hint.go

package errors

import (
	"fmt"
	"io"
)

type ErrHint interface{ Hint() string }

type withHint struct {
	err  error
	hint string
}

func (w *withHint) Hint() string  { return w.hint }
func (w *withHint) Error() string { return w.err.Error() }
func (w *withHint) Cause() error  { return w.err }
func (w *withHint) Unwrap() error { return w.err }

func (w *withHint) Format(s fmt.State, verb rune) {
	switch verb {
	case 'v':
		if s.Flag('+') {
			fmt.Fprintf(s, "%+v", w.Cause())
			fmt.Fprintf(s, "\nerror hint: %s", w.hint)
			return
		}
		fallthrough
	case 's':
		io.WriteString(s, w.Error())
	case 'q':
		fmt.Fprintf(s, "%q", w.Error())
	}
}

func WithHint(err error, hint string) error {
	if err == nil {
		return nil
	}
	return &withHint{err: err, hint: hint}
}

func WithHintf(err error, format string, args ...interface{}) error {
	if err == nil {
		return nil
	}
	return &withHint{err: err, hint: fmt.Sprintf(format, args...)}
}

func GetHint(err error) string {
	for e := err; e != nil; e = Unwrap(e) {
		if errDetail, ok := e.(ErrHint); ok {
			return errDetail.Hint()
		}
	}
	return ""
}