package internal

import (
	"fmt"
	"reflect"
	"strings"
)

func NilChecker(data any) error {
	val := reflect.ValueOf(data)

	if val.Kind() == reflect.Ptr {
		val = val.Elem()
	}

	valType := val.Type()

	if val.Kind() != reflect.Struct {
		return fmt.Errorf("data is not a struct")
	}

	nilFields := []string{}
	for i := range val.NumField() {
		field := val.Field(i)
		fieldType := valType.Field(i)
		tagValue := fieldType.Tag.Get("nil_checker")

		if tagValue == "required" {
			if field.Kind() == reflect.Ptr {
				if field.IsNil() {
					nilFields = append(nilFields, fieldType.Name)
				}
			}
		}
	}
	if len(nilFields) > 0 {
		return fmt.Errorf("%s is empty", strings.Join(nilFields, ","))
	}
	return nil
}