/*
    * Copyright 2006-2012 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.support.transaction;
  
  import java.io.IOException;
  import java.io.Writer;
  import java.nio.ByteBuffer;
  import java.nio.channels.FileChannel;
  
  import org.springframework.transaction.support.TransactionSynchronizationAdapter;
  import org.springframework.transaction.support.TransactionSynchronizationManager;
  
  /**
   * Wrapper for a {@link FileChannel} that delays actually writing to or closing the
   * buffer if a transaction is active. If a transaction is detected on the call
   * to {@link #write(String)} the parameter is buffered and passed on to the
   * underlying writer only when the transaction is committed.
   * 
   * @author Dave Syer
   * @author Michael Minella
   * 
   */
  public class TransactionAwareBufferedWriter extends Writer {
  
  	private static final String BUFFER_KEY_PREFIX = TransactionAwareBufferedWriter.class.getName() + ".BUFFER_KEY";
  
  	private static final String CLOSE_KEY_PREFIX = TransactionAwareBufferedWriter.class.getName() + ".CLOSE_KEY";
  
  	private final String bufferKey;
  
  	private final String closeKey;
  
  	private FileChannel channel;
  
  	private final Runnable closeCallback;
  	
  	// default encoding for writing to output files - set to UTF-8.
  	private static final String DEFAULT_CHARSET = "UTF-8";
  	
  	private String encoding = DEFAULT_CHARSET;
  	
  	/**
  	 * Create a new instance with the underlying file channel provided, and a callback
  	 * to execute on close. The callback should clean up related resources like
  	 * output streams or channels.
  	 * 
  	 * @param channel channel used to do the actuall file IO
  	 * @param closeCallback callback to execute on close
  	 */
  	public TransactionAwareBufferedWriter(FileChannel channel, Runnable closeCallback) {
  		super();
  		this.channel = channel;
  		this.closeCallback = closeCallback;
  		this.bufferKey = BUFFER_KEY_PREFIX + "." + hashCode();
  		this.closeKey = CLOSE_KEY_PREFIX + "." + hashCode();
  	}
  
  	public void setEncoding(String encoding) {
  		this.encoding = encoding;
  	}
  
  	/**
  	 * @return
  	 */
  	private StringBuffer getCurrentBuffer() {
  
  		if (!TransactionSynchronizationManager.hasResource(bufferKey)) {
  
  			TransactionSynchronizationManager.bindResource(bufferKey, new StringBuffer());
  
  			TransactionSynchronizationManager.registerSynchronization(new TransactionSynchronizationAdapter() {
  				@Override
  				public void afterCompletion(int status) {
  					clear();
  				}
  				
  				@Override
  				public void beforeCommit(boolean readOnly) {
  					try {
  						if(!readOnly) {
  							complete();
  						}
  					}
  					catch (IOException e) {
  						throw new FlushFailedException("Could not write to output buffer", e);
  					}
 				}
 
 				private void complete() throws IOException {
 					StringBuffer buffer = (StringBuffer) TransactionSynchronizationManager.getResource(bufferKey);
 					if (buffer != null) {
 						String string = buffer.toString();
 						byte[] bytes = string.getBytes(encoding);
 						int bufferLength = bytes.length;
 						ByteBuffer bb = ByteBuffer.wrap(bytes);
 						int bytesWritten = channel.write(bb);
 						if(bytesWritten != bufferLength) {
 							throw new IOException("All bytes to be written were not successfully written");
 						}
 						if (TransactionSynchronizationManager.hasResource(closeKey)) {
 							closeCallback.run();
 						}
 					}
 				}
 
 				private void clear() {
 					if (TransactionSynchronizationManager.hasResource(bufferKey)) {
 						TransactionSynchronizationManager.unbindResource(bufferKey);
 					}
 					if (TransactionSynchronizationManager.hasResource(closeKey)) {
 						TransactionSynchronizationManager.unbindResource(closeKey);
 					}
 				}
 
 			});
 
 		}
 
 		return (StringBuffer) TransactionSynchronizationManager.getResource(bufferKey);
 
 	}
 
 	/**
 	 * Convenience method for clients to determine if there is any unflushed
 	 * data.
 	 * 
 	 * @return the current size of unflushed buffered data
 	 */
 	public long getBufferSize() {
 		if (!transactionActive()) {
 			return 0L;
 		}
 		return getCurrentBuffer().length();
 	}
 
 	/**
 	 * @return
 	 */
 	private boolean transactionActive() {
 		return TransactionSynchronizationManager.isActualTransactionActive();
 	}
 
 	/*
 	 * (non-Javadoc)
 	 * 
 	 * @see java.io.Writer#close()
 	 */
 	@Override
 	public void close() throws IOException {
 		if (transactionActive()) {
 			if (getCurrentBuffer().length() > 0) {
 				TransactionSynchronizationManager.bindResource(closeKey, Boolean.TRUE);
 			}
 			return;
 		}
 		closeCallback.run();
 	}
 
 	/*
 	 * (non-Javadoc)
 	 * 
 	 * @see java.io.Writer#flush()
 	 */
 	@Override
 	public void flush() throws IOException {
 		if (!transactionActive()) {
 			channel.force(false);
 		}
 	}
 
 	/*
 	 * (non-Javadoc)
 	 * 
 	 * @see java.io.Writer#write(char[], int, int)
 	 */
 	@Override
 	public void write(char[] cbuf, int off, int len) throws IOException {
 
 		if (!transactionActive()) {
 			char [] subArray = new char[len];
 			System.arraycopy(cbuf, off, subArray, 0, len);
 			byte[] bytes = new String(subArray).getBytes(encoding);
 			int length = bytes.length;
 			ByteBuffer bb = ByteBuffer.wrap(bytes);
 			int bytesWritten = channel.write(bb);
 			if(bytesWritten != length) {
 				throw new IOException("Unable to write all data.  Bytes to write: " + len + ".  Bytes written: " + bytesWritten);
 			}
 			return;
 		}
 
 		StringBuffer buffer = getCurrentBuffer();
 		buffer.append(cbuf, off, len);
 	}
 }