var (
	// DefaultKeepaliveInterval contains default duration between grpc keepalive
	DefaultKeepaliveInterval    = 10 * time.Second
	MinKeepaliveInterval        = 10 * time.Second
	DefaultGRPCMsgSize          = 64 * 1024 * 1024 // 64MB
	DefaultGrpcConnectionPolicy = keepalive.ClientParameters{
		Time:                DefaultKeepaliveInterval,
		Timeout:             MinKeepaliveInterval,
		PermitWithoutStream: true,
	}
)

type Config interface {
	// Endpoint is a required starting endpoint for connect
	Endpoint() string

	// Database is a required database name.
	Database() string

	// Secure is an flag for secure connection
	Secure() bool

	// Credentials is an ydb client credentials.
	// In most cases Credentials are required.
	Credentials() credentials.Credentials

	// Trace contains driver tracing options.
	Trace() trace.Driver

	// OperationTimeout is the maximum amount of time a YDB server will process
	// an operation. After timeout exceeds YDB will try to cancel operation and
	// regardless of the cancellation appropriate error will be returned to
	// the client.
	// If OperationTimeout is zero then no timeout is used.
	OperationTimeout() time.Duration

	// OperationCancelAfter is the maximum amount of time a YDB server will process an
	// operation. After timeout exceeds YDB will try to cancel operation and if
	// it succeeds appropriate error will be returned to the client; otherwise
	// processing will be continued.
	// If OperationCancelAfter is zero then no timeout is used.
	OperationCancelAfter() time.Duration

	// Balancer is an optional configuration related to selected balancer.
	// That is, some balancing methods allow to be configured.
	Balancer() balancer.Balancer

	// RequestsType set an additional type hint to all requests.
	// It is needed only for debug purposes and advanced cases.
	RequestsType() string

	// DialTimeout is the maximum amount of time a dial will wait for a connect to
	// complete.
	// If DialTimeout is zero then no timeout is used.
	DialTimeout() time.Duration

	// GrpcDialOptions is an custom client grpc dial options which will appends to
	// default grpc dial options
	GrpcDialOptions() []grpc.DialOption

	// ConnectionTTL is a time to live of a connection
	// If ConnectionTTL is zero then TTL is not used.
	ConnectionTTL() time.Duration

	// Meta is an option which contains meta information about database connection
	Meta() meta.Meta

	// UseDNSResolver is a flag about using dns-resolving or not
	UseDNSResolver() bool

	// ExcludeGRPCCodesForPessimization defines grpc codes for exclude its from pessimization trigger
	ExcludeGRPCCodesForPessimization() []grpcCodes.Code
}

type Option func(c *config)