fields/fields.go

/*
 * Copyright (c) 2020 Alex aka mailoman <alex@webz.asia>
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 *
 *   @author Alex aka mailoman <alex@webz.asia>
 *   @copyright Copyright (c) 2020 Alex aka mailoman <alex@webz.asia>
 *   @since 14.01.2020
 *
 */

package fields

import (
	"log"
	"reflect"
	"strings"
)

//Convert copies field values from one struct to another based on tags setup
func Сonvert(from interface{}, kind string, to interface{}) {
	if nil == from {
		log.Print("nil value is not supported")

		return
	}

	v := reflect.ValueOf(from)
	vt := reflect.ValueOf(to)
	t := v.Type()

	if t.Kind() != reflect.Struct {
		log.Printf("type %s is not supported", t.Kind())

		return
	}

	if vt.Kind() == reflect.Ptr {
		vt = reflect.ValueOf(to).Elem()
	}

	for i := 0; i < t.NumField(); i++ {
		f := t.Field(i)
		// skip unexported fields. from godoc:
		// PkgPath is the package path that qualifies a lower case (unexported)
		// field name. It is empty for upper case (exported) field names.
		if f.PkgPath != "" && f.Name == "" {
			continue
		}
		fv := v.Field(i)
		found, omit, omitempty := readTag(f, kind)
		// skip if tag "omit" set.
		if omit {
			continue
		}
		// skip empty values when "omitempty" set.
		if omitempty && fv.String() == "" {
			continue
		}

		if found {
			ft := vt.FieldByName(f.Name)
			if !ft.IsValid() && fv.Kind() == reflect.Struct {
				Сonvert(fv.Interface(), kind, to)
			} else {
				ft.Set(fv)
			}
		}
	}
}

func readTag(f reflect.StructField, kind string) (bool, bool, bool) {
	val, ok := f.Tag.Lookup(ConvertTagName())
	if !ok {
		return false, false, false
	}
	opts := strings.Split(val, ",")

	return indexOf(opts, kind) > -1, indexOf(opts, OmitTagName()) > -1, indexOf(opts, OmitEmptyTagName()) > -1
}

func indexOf(a []string, x string) int {
	for i, n := range a {
		if x == n {
			return i
		}
	}

	return -1
}