app

type App interface {
	// Init initializes the application in a blocking fashion. When Init returns, it
	// is expected that the application is ready to start receiving requests (provided
	// there are gRPC handlers installed).
	//
	// todo: I'm not very happy with passing the New Relic app here. It's a temporary
	//       solution until we have something better in place.
	Init(config Config, metricsProvider *newrelic.Application) error

	// RegisterWithGRPC provides a mechanism for the application to register gRPC services
	// with the gRPC server.
	RegisterWithGRPC(server *grpc.Server)

	// ShutdownChan returns a channel that is closed when the application is shutdown.
	//
	// If the channel is closed, the gRPC server will initiate a shutdown if it has
	// not already done so.
	ShutdownChan() <-chan struct{}

	// Stop stops the service, allowing for it to clean up any resources. When Stop()
	// returns, the process exits.
	//
	// Stop should be idempotent.
	Stop()
}

type BaseConfig struct {
	LogLevel string `mapstructure:"log_level"`

	AppName string `mapstructure:"app_name"`

	ListenAddress         string `mapstructure:"listen_address"`
	InsecureListenAddress string `mapstructure:"insecure_listen_address"`
	DebugListenAddress    string `mapstructure:"debug_listen_address"`

	// TLSCertificate is an optional URL that specified a TLS certificate to be
	// used for the gRPC server.
	//
	// Currently only two supported URL schemes are supported: file, s3.
	// If no scheme is specified, file is used.
	TLSCertificate string `mapstructure:"tls_certificate"`
	// TLSKey is an optional URL that specifies a TLS Private Key to be used for the
	// gRPC server.
	//
	// Currently only two supported URL schemes are supported: file, s3.
	// If no scheme is specified, file is used.
	TLSKey string `mapstructure:"tls_private_key"`

	ShutdownGracePeriod time.Duration `mapstructure:"shutdown_grace_period"`

	EnablePprof  bool `mapstructure:"enable_pprof"`
	EnableExpvar bool `mapstructure:"enable_expvar"`

	// Ballast for improving Go GC performance. Note that capacity will be
	// limited to 50% of the total memory.
	// https://blog.twitch.tv/en/2019/04/10/go-memory-ballast-how-i-learnt-to-stop-worrying-and-love-the-heap/
	EnableBallast   bool    `mapstructure:"enable_ballast"`
	BallastCapacity float32 `mapstructure:"ballast_capacity"`

	// Periodically terminate the application when there's a memory leak
	EnableMemoryLeakCron   bool   `mapstructure:"enable_memory_leak_cron"`
	MemoryLeakCronSchedule string `mapstructure:"memory_leak_cron_schedule"`

	// Metrics configuration across many providers
	NewRelicLicenseKey string `mapstructure:"new_relic_license_key"`

	// Arbitrary configuration that the service can define / implement.
	//
	// Users should use mapstructure.Decode for ServiceConfig.
	AppConfig Config `mapstructure:"app"`
}

type Config map[string]interface{}

type FileLoader interface {
	Load(url *url.URL) ([]byte, error)
}

type FileLoaderCtor func() (FileLoader, error)

type Option func(o *opts)