refactor and organize code

internal/gperr/utils.go

@@ -0,0 +1,93 @@
+package gperr
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+)
+
+func newError(message string) error {
+	return errStr(message)
+}
+
+func New(message string) Error {
+	if message == "" {
+		return nil
+	}
+	return &baseError{newError(message)}
+}
+
+func Errorf(format string, args ...any) Error {
+	return &baseError{fmt.Errorf(format, args...)}
+}
+
+// Wrap wraps message in front of the error message.
+func Wrap(err error, message ...string) Error {
+	if err == nil {
+		return nil
+	}
+	if len(message) == 0 || message[0] == "" {
+		return wrap(err)
+	}
+	//nolint:errorlint
+	switch err := err.(type) {
+	case *baseError:
+		err.Err = fmt.Errorf("%s: %w", message[0], err.Err)
+		return err
+	case *nestedError:
+		err.Err = fmt.Errorf("%s: %w", message[0], err.Err)
+		return err
+	}
+	return &baseError{fmt.Errorf("%s: %w", message[0], err)}
+}
+
+func wrap(err error) Error {
+	if err == nil {
+		return nil
+	}
+	//nolint:errorlint
+	switch err := err.(type) {
+	case Error:
+		return err
+	}
+	return &baseError{err}
+}
+
+func IsJSONMarshallable(err error) bool {
+	switch err := err.(type) {
+	case *nestedError, *withSubject:
+		return true
+	case *baseError:
+		return IsJSONMarshallable(err.Err)
+	default:
+		var v json.Marshaler
+		return errors.As(err, &v)
+	}
+}
+
+func Join(errors ...error) Error {
+	n := 0
+	for _, err := range errors {
+		if err != nil {
+			n++
+		}
+	}
+	if n == 0 {
+		return nil
+	}
+	errs := make([]error, n)
+	i := 0
+	for _, err := range errors {
+		if err != nil {
+			errs[i] = err
+			i++
+		}
+	}
+	return &nestedError{Extras: errs}
+}
+
+func Collect[T any, Err error, Arg any, Func func(Arg) (T, Err)](eb *Builder, fn Func, arg Arg) T {
+	result, err := fn(arg)
+	eb.Add(err)
+	return result
+}