured via Topshelf's `EnableServiceRecovery`:

| Failure | Action | Delay |
|---------|--------|-------|
| First | Restart service | 1 minute |
| Second | Restart service | 5 minutes |
| Subsequent | Restart service | 10 minutes |
| Reset period | — | 1 day |

All values are configurable via `ServiceRecoveryConfiguration`.

## 4. Service Identity

| Property | Value |
|----------|-------|
| Service name | `ZB.MOM.WW.LmxProxy.Host` |
| Display name | `SCADA Bridge LMX Proxy` |
| Start mode | Automatic |
| Platform | x86 (.NET Framework 4.8) |
| Framework | Topshelf |

## Dependencies

- **Topshelf** — Windows service framework.
- **Serilog** — structured logging (console + file sinks).
- **Microsoft.Extensions.Configuration** — configuration loading.
- **Configuration** — validated configuration objects.
- All other components are created and managed by LmxProxyService.

## Interactions

- **Configuration** is loaded and validated first; all other components receive their settings from it.
- **MxAccessClient** is connected synchronously during startup. If connection fails within the timeout, the service fails to start.
- **GrpcServer** and **StatusWebServer** are started last, after all dependencies are ready.