oklahomer/go-sarah

package sarah

import (
    "context"
    "errors"
    "fmt"
)

// ErrWatcherNotRunning is returned when ConfigWatcher.Unwatch is called but the context is already canceled.
var ErrWatcherNotRunning = errors.New("context is already canceled")

// ErrAlreadySubscribing is returned when duplicated calls to ConfigWatcher.Watch occur.
var ErrAlreadySubscribing = errors.New("already subscribing")

// ConfigNotFoundError is returned when a corresponding configuration is not found.
// This is typically returned when the caller tries to see if there is any configuration available via ConfigWatcher.Read.
type ConfigNotFoundError struct {
    BotType BotType
    ID      string
}

// Error returns stringified representation of the error.
func (err *ConfigNotFoundError) Error() string {
    return fmt.Sprintf("no configuration found for %s:%s", err.BotType, err.ID)
}

var _ error = (*ConfigNotFoundError)(nil)

// ConfigWatcher defines an interface that all "watcher" implementations must satisfy.
// A watcher subscribes to any change on the configuration setting of Command or ScheduledTask.
// When a change is detected, ConfigWatcher calls the callback function to apply the change to the configuration values Command or ScheduledTask is referring to.
// One example could be watchers.fileWatcher that subscribes to configuration file changes;
// while another reference implementation -- https://github.com/oklahomer/go-sarah-githubconfig -- subscribes to changes on a given GitHub repository.
type ConfigWatcher interface {
    // Read reads the latest configuration value and apply that value to configPtr.
    Read(botCtx context.Context, botType BotType, id string, configPtr interface{}) error
    // Watch subscribes to given id's configuration.
    // When a change to the corresponding configuration value occurs, callback is called.
    // A call to callback function triggers go-sarah's core to call Read() to reflect the latest configuration value.
    Watch(botCtx context.Context, botType BotType, id string, callback func()) error
    // Unwatch is called when Bot is stopped and subscription is no longer required.
    Unwatch(botType BotType) error
}

type nullConfigWatcher struct{}

var _ ConfigWatcher = (*nullConfigWatcher)(nil)

func (*nullConfigWatcher) Read(_ context.Context, _ BotType, _ string, _ interface{}) error {
    return nil
}

func (*nullConfigWatcher) Watch(_ context.Context, _ BotType, _ string, _ func()) error {
    return nil
}

func (*nullConfigWatcher) Unwatch(_ BotType) error {
    return nil
}