naming

type BuildOpt interface {
	Apply(*BuildOptions)
}

type BuildOptions struct {
	Filter     func(map[string][]*Instance) map[string][]*Instance
	Subset     func([]*Instance, int) []*Instance
	SubsetSize int
	ClientZone string
	Scheduler  func(*InstancesInfo) []*Instance
}

type Builder interface {
	Build(id string, options ...BuildOpt) Resolver
	Scheme() string
}

type Instance struct {
	// Region is region.
	Region string `json:"region"`
	// Zone is IDC.
	Zone string `json:"zone"`
	// Env prod/pre、uat/fat1
	Env string `json:"env"`
	// AppID is mapping servicetree appid.
	AppID string `json:"appid"`
	// Hostname is hostname from docker.
	Hostname string `json:"hostname"`
	// Addrs is the address of app instance
	// format: scheme://host
	Addrs []string `json:"addrs"`
	// Version is publishing version.
	Version string `json:"version"`
	// LastTs is instance latest updated timestamp
	LastTs int64 `json:"latest_timestamp"`
	// Metadata is the information associated with Addr, which may be used
	// to make load balancing decision.
	Metadata map[string]string `json:"metadata"`
	// Status instance status, eg: 1UP 2Waiting
	Status int64 `json:"status"`
}

type InstancesInfo struct {
	Instances map[string][]*Instance `json:"instances"`
	LastTs    int64                  `json:"latest_timestamp"`
	Scheduler *Scheduler             `json:"scheduler"`
}

type Registry interface {
	Register(ctx context.Context, ins *Instance) (cancel context.CancelFunc, err error)
	Close() error
}

type Resolver interface {
	Fetch(context.Context) (*InstancesInfo, bool)
	Watch() <-chan struct{}
	Close() error
}

type Scheduler struct {
	Clients map[string]*ZoneStrategy `json:"clients"`
}

type Strategy struct {
	Weight int64 `json:"weight"`
}

type ZoneStrategy struct {
	Zones map[string]*Strategy `json:"zones"`
}