alert.go

package sarah

import (
	"context"
	"golang.org/x/xerrors"
	"strings"
)

// Alerter can be used to report Bot's critical state to developer/administrator.
// Anything that implements this interface can be registered as Alerter via Runner.RegisterAlerter.
type Alerter interface {
	// Alert sends notification to developer/administrator so one may notify Bot's critical state.
	Alert(context.Context, BotType, error) error
}

type alertErrs []error

func (e *alertErrs) appendError(err error) {
	*e = append(*e, err)
}

func (e *alertErrs) isEmpty() bool {
	return len(*e) == 0
}

// Error returns stringified form of all stored errors.
func (e *alertErrs) Error() string {
	var errs []string
	for _, err := range *e {
		errs = append(errs, err.Error())
	}
	return strings.Join(errs, "\n")
}

type alerters []Alerter

func (a *alerters) appendAlerter(alerter Alerter) {
	*a = append(*a, alerter)
}

func (a *alerters) alertAll(ctx context.Context, botType BotType, err error) error {
	alertErrs := &alertErrs{}
	for _, alerter := range *a {
		// Considering the irregular state of Bot's lifecycle and importance of alert,
		// it is safer to be panic-proof.
		func() {
			defer func() {
				if r := recover(); r != nil {
					alertErrs.appendError(xerrors.Errorf("panic on Alerter.Alert: %w", r))
				}
			}()
			err := alerter.Alert(ctx, botType, err)
			if err != nil {
				alertErrs.appendError(err)
			}
		}()
	}

	if alertErrs.isEmpty() {
		return nil
	}
	return alertErrs
}