const (
	// MaxPublishRequestCount is the maximum number of messages that can be
	// batched in a single publish request.
	MaxPublishRequestCount = 1000

	// MaxPublishRequestBytes is the maximum allowed serialized size of a single
	// publish request (containing a batch of messages) in bytes. Must be lower
	// than the gRPC limit of 4 MiB.
	MaxPublishRequestBytes int = 3.5 * 1024 * 1024

	// MinTimeout is the minimum timeout value that can be set for publisher and
	// subscriber settings.
	MinTimeout = 2 * time.Minute
)

var (
	// ErrOverflow indicates that the publish buffers have overflowed. See
	// comments for PublishSettings.BufferedByteLimit.
	ErrOverflow = errors.New("pubsublite: client-side publish buffers have overflowed")

	// ErrOversizedMessage indicates that the user published a message over the
	// allowed serialized byte size limit. It is wrapped in another error.
	ErrOversizedMessage = fmt.Errorf("maximum allowed message size is MaxPublishRequestBytes (%d)", MaxPublishRequestBytes)

	// ErrServiceUninitialized indicates that a service (e.g. publisher or
	// subscriber) cannot perform an operation because it is uninitialized.
	ErrServiceUninitialized = errors.New("pubsublite: service must be started")

	// ErrServiceStarting indicates that a service (e.g. publisher or subscriber)
	// cannot perform an operation because it is starting up.
	ErrServiceStarting = errors.New("pubsublite: service is starting up")

	// ErrServiceStopped indicates that a service (e.g. publisher or subscriber)
	// cannot perform an operation because it has stopped or is in the process of
	// stopping.
	ErrServiceStopped = errors.New("pubsublite: service has stopped or is stopping")

	// ErrBackendUnavailable indicates that the backend service has been
	// unavailable for a period of time. The timeout can be configured using
	// PublishSettings.Timeout or ReceiveSettings.Timeout.
	ErrBackendUnavailable = errors.New("pubsublite: backend service is unavailable")
)

var DefaultPublishSettings = PublishSettings{
	DelayThreshold: 10 * time.Millisecond,
	CountThreshold: 100,
	ByteThreshold:  1e6,
	Timeout:        7 * 24 * time.Hour,

	BufferedByteLimit: 1 << 30,
	EnableIdempotence: true,
	ConfigPollPeriod:  10 * time.Minute,
}

var DefaultReceiveSettings = ReceiveSettings{
	MaxOutstandingMessages: 1000,
	MaxOutstandingBytes:    1e9,
	Timeout:                7 * 24 * time.Hour,
}

type AckConsumer interface {
	Ack()
}

type FrameworkType string

const FrameworkCloudPubSubShim FrameworkType = "CLOUD_PUBSUB_SHIM"

type LocationPath struct {
	// A Google Cloud project. The project ID (e.g. "my-project") or the project
	// number (e.g. "987654321") can be provided.
	Project string

	// A Google Cloud zone (e.g. "us-central1-a") or region (e.g. "us-central1").
	Location string
}

type MessageMetadata struct {
	// The topic partition the message was published to.
	Partition int

	// The offset the message was assigned.
	Offset int64
}

type MessageReceiverFunc func(*ReceivedMessage)

type PartitionSet map[int]struct{}

type PublishResultFunc func(*MessageMetadata, error)

type PublishSettings struct {
	// Publish a non-empty batch after this delay has passed. Must be > 0.
	DelayThreshold time.Duration

	// Publish a batch when it has this many messages. Must be > 0. The maximum is
	// MaxPublishRequestCount.
	CountThreshold int

	// Publish a batch when its size in bytes reaches this value. Must be > 0. The
	// maximum is MaxPublishRequestBytes.
	ByteThreshold int

	// The maximum time that the client will attempt to establish a publish stream
	// connection to the server. Must be >= 2 minutes.
	//
	// The timeout is exceeded, the publisher will terminate with the last error
	// that occurred while trying to reconnect. Note that if the timeout duration
	// is long, ErrOverflow may occur first.
	Timeout time.Duration

	// The maximum number of bytes that the publisher will keep in memory before
	// returning ErrOverflow. Must be > 0.
	//
	// Note that Pub/Sub Lite topics are provisioned a publishing throughput
	// capacity, per partition, shared by all publisher clients. Setting a large
	// buffer size can mitigate transient publish spikes. However, consistently
	// attempting to publish messages at a much higher rate than the publishing
	// throughput capacity can cause the buffers to overflow. For more
	// information, see https://cloud.google.com/pubsub/lite/docs/topics.
	BufferedByteLimit int

	// The polling interval to watch for topic partition count updates. Set to 0
	// to disable polling if the number of partitions will never update.
	ConfigPollPeriod time.Duration

	// Whether idempotence is enabled, where the server will ensure that unique
	// messages within a single publisher session are stored only once.
	EnableIdempotence bool

	// The user-facing API type.
	Framework FrameworkType
}

type Publisher interface {
	Publish(*pb.PubSubMessage, PublishResultFunc)

	Start()
	WaitStarted() error
	Stop()
	WaitStopped() error
	Error() error
}

type ReassignmentHandlerFunc func(before, after PartitionSet) error

type ReceiveSettings struct {
	// MaxOutstandingMessages is the maximum number of unacknowledged messages.
	// Must be > 0.
	MaxOutstandingMessages int

	// MaxOutstandingBytes is the maximum size (in quota bytes) of unacknowledged
	// messages. Must be > 0.
	MaxOutstandingBytes int

	// The maximum time that the client will attempt to establish a subscribe
	// stream connection to the server. Must be >= 2 minutes.
	//
	// The timeout is exceeded, the subscriber will terminate with the last error
	// that occurred while trying to reconnect.
	Timeout time.Duration

	// The topic partition numbers (zero-indexed) to receive messages from.
	// Values must be less than the number of partitions for the topic. If not
	// specified, the client will use the partition assignment service to
	// determine which partitions it should connect to.
	Partitions []int

	// The user-facing API type.
	Framework FrameworkType
}

type ReceivedMessage struct {
	Msg       *pb.SequencedMessage
	Ack       AckConsumer
	Partition int
}

type ReservationPath struct {
	// A Google Cloud project. The project ID (e.g. "my-project") or the project
	// number (e.g. "987654321") can be provided.
	Project string

	// A Google Cloud region. An example region is "us-central1".
	Region string

	// The ID of the Pub/Sub Lite reservation, for example "my-reservation-name".
	ReservationID string
}

type Subscriber interface {
	Start()
	WaitStarted() error
	Stop()
	WaitStopped() error
	Terminate()
	PartitionActive(int) bool
}

type SubscriptionPath struct {
	// A Google Cloud project. The project ID (e.g. "my-project") or the project
	// number (e.g. "987654321") can be provided.
	Project string

	// A Google Cloud zone (e.g. "us-central1-a") or region (e.g. "us-central1").
	Location string

	// The ID of the Pub/Sub Lite subscription, for example
	// "my-subscription-name".
	SubscriptionID string
}

type TopicPath struct {
	// A Google Cloud project. The project ID (e.g. "my-project") or the project
	// number (e.g. "987654321") can be provided.
	Project string

	// A Google Cloud zone (e.g. "us-central1-a") or region (e.g. "us-central1").
	Location string

	// The ID of the Pub/Sub Lite topic, for example "my-topic-name".
	TopicID string
}