# Configuration and Logging

This application uses a flexible configuration system that supports YAML files and environment variable overrides. It also features a structured logging setup.

## Configuration

The configuration is loaded from a YAML file. By default, the application looks for `config/config.yaml`. You can specify a different configuration file using the `-config` CLI flag.

```bash
./app -config /path/to/my-config.yaml
```

### Configuration Structure

The configuration file supports the following structure:

```yaml
# Logging configuration
logging:
  # Log Level: debug, info, warn, error
  level: "info"

# Server configuration
server:
  host: "localhost"
  port: 8080
```

### Environment Variables

All configuration values can be overridden using environment variables. The application uses the `APP_` prefix for all environment variables. The variable name is constructed by capitalizing the path to the configuration value and replacing dots/nesting with underscores.

| YAML Path | Environment Variable | Description |
| :--- | :--- | :--- |
| `logging.level` | `APP_LOGGING_LEVEL` | Sets the logging level (debug, info, warn, error) |
| `server.host` | `APP_SERVER_HOST` | Sets the server host address |
| `server.port` | `APP_SERVER_PORT` | Sets the server listening port |

**Example:**

To start the application with `debug` logging and listening on port `9090`:

```bash
APP_LOGGING_LEVEL=debug APP_SERVER_PORT=9090 ./app
```

## Logging

The application uses structured logging (JSON format) via the standard library's `log/slog` package.

### Log Levels

The supported log levels are:

*   `debug`: Detailed information for debugging purposes.
*   `info`: General operational events (startup, shutdown, etc.).
*   `warn`: Non-critical errors or potential issues.
*   `error`: Critical errors that require attention.

The log level is configured via the `logging.level` setting in the configuration file or the `APP_LOGGING_LEVEL` environment variable.

### Log Output

Logs are output to `stdout` in JSON format to facilitate parsing by log management systems.

**Example Log Entry:**

```json
{"time":"2023-10-27T10:00:00.123Z","level":"INFO","msg":"Starting application..."}
```