setting.go

package setting

import (
	"log"
	"os"
	"reflect"
)

// Load ...
func Load(config interface{}) {
	// TODO, ensure config is struct

	v := reflect.ValueOf(config).Elem()
	t := v.Type()

	loadStruct(t, v)
}

func loadStruct(t reflect.Type, v reflect.Value) {
	for i := 0; i < v.NumField(); i++ {
		tt := t.Field(i)
		vv := v.Field(i)
		if vv.Kind() == reflect.Struct {
			loadStruct(tt.Type, vv)
		} else {
			set(tt, vv)
		}
	}
}

func set(field reflect.StructField, value reflect.Value) {
	// TODO, ensure value is set-able

	s := getString(field)

	// Set value based on type
	// TODO, handle more than strings!
	switch value.Kind() {
	case reflect.String:
		value.SetString(s)
	default:
		// TODO, error instead of logging
		log.Printf("%v field of type '%v' cannot be set. Defaulting to zero value",
			field.Name, field.Type)
	}
}

func getString(field reflect.StructField) string {
	if envKey := field.Tag.Get("env"); envKey != "" {
		if env := os.Getenv(envKey); env != "" {
			return env
		}
	}

	if d := field.Tag.Get("default"); d != "" {
		return d
	}

	return ""
}