// Package validation uses github.com/go-playground/validator/v10 for API request validation.
package validation

import (
	"fmt"

	"github.com/go-playground/validator/v10"
)

var defaultValidator = validator.New()

// Struct validates s and returns the first validation error as a readable message, or nil.
func Struct(s any) error {
	err := defaultValidator.Struct(s)
	if err == nil {
		return nil
	}
	if errs, ok := err.(validator.ValidationErrors); ok && len(errs) > 0 {
		fe := errs[0]
		return fmt.Errorf("%s: %s", fe.Field(), fe.Tag())
	}
	return err
}

// Var validates a single value with the given tag (e.g. "required") and returns an error or nil.
func Var(field any, tag string) error {
	err := defaultValidator.Var(field, tag)
	if err == nil {
		return nil
	}
	if errs, ok := err.(validator.ValidationErrors); ok && len(errs) > 0 {
		fe := errs[0]
		return fmt.Errorf("%s", fe.Tag())
	}
	return err
}