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...")
 

internal/config/config.go

@@ -2,6 +2,7 @@ package config
 
 import (
 	"fmt"
+	"log/slog"
 	"os"
 	"reflect"
 	"strconv"
@@ -13,7 +14,14 @@ import (
 
 // Config holds the application configuration.
 type Config struct {
-	LogLevel string `yaml:"log_level"`
+	LogLevel string       `yaml:"log_level"`
+	Server   ServerConfig `yaml:"server"`
+}
+
+// ServerConfig holds server-specific configuration.
+type ServerConfig struct {
+	Host string `yaml:"host"`
+	Port int    `yaml:"port"`
 }
 
 // Load reads configuration from a YAML file and overrides it with environment variables.
@@ -42,6 +50,22 @@ func Load(configPath string, envPrefix string) (*Config, error) {
 	return cfg, nil
 }
 
+// ParseLogLevel converts a string log level to a slog.Level.
+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
+	}
+}
+
 // overrideFromEnv uses reflection to traverse the struct and update fields from env vars.
 func overrideFromEnv(cfg interface{}, prefix string) error {
 	v := reflect.ValueOf(cfg)

internal/config/config_test.go

@@ -1,6 +1,7 @@
 package config
 
 import (
+	"log/slog"
 	"os"
 	"path/filepath"
 	"testing"
@@ -13,6 +14,9 @@ func TestLoad(t *testing.T) {
 	
 	yamlContent := []byte(`
 log_level: "info"
+server:
+  host: "localhost"
+  port: 8080
 `)
 	if err := os.WriteFile(configFile, yamlContent, 0644); err != nil {
 		t.Fatalf("failed to write temp config file: %v", err)
@@ -26,11 +30,23 @@ log_level: "info"
 		if cfg.LogLevel != "info" {
 			t.Errorf("expected LogLevel 'info', got '%s'", cfg.LogLevel)
 		}
+		if cfg.Server.Host != "localhost" {
+			t.Errorf("expected Server.Host 'localhost', got '%s'", cfg.Server.Host)
+		}
+		if cfg.Server.Port != 8080 {
+			t.Errorf("expected Server.Port 8080, got %d", cfg.Server.Port)
+		}
 	})
 
 	t.Run("Override from Env", func(t *testing.T) {
 		os.Setenv("TEST_LOG_LEVEL", "debug")
-		defer os.Unsetenv("TEST_LOG_LEVEL")
+		os.Setenv("TEST_SERVER_PORT", "9090")
+		os.Setenv("TEST_SERVER_HOST", "0.0.0.0")
+		defer func() {
+			os.Unsetenv("TEST_LOG_LEVEL")
+			os.Unsetenv("TEST_SERVER_PORT")
+			os.Unsetenv("TEST_SERVER_HOST")
+		}()
 
 		cfg, err := Load(configFile, "TEST")
 		if err != nil {
@@ -39,5 +55,34 @@ log_level: "info"
 		if cfg.LogLevel != "debug" {
 			t.Errorf("expected LogLevel 'debug', got '%s'", cfg.LogLevel)
 		}
+		if cfg.Server.Port != 9090 {
+			t.Errorf("expected Server.Port 9090, got %d", cfg.Server.Port)
+		}
+		if cfg.Server.Host != "0.0.0.0" {
+			t.Errorf("expected Server.Host '0.0.0.0', got '%s'", cfg.Server.Host)
+		}
 	})
 }
+
+func TestParseLogLevel(t *testing.T) {
+	tests := []struct {
+		input    string
+		expected slog.Level
+	}{
+		{"debug", slog.LevelDebug},
+		{"DEBUG", slog.LevelDebug},
+		{"info", slog.LevelInfo},
+		{"warn", slog.LevelWarn},
+		{"error", slog.LevelError},
+		{"unknown", slog.LevelInfo},
+		{"", slog.LevelInfo},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.input, func(t *testing.T) {
+			if got := ParseLogLevel(tt.input); got != tt.expected {
+				t.Errorf("ParseLogLevel(%q) = %v, want %v", tt.input, got, tt.expected)
+			}
+		})
+	}
+}