goenv.go

// Package goenv provides a simple way to populate the fields of a struct with
// the values of the environment variables.
package goenv

import (
	"errors"
	"os"
	"reflect"

	"github.com/ggicci/owl"
)

var (
	ErrMissingName = errors.New("missing name of the environment variable")
	ErrInvalidType = errors.New("only string field can be tagged with env")
)

func nameDirective(rtm *owl.DirectiveRuntime) error {
	if len(rtm.Directive.Argv) == 0 {
		return ErrMissingName
	}
	if value, ok := os.LookupEnv(rtm.Directive.Argv[0]); ok {
		if rtm.Value.Elem().Type().Kind() != reflect.String {
			return ErrInvalidType
		}
		rtm.Value.Elem().SetString(value)
	}
	return nil
}

func init() {
	owl.UseTag("env")
	owl.RegisterDirectiveExecutor("name", owl.DirectiveExecutorFunc(nameDirective))
}

// Load populates the fields of the value with the values of the environment variables.
func Load(value interface{}) error {
	resolver, err := owl.New(value)
	if err != nil {
		return err
	}
	return resolver.ResolveTo(value)
}