package resolver

import (
	"gitee.com/h79/goutils/common/attributes"
)

var (
	// m is a map from scheme to resolver builder.
	m = make(map[string]Builder)
)

func Register(b Builder) {
	m[b.Scheme()] = b
}

// Get returns the resolver builder registered with the given scheme.
//
// If no builder is register with the scheme, nil will be returned.
func Get(scheme string) Builder {
	if b, ok := m[scheme]; ok {
		return b
	}
	return nil
}

type Target struct {
	Scheme    string
	Authority string
	Endpoint  string
}

// Builder creates a resolver that will be used to watch name resolution updates.
type Builder interface {
	// Build creates a new resolver for the given target.
	//
	// gRPC dial calls Build synchronously, and fails if the returned error is
	// not nil.
	Build(target Target, cc Connector) (Resolver, error)

	// Scheme returns the scheme supported by this resolver.
	// Scheme is defined at https://github.com/grpc/grpc/blob/master/doc/naming.md.
	Scheme() string
}

// Resolver watches for the updates on the specified target.
// Updates include address updates and service config updates.
type Resolver interface {
	// ResolveNow will be called by gRPC to try to resolve the target name
	// again. It's just a hint, resolver can ignore this if it's not necessary.
	//
	// It could be called multiple times concurrently.
	ResolveNow()

	// Close closes the resolver.
	Close()
}

type Connector interface {
	// UpdateState updates the state of the ClientConn appropriately.
	UpdateState(State)

	// ReportError notifies the ClientConn that the Resolver encountered an
	// error.  The ClientConn will notify the load balancer and begin calling
	// ResolveNow on the Resolver with exponential backoff.
	ReportError(error)
}

// Notice: This type is EXPERIMENTAL and may be changed or removed in a
// later release.
type Address struct {
	// Addr is the server address on which a connection will be established.
	Addr string

	// ServerName is the name of this address.
	// If non-empty, the ServerName is used as the transport certification authority for
	// the address, instead of the hostname from the Dial target string. In most cases,
	// this should not be set.
	//
	// If Method is GRPCLB, ServerName should be the name of the remote load
	// balancer, not the name of the backend.
	//
	// WARNING: ServerName must only be populated with trusted values. It
	// is insecure to populate it with data from untrusted inputs since untrusted
	// values could be used to bypass the authority checks performed by TLS.
	ServerName string

	// Attributes contains arbitrary data about this address intended for
	// consumption by the load balancing policy.
	Attributes *attributes.Attributes
}

// State contains the current Resolver state relevant to the ClientConn.
type State struct {
	// Addresses is the latest set of resolved addresses for the target.
	Addresses []Address

	// Attributes contains arbitrary data about the resolver intended for
	// consumption by the load balancing policy.
	Attributes *attributes.Attributes
}