valid/valid.go

package valid

import (
	"errors"
	"reflect"
	"strings"

	"code.nochebuena.dev/go/xerrors"
	playground "github.com/go-playground/validator/v10"
)

// Validator validates structs using struct tags.
type Validator interface {
	// Struct validates v and returns a *xerrors.Err if validation fails.
	// Returns nil if v is valid.
	// Returns ErrInvalidInput for field constraint failures (first error only).
	// Returns ErrInternal if v is not a struct.
	Struct(v any) error
}

// Option configures a Validator.
type Option func(*config)

// config holds constructor configuration.
type config struct {
	mp MessageProvider
}

// WithMessageProvider sets a custom MessageProvider.
// Default: DefaultMessages (English).
func WithMessageProvider(mp MessageProvider) Option {
	return func(c *config) {
		c.mp = mp
	}
}

// New returns a Validator. Without options, DefaultMessages (English) is used.
// Field names in error context use the json struct tag when available,
// falling back to the Go field name.
func New(opts ...Option) Validator {
	cfg := &config{mp: DefaultMessages}
	for _, o := range opts {
		o(cfg)
	}
	v := playground.New()
	v.RegisterTagNameFunc(func(fld reflect.StructField) string {
		name := strings.SplitN(fld.Tag.Get("json"), ",", 2)[0]
		if name == "" || name == "-" {
			return fld.Name
		}
		return name
	})
	return &validator{
		v:  v,
		mp: cfg.mp,
	}
}

// validator is the concrete implementation of Validator.
type validator struct {
	v  *playground.Validate
	mp MessageProvider
}

// Struct implements Validator.
//
// Only the first validation error is surfaced. Apps needing all failures can
// cast errors.Unwrap(err) to validator.ValidationErrors themselves.
func (val *validator) Struct(v any) error {
	err := val.v.Struct(v)
	if err == nil {
		return nil
	}

	var invalidErr *playground.InvalidValidationError
	if errors.As(err, &invalidErr) {
		return xerrors.Wrap(xerrors.ErrInternal, "internal validation error", err)
	}

	var validationErrs playground.ValidationErrors
	if errors.As(err, &validationErrs) {
		first := validationErrs[0]
		msg := val.mp.Message(first.Field(), first.Tag(), first.Param())
		return xerrors.New(xerrors.ErrInvalidInput, msg).
			WithContext("field", first.Field()).
			WithContext("tag", first.Tag()).
			WithError(err)
	}

	return xerrors.Wrap(xerrors.ErrInternal, "internal validation error", err)
}