Add initial framework of configuration.

feat: configuration file system of app.

Note: still work in progress.

internal/config/load.go

@@ -0,0 +1,66 @@
+package config
+
+import (
+	"errors"
+	"fmt"
+	"strings"
+
+	"github.com/go-viper/mapstructure/v2"
+	"github.com/spf13/viper"
+)
+
+func defaults(v *viper.Viper) {
+	v.SetDefault("server.host", "0.0.0.0")
+	v.SetDefault("server.port", 10086)
+
+	v.SetDefault("database.driver", "sqlite3")
+	v.SetDefault("database.path", "data/mygo.db")
+
+	v.SetDefault("storage.driver", "local")
+	v.SetDefault("storage.local.path", "data/files")
+
+	v.SetDefault("jwt.secret", "dev-secret-do-not-use-in-production")
+	v.SetDefault("jwt.access_ttl", "15m")
+	v.SetDefault("jwt.refresh_ttl", "168h")
+}
+
+func decodeHook() viper.DecoderConfigOption {
+	return viper.DecodeHook(mapstructure.StringToTimeDurationHookFunc())
+}
+
+func New() *viper.Viper {
+	v := viper.New()
+	v.SetEnvPrefix("MYGO")
+	v.SetEnvKeyReplacer(strings.NewReplacer(".", "_"))
+	v.AutomaticEnv()
+	defaults(v)
+	return v
+}
+
+func Load(v *viper.Viper, cfgFile string) (*Config, error) {
+	if cfgFile != "" {
+		v.SetConfigFile(cfgFile)
+	} else {
+		v.SetConfigName("config")
+		v.SetConfigType("yaml")
+		v.AddConfigPath(".")
+	}
+
+	if err := v.ReadInConfig(); err != nil {
+		var notFound viper.ConfigFileNotFoundError
+		if !errors.As(err, &notFound) {
+			return nil, fmt.Errorf("read config: %w", err)
+		}
+	}
+
+	var cfg Config
+	if err := v.Unmarshal(&cfg, decodeHook()); err != nil {
+		return nil, fmt.Errorf("unmarshal config: %w", err)
+	}
+
+	if err := cfg.Validate(); err != nil {
+		return nil, fmt.Errorf("validate config: %w", err)
+	}
+
+	return &cfg, nil
+}