/*
 * Copyright 2006-2013 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.springframework.batch.core.scope.context;

import java.util.Queue;
import java.util.concurrent.LinkedBlockingQueue;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.batch.core.Step;
import org.springframework.batch.core.StepExecution;
import org.springframework.batch.repeat.RepeatCallback;
import org.springframework.batch.repeat.RepeatContext;
import org.springframework.batch.repeat.RepeatStatus;
import org.springframework.util.ObjectUtils;

/**
 * Convenient base class for clients who need to do something in a repeat
 * callback inside a {@link Step}.
 *
 * @author Dave Syer
 *
 */
public abstract class StepContextRepeatCallback implements RepeatCallback {

	private final Queue<ChunkContext> attributeQueue = new LinkedBlockingQueue<ChunkContext>();

	private final StepExecution stepExecution;

	private final Log logger = LogFactory.getLog(StepContextRepeatCallback.class);

	/**
	 * @param stepExecution
	 */
	public StepContextRepeatCallback(StepExecution stepExecution) {
		this.stepExecution = stepExecution;
	}

	/**
	 * Manage the {@link StepContext} lifecycle. Business processing should be
	 * delegated to {@link #doInChunkContext(RepeatContext, ChunkContext)}. This
	 * is to ensure that the current thread has a reference to the context, even
	 * if the callback is executed in a pooled thread. Handles the registration
	 * and unregistration of the step context, so clients should not duplicate
	 * those calls.
	 *
	 * @see RepeatCallback#doInIteration(RepeatContext)
	 */
	@Override
	public RepeatStatus doInIteration(RepeatContext context) throws Exception {

		// The StepContext has to be the same for all chunks,
		// otherwise step-scoped beans will be re-initialised for each chunk.
		StepContext stepContext = StepSynchronizationManager.register(stepExecution);
		if (logger.isDebugEnabled()) {
			logger.debug("Preparing chunk execution for StepContext: "+ObjectUtils.identityToString(stepContext));
		}

		ChunkContext chunkContext = attributeQueue.poll();
		if (chunkContext == null) {
			chunkContext = new ChunkContext(stepContext);
		}

		try {
			if (logger.isDebugEnabled()) {
				logger.debug("Chunk execution starting: queue size="+attributeQueue.size());
			}
			return doInChunkContext(context, chunkContext);
		}
		finally {
			// Still some stuff to do with the data in this chunk,
			// pass it back.
			if (!chunkContext.isComplete()) {
				attributeQueue.add(chunkContext);
			}
			StepSynchronizationManager.close();
		}
	}

	/**
	 * Do the work required for this chunk of the step. The {@link ChunkContext}
	 * provided is managed by the base class, so that if there is still work to
	 * do for the task in hand state can be stored here. In a multi-threaded
	 * client, the base class ensures that only one thread at a time can be
	 * working on each instance of {@link ChunkContext}. Workers should signal
	 * that they are finished with a context by removing all the attributes they
	 * have added. If a worker does not remove them another thread might see
	 * stale state.
	 *
	 * @param context the current {@link RepeatContext}
	 * @param chunkContext the chunk context in which to carry out the work
	 * @return the repeat status from the execution
	 * @throws Exception implementations can throw an exception if anything goes
	 * wrong
	 */
	public abstract RepeatStatus doInChunkContext(RepeatContext context, ChunkContext chunkContext) throws Exception;

}