feat(config): support cli config path and nested config

Adds -config CLI flag to main.go. Moves ParseLogLevel to internal/config. Adds ServerConfig nested struct to Config and corresponding tests for yaml/env overrides.

cmd/app/main.go

@@ -2,11 +2,11 @@ package main
 
 import (
 	"context"
+	"flag"
 	"fmt"
 	"log/slog"
 	"os"
 	"os/signal"
-	"strings"
 	"syscall"
 	"time"
 
@@ -14,8 +14,13 @@ import (
 )
 
 func main() {
+	// Parse CLI flags
+	var configPath string
+	flag.StringVar(&configPath, "config", "config/config.yaml", "path to config file")
+	flag.Parse()
+
 	// Load Configuration
-	cfg, err := config.Load("config/config.yaml", "APP")
+	cfg, err := config.Load(configPath, "APP")
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "failed to load config: %v\n", err)
 		os.Exit(1)
@@ -23,7 +28,7 @@ func main() {
 
 	// Setup Logger
 	opts := &slog.HandlerOptions{
-		Level: parseLogLevel(cfg.LogLevel),
+		Level: config.ParseLogLevel(cfg.LogLevel),
 	}
 	logger := slog.New(slog.NewJSONHandler(os.Stdout, opts))
 	slog.SetDefault(logger)
@@ -46,21 +51,6 @@ func main() {
 	}
 }
 
-func parseLogLevel(level string) slog.Level {
-	switch strings.ToLower(level) {
-	case "debug":
-		return slog.LevelDebug
-	case "info":
-		return slog.LevelInfo
-	case "warn":
-		return slog.LevelWarn
-	case "error":
-		return slog.LevelError
-	default:
-		return slog.LevelInfo
-	}
-}
-
 func run(ctx context.Context) error {
 	slog.Info("Starting application...")