struct.go

package flagstruct

import "reflect"

// fieldData contains StructField and Value of a property,
// that extracted from input struct
type fieldData struct {
	field reflect.StructField
	value reflect.Value
	tag   *tagData
}

// structVal returns reflect.Value of struct
func structVal(i interface{}) reflect.Value {
	v := reflect.ValueOf(i)

	// if pointer get the underlying element≤
	if v.Kind() == reflect.Ptr {
		v = v.Elem()
	}

	if v.Kind() != reflect.Struct {
		panic("not struct")
	}

	return v
}

// structFields returns list of field and data which have tag flag
func structFields(i interface{}) []fieldData {
	sv := structVal(i)
	return getFields(sv)
}

func getFields(v reflect.Value) []fieldData {
	var f []fieldData

	t := v.Type()
	for i := 0; i < t.NumField(); i = i + 1 {
		field := t.Field(i)

		if field.Anonymous {
			av := v.FieldByName(field.Name)
			if av.Kind() == reflect.Ptr {
				av = av.Elem()
			}

			if av.IsValid() == false {
				continue
			}

			if fields := getFields(av); len(fields) > 0 {
				f = append(f, fields...)
			}

			continue
		}

		if td := parseTag(field); td != nil {
			fd := fieldData{
				field: field,
				value: v.FieldByName(field.Name),
				tag:   td,
			}

			f = append(f, fd)
		}
	}

	return f
}

// isStructPointer returns true if the given interface is a pointer to a struct.
func isStructPointer(s interface{}) bool {
	v := reflect.ValueOf(s)
	if v.Kind() == reflect.Ptr {
		v = v.Elem()
	} else {
		return false
	}

	return v.Kind() == reflect.Struct
}