type Endpoint struct {
	// Addr is the server address on which a connection will be established.
	// Since etcd 3.1
	Addr string

	// Metadata is the information associated with Addr, which may be used
	// to make load balancing decision.
	// Since etcd 3.1
	//
	// Deprecated: The field is deprecated and will be removed in 3.7.
	Metadata any
}

type Key2EndpointMap map[string]Endpoint

type Manager interface {
	// Update allows to atomically add/remove a few endpoints from etcd.
	Update(ctx context.Context, updates []*UpdateWithOpts) error

	// AddEndpoint registers a single endpoint in etcd.
	// For more advanced use-cases use the Update method.
	AddEndpoint(ctx context.Context, key string, endpoint Endpoint, opts ...clientv3.OpOption) error
	// DeleteEndpoint deletes a single endpoint stored in etcd.
	// For more advanced use-cases use the Update method.
	DeleteEndpoint(ctx context.Context, key string, opts ...clientv3.OpOption) error

	// List returns all the endpoints for the current target as a map.
	List(ctx context.Context) (Key2EndpointMap, error)
	// NewWatchChannel creates a channel that populates or endpoint updates.
	// Cancel the 'ctx' to close the watcher.
	NewWatchChannel(ctx context.Context) (WatchChannel, error)
}

type Operation uint8

const (
	// Add indicates an Endpoint is added.
	Add Operation = iota
	// Delete indicates an existing address is deleted.
	Delete
)

type Update struct {
	// Op - action Add or Delete.
	Op       Operation
	Key      string
	Endpoint Endpoint
}

type UpdateWithOpts struct {
	Update
	Opts []clientv3.OpOption
}

type WatchChannel <-chan []*Update