/**
 * 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.camel.processor.loadbalancer;

import java.util.List;

import org.apache.camel.AsyncCallback;
import org.apache.camel.AsyncProcessor;
import org.apache.camel.Exchange;
import org.apache.camel.Processor;

/**
 * A base class for {@link LoadBalancer} implementations which choose a single
 * destination for each exchange (rather like JMS Queues)
 * 
 * @version $Revision: 1951 $
 */
public abstract class QueueLoadBalancer extends LoadBalancerSupport {

    public void process(Exchange exchange) throws Exception {
        List<Processor> list = getProcessors();
        if (list.isEmpty()) {
            throw new IllegalStateException("No processors available to process " + exchange);
        }
        Processor processor = chooseProcessor(list, exchange);
        if (processor == null) {
            throw new IllegalStateException("No processors could be chosen to process " + exchange);
        } else {
            processor.process(exchange);
        }
    }
    
    public boolean process(final Exchange exchange, final AsyncCallback callback) {
        boolean sync = false;
        List<Processor> list = getProcessors();
        if (list.isEmpty()) {
            throw new IllegalStateException("No processors available to process " + exchange);
        }
        Processor processor = chooseProcessor(list, exchange);
        if (processor == null) {
            throw new IllegalStateException("No processors could be chosen to process " + exchange);
        } else {
            if (processor instanceof AsyncProcessor) {
                AsyncProcessor asyncProcessor = (AsyncProcessor)processor;
                sync = asyncProcessor.process(exchange, new AsyncCallback() {
                    public void done(boolean sync) {
                        // Only handle the async case...
                        if (sync) {
                            return;
                        } else {
                            callback.done(sync);                        
                        }
                    }
                });                
            } else {
                try {
                    processor.process(exchange);
                } catch (Exception ex) {
                    exchange.setException(ex);
                }
                callback.done(false);                
            }            
        }
        return sync;
        
    }

    protected abstract Processor chooseProcessor(List<Processor> processors, Exchange exchange);
}
