/*
 *
 * Copyright 2014 gRPC authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */

// Package naming defines the naming API and related data structures for gRPC.
// The interface is EXPERIMENTAL and may be suject to change.
package naming

// Operation defines the corresponding operations for a name resolution change.
type Operation uint8

const (
	// Add indicates a new address is added.
	Add Operation = iota
	// Delete indicates an exisiting address is deleted.
	Delete
)

// Update defines a name resolution update. Notice that it is not valid having both
// empty string Addr and nil Metadata in an Update.
type Update struct {
	// Op indicates the operation of the update.
	Op Operation
	// Addr is the updated address. It is empty string if there is no address update.
	Addr string
	// Metadata is the updated metadata. It is nil if there is no metadata update.
	// Metadata is not required for a custom naming implementation.
	Metadata interface{}
}

// Resolver creates a Watcher for a target to track its resolution changes.
type Resolver interface {
	// Resolve creates a Watcher for target.
	Resolve(target string) (Watcher, error)
}

// Watcher watches for the updates on the specified target.
type Watcher interface {
	// Next blocks until an update or error happens. It may return one or more
	// updates. The first call should get the full set of the results. It should
	// return an error if and only if Watcher cannot recover.
	Next() ([]*Update, error)
	// Close closes the Watcher.
	Close()
}