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Cattle framework cloud discovery common component pom
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/*
 * Copyright (C) 2018 the original author or 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 org.cattleframework.cloud.discovery.loadbalancer;

import java.util.List;

import org.apache.commons.collections4.CollectionUtils;
import org.cattleframework.cloud.discovery.event.LoadBalancerEvent;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.ObjectProvider;
import org.springframework.cloud.client.ServiceInstance;
import org.springframework.cloud.client.loadbalancer.EmptyResponse;
import org.springframework.cloud.client.loadbalancer.Request;
import org.springframework.cloud.client.loadbalancer.RequestData;
import org.springframework.cloud.client.loadbalancer.RequestDataContext;
import org.springframework.cloud.client.loadbalancer.Response;
import org.springframework.cloud.loadbalancer.core.NoopServiceInstanceListSupplier;
import org.springframework.cloud.loadbalancer.core.ReactorServiceInstanceLoadBalancer;
import org.springframework.cloud.loadbalancer.core.SelectedInstanceCallback;
import org.springframework.cloud.loadbalancer.core.ServiceInstanceListSupplier;

import reactor.core.publisher.Mono;

abstract class BaseCloudLoadBalancer implements ReactorServiceInstanceLoadBalancer {

    private static final Logger logger = LoggerFactory.getLogger(BaseCloudLoadBalancer.class);

    /**
     * 获得实例响应
     * 
     * @param instances 实例
     * @return 实例响应
     */
    abstract Response getInstanceResponse(List instances);

    protected final String serviceId;

    private ObjectProvider serviceInstanceListSupplierProvider;

    private final List loadBalancerEvents;

    public BaseCloudLoadBalancer(ObjectProvider serviceInstanceListSupplierProvider,
	    String serviceId, List loadBalancerEvents) {
	this.serviceId = serviceId;
	this.serviceInstanceListSupplierProvider = serviceInstanceListSupplierProvider;
	this.loadBalancerEvents = loadBalancerEvents;
    }

    @SuppressWarnings("rawtypes")
    @Override
    public Mono> choose(Request request) {
	ServiceInstanceListSupplier supplier = serviceInstanceListSupplierProvider
		.getIfAvailable(NoopServiceInstanceListSupplier::new);
	return supplier.get(request).next().map(serviceInstances -> {
	    if (serviceInstances.isEmpty()) {
		logger.warn("No servers available for service: " + serviceId);
		return new EmptyResponse();
	    }
	    filterInstances(request, serviceInstances);
	    return processInstanceResponse(supplier, serviceInstances);
	});
    }

    @SuppressWarnings("rawtypes")
    private void filterInstances(Request request, List serviceInstances) {
	RequestDataContext requestDataContext = request.getContext() != null
		&& request.getContext() instanceof RequestDataContext ? (RequestDataContext) request.getContext()
			: null;
	RequestData requestData = requestDataContext != null ? requestDataContext.getClientRequest() : null;
	if (CollectionUtils.isNotEmpty(loadBalancerEvents)) {
	    loadBalancerEvents.forEach(loadBalancerEvent -> {
		logger.debug("执行负载均衡器事件类:{}", loadBalancerEvent.getClass().getName());
		loadBalancerEvent.onFilter(requestData, serviceId, serviceInstances);
	    });
	}
    }

    private Response processInstanceResponse(ServiceInstanceListSupplier supplier,
	    List serviceInstances) {
	Response serviceInstanceResponse = getInstanceResponse(serviceInstances);
	if (supplier instanceof SelectedInstanceCallback && serviceInstanceResponse.hasServer()) {
	    ((SelectedInstanceCallback) supplier).selectedServiceInstance(serviceInstanceResponse.getServer());
	}
	return serviceInstanceResponse;
    }
}