valid/messages.go

package valid

import "fmt"

// MessageProvider maps a validation failure to a human-readable message.
//
//   - field: the struct field name (e.g. "Email")
//   - tag:   the failing validation rule (e.g. "required", "email", "min")
//   - param: the rule parameter if any (e.g. "18" for min=18), or "" if none
type MessageProvider interface {
	Message(field, tag, param string) string
}

// DefaultMessages is the built-in English message provider.
// Used automatically when no WithMessageProvider option is given.
var DefaultMessages MessageProvider = defaultMessages{}

// SpanishMessages is an opt-in Spanish message provider.
var SpanishMessages MessageProvider = spanishMessages{}

// ---------------------------------------------------------------
// English (default)
// ---------------------------------------------------------------

type defaultMessages struct{}

func (defaultMessages) Message(field, tag, param string) string {
	switch tag {
	case "required":
		return fmt.Sprintf("field '%s' is required", field)
	case "email":
		return fmt.Sprintf("field '%s' must be a valid email address", field)
	case "min":
		return fmt.Sprintf("field '%s' is too short (minimum %s)", field, param)
	case "max":
		return fmt.Sprintf("field '%s' is too long (maximum %s)", field, param)
	default:
		return fmt.Sprintf("field '%s' failed validation rule '%s'", field, tag)
	}
}

// ---------------------------------------------------------------
// Spanish (opt-in)
// ---------------------------------------------------------------

type spanishMessages struct{}

func (spanishMessages) Message(field, tag, param string) string {
	switch tag {
	case "required":
		return fmt.Sprintf("El campo '%s' es obligatorio", field)
	case "email":
		return fmt.Sprintf("El campo '%s' debe ser un correo electrónico válido", field)
	case "min":
		return fmt.Sprintf("El campo '%s' es demasiado corto (mínimo %s)", field, param)
	case "max":
		return fmt.Sprintf("El campo '%s' es demasiado largo (máximo %s)", field, param)
	default:
		return fmt.Sprintf("Error en el campo '%s': regla '%s' no cumplida", field, tag)
	}
}