Validate structs using reflections

reflection-validate.go

// You can edit this code!
// Click here and start typing.
package main

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

type User struct {
	Name  string `validate:"min=2,max=12"`
	Email string `validate:"required,email"`
}

func validateMinLength(
	rule string,
	field reflect.Value,
	fieldName string,
) error {
	//fmt.Println(rule, field, fieldName)
	min, _ := strconv.Atoi(
		strings.TrimPrefix(rule, "min="),
	)
	if len(field.String()) < min {
		return fmt.Errorf(
			"%s must be at least %d characters long",
			fieldName,
			min,
		)
	}
	return nil
}

func validateMaxLength(
	rule string,
	field reflect.Value,
	fieldName string,
) error {
	fmt.Println(rule, field, fieldName)
	return nil
}

func applyRule(
	rule string,
	field reflect.Value,
	fieldName string,
) error {
	switch {
	case strings.HasPrefix(rule, "min="):
		return validateMinLength(rule, field, fieldName)
	case strings.HasPrefix(rule, "max="):
		return validateMaxLength(rule, field, fieldName)

		// case strings.HasPrefix(rule, "max="):
		// 	max, _ := strconv.Atoi(
		// 		strings.TrimPrefix(rule, "max="),
		// 	)
		// 	if len(field.String()) > max {
		// 		return fmt.Errorf(
		// 			"%s must be less than %d characters long",
		// 			fieldName,
		// 			max,
		// 		)
		// 	}
		// case rule == "required":
		// 	if field.String() == "" {
		// 		return fmt.Errorf(
		// 			"%s is required",
		// 			fieldName,
		// 		)
		// 	}
		// case rule == "email":
		// 	_, err := mail.ParseAddress(field.String())
		// 	if err != nil {
		// 		return fmt.Errorf(
		// 			"%s must be a valid email address",
		// 			fieldName,
		// 		)
	}
	return nil
}

func validate(val interface{}) error {
	v := reflect.ValueOf(val)
	for i := 0; i < v.NumField(); i++ {
		field := v.Field(i)
		tag := v.Type().Field(i).Tag.Get("validate")
		fieldName := v.Type().Field(i).Name
		if tag == "" {
			continue
		}

		rules := strings.Split(tag, ",")
		for _, rule := range rules {
			if err := applyRule(rule, field, fieldName); err != nil {
				return err
			}
		}

	}
	return nil
}

func main() {
	user := User{
		Name:  "Josh",
		Email: "josh@gmail.com",
	}
	fmt.Println(validate(user))

	invalidUser := User{
		Name:  "a",
		Email: "joshm",
	}
	fmt.Println(validate(invalidUser))
}