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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.apache.dubbo.rpc.cluster.support;

import org.apache.dubbo.common.extension.ExtensionLoader;
import org.apache.dubbo.common.logger.Logger;
import org.apache.dubbo.common.logger.LoggerFactory;
import org.apache.dubbo.common.utils.ConfigUtils;
import org.apache.dubbo.common.utils.ReflectUtils;
import org.apache.dubbo.rpc.AsyncRpcResult;
import org.apache.dubbo.rpc.Invocation;
import org.apache.dubbo.rpc.Invoker;
import org.apache.dubbo.rpc.Result;
import org.apache.dubbo.rpc.RpcException;
import org.apache.dubbo.rpc.RpcInvocation;
import org.apache.dubbo.rpc.cluster.Directory;
import org.apache.dubbo.rpc.cluster.LoadBalance;
import org.apache.dubbo.rpc.cluster.Merger;
import org.apache.dubbo.rpc.cluster.merger.MergerFactory;

import java.lang.reflect.Array;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import static org.apache.dubbo.common.constants.CommonConstants.GROUP_KEY;
import static org.apache.dubbo.rpc.Constants.ASYNC_KEY;
import static org.apache.dubbo.rpc.Constants.MERGER_KEY;

/**
 * @param 
 */
@SuppressWarnings("unchecked")
public class MergeableClusterInvoker extends AbstractClusterInvoker {

    private static final Logger log = LoggerFactory.getLogger(MergeableClusterInvoker.class);

    public MergeableClusterInvoker(Directory directory) {
        super(directory);
    }

    @Override
    protected Result doInvoke(Invocation invocation, List> invokers, LoadBalance loadbalance) throws RpcException {
        checkInvokers(invokers, invocation);
        String merger = getUrl().getMethodParameter(invocation.getMethodName(), MERGER_KEY);
        if (ConfigUtils.isEmpty(merger)) { // If a method doesn't have a merger, only invoke one Group
            for (final Invoker invoker : invokers) {
                if (invoker.isAvailable()) {
                    try {
                        return invoker.invoke(invocation);
                    } catch (RpcException e) {
                        if (e.isNoInvokerAvailableAfterFilter()) {
                            log.debug("No available provider for service" + getUrl().getServiceKey() + " on group " + invoker.getUrl().getParameter(GROUP_KEY) + ", will continue to try another group.");
                        } else {
                            throw e;
                        }
                    }
                }
            }
            return invokers.iterator().next().invoke(invocation);
        }

        Class returnType;
        try {
            returnType = getInterface().getMethod(
                    invocation.getMethodName(), invocation.getParameterTypes()).getReturnType();
        } catch (NoSuchMethodException e) {
            returnType = null;
        }

        Map results = new HashMap<>();
        for (final Invoker invoker : invokers) {
            RpcInvocation subInvocation = new RpcInvocation(invocation, invoker);
            subInvocation.setAttachment(ASYNC_KEY, "true");
            results.put(invoker.getUrl().getServiceKey(), invoker.invoke(subInvocation));
        }

        Object result = null;

        List resultList = new ArrayList(results.size());

        for (Map.Entry entry : results.entrySet()) {
            Result asyncResult = entry.getValue();
            try {
                Result r = asyncResult.get();
                if (r.hasException()) {
                    log.error("Invoke " + getGroupDescFromServiceKey(entry.getKey()) +
                                    " failed: " + r.getException().getMessage(),
                            r.getException());
                } else {
                    resultList.add(r);
                }
            } catch (Exception e) {
                throw new RpcException("Failed to invoke service " + entry.getKey() + ": " + e.getMessage(), e);
            }
        }

        if (resultList.isEmpty()) {
            return AsyncRpcResult.newDefaultAsyncResult(invocation);
        } else if (resultList.size() == 1) {
            return AsyncRpcResult.newDefaultAsyncResult(resultList.get(0).getValue(), invocation);
        }

        if (returnType == void.class) {
            return AsyncRpcResult.newDefaultAsyncResult(invocation);
        }

        if (merger.startsWith(".")) {
            merger = merger.substring(1);
            Method method;
            try {
                method = returnType.getMethod(merger, returnType);
            } catch (NoSuchMethodException e) {
                throw new RpcException("Can not merge result because missing method [ " + merger + " ] in class [ " +
                        returnType.getName() + " ]");
            }
            ReflectUtils.makeAccessible(method);
            result = resultList.remove(0).getValue();
            try {
                if (method.getReturnType() != void.class
                        && method.getReturnType().isAssignableFrom(result.getClass())) {
                    for (Result r : resultList) {
                        result = method.invoke(result, r.getValue());
                    }
                } else {
                    for (Result r : resultList) {
                        method.invoke(result, r.getValue());
                    }
                }
            } catch (Exception e) {
                throw new RpcException("Can not merge result: " + e.getMessage(), e);
            }
        } else {
            Merger resultMerger;
            if (ConfigUtils.isDefault(merger)) {
                resultMerger = MergerFactory.getMerger(returnType);
            } else {
                resultMerger = ExtensionLoader.getExtensionLoader(Merger.class).getExtension(merger);
            }
            if (resultMerger != null) {
                List