feat(skel): config loader with YAML + SMARTMUSIC_* env overlay

internal/config/config.go

@@ -0,0 +1,67 @@
+package config
+
+import (
+	"fmt"
+	"os"
+	"strings"
+
+	"gopkg.in/yaml.v3"
+)
+
+type Config struct {
+	Server   ServerConfig   `yaml:"server"`
+	Database DatabaseConfig `yaml:"database"`
+	Log      LogConfig      `yaml:"log"`
+}
+
+type ServerConfig struct {
+	Address string `yaml:"address"`
+}
+
+type DatabaseConfig struct {
+	URL string `yaml:"url"`
+}
+
+type LogConfig struct {
+	Level  string `yaml:"level"`
+	Format string `yaml:"format"`
+}
+
+func Default() Config {
+	return Config{
+		Server:   ServerConfig{Address: ":4533"},
+		Database: DatabaseConfig{URL: ""},
+		Log:      LogConfig{Level: "info", Format: "text"},
+	}
+}
+
+func Load(path string) (Config, error) {
+	cfg := Default()
+	if path != "" {
+		data, err := os.ReadFile(path)
+		if err != nil {
+			if !os.IsNotExist(err) {
+				return cfg, fmt.Errorf("read config %q: %w", path, err)
+			}
+		} else if err := yaml.Unmarshal(data, &cfg); err != nil {
+			return cfg, fmt.Errorf("parse config %q: %w", path, err)
+		}
+	}
+	applyEnv(&cfg)
+	return cfg, nil
+}
+
+func applyEnv(cfg *Config) {
+	if v, ok := os.LookupEnv("SMARTMUSIC_SERVER_ADDRESS"); ok {
+		cfg.Server.Address = v
+	}
+	if v, ok := os.LookupEnv("SMARTMUSIC_DATABASE_URL"); ok {
+		cfg.Database.URL = v
+	}
+	if v, ok := os.LookupEnv("SMARTMUSIC_LOG_LEVEL"); ok {
+		cfg.Log.Level = strings.ToLower(v)
+	}
+	if v, ok := os.LookupEnv("SMARTMUSIC_LOG_FORMAT"); ok {
+		cfg.Log.Format = strings.ToLower(v)
+	}
+}