// Package configdiag carries value-free field diagnostics between framework
// modules without making them depend on the application's config package.
package configdiag

import "errors"

type Error struct {
	Field, Reason string
	cause         error
}

func (e *Error) Error() string       { return e.Field + ": " + e.Reason }
func (e *Error) Unwrap() error       { return e.cause }
func New(field, reason string) error { return &Error{Field: field, Reason: reason} }
func Wrap(field, reason string, cause error) error {
	return &Error{Field: field, Reason: reason, cause: cause}
}
func At(prefix string, err error) error {
	if err == nil {
		return nil
	}
	var d *Error
	if errors.As(err, &d) {
		field := prefix
		if d.Field != "" {
			if field != "" {
				field += "."
			}
			field += d.Field
		}
		return Wrap(field, d.Reason, err)
	}
	return Wrap(prefix, "validation failed", err)
}