/*
 * Copyright 1999-2018 Alibaba Group Holding Ltd.
 *
 * 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 com.alibaba.nacos.naming.selector;

import com.alibaba.nacos.naming.core.Instance;
import com.fasterxml.jackson.annotation.JsonTypeInfo;
import com.fasterxml.jackson.annotation.JsonTypeInfo.Id;

import java.util.List;

/**
 * Selector defines a rule for load-balance for service discovery.
 *
 * <p>Every service in Nacos can apply an existing selector and uses it to give the consumer a subset of selected
 * providers.
 *
 * <p>This selector itself does not implement any specific behavior of load-balance, every real life selector should
 * extend this class and implement the select method.
 *
 * <p>Every extended selector should also register its type to class SelectorType so Nacos recognizes it and can
 * correctly create this type of selector.
 *
 * <p>Sub class should register their type to JacksonUtil.
 *
 * @author nkorange
 * @see com.alibaba.nacos.api.selector.SelectorType
 * @see com.alibaba.nacos.common.utils.JacksonUtils
 * @since 0.7.0
 */
@JsonTypeInfo(use = Id.NAME, property = "type", defaultImpl = NoneSelector.class)
public interface Selector {
    
    /**
     * Get the type of this selector.
     *
     * @return type of selector
     */
    String getType();
    
    /**
     * Select qualified instances from providers.
     *
     * @param consumer  consumer address
     * @param providers candidate provider addresses
     * @return selected provider addresses
     */
    List<Instance> select(String consumer, List<Instance> providers);
}
