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/*******************************************************************************
 *
 *    Copyright (C) 2015-2018 the BBoxDB project
 *  
 *    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.bboxdb.storage.wal;

import java.io.BufferedInputStream;
import java.io.Closeable;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.util.Arrays;
import java.util.Iterator;

import org.bboxdb.storage.StorageManagerException;
import org.bboxdb.storage.entity.Tuple;
import org.bboxdb.storage.sstable.SSTableConst;
import org.bboxdb.storage.util.TupleHelper;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class WriteAheadLogReader implements Closeable, Iterable {
	
	/**
	 * The input stream
	 */
	private BufferedInputStream inputStream;

	/** 
	 * The file
	 */
	private final File file;

	/**
	 * The Logger
	 */
	private static final Logger logger = LoggerFactory.getLogger(WriteAheadLogReader.class);
	
	/** 
	 * The tuple iterator
	 */
	private final class TupleIterator implements Iterator {
		
		/**
		 * The next tuple
		 */
		private Tuple nextTuple = null;
		
		@Override
		public boolean hasNext() {
			
			// We have already fetched a tuple
			if(nextTuple != null) {
				return true;
			}
			
			try {
				final int availableBytes = inputStream.available();
				
				if(availableBytes == 0) {
					return false;
				}
				
				nextTuple = TupleHelper.decodeTuple(inputStream);
				
				return true;
			} catch (IOException e) {
				logger.error("Got IO exception", e);
				return false;
			}
		}

		@Override
		public Tuple next() {
			
			if(nextTuple == null) {
				throw new RuntimeException("next() called but nextTupe is null,"
						+ " do you forget to call hasNext()?");
			}
			
			final Tuple tupleToReturn = nextTuple;
			nextTuple = null;
			return tupleToReturn;
		}
	}
	
	public WriteAheadLogReader(final File basedir, final int memtableNumber) throws IOException, StorageManagerException {
		this(WriteAheadLogManager.getFileForWal(basedir, memtableNumber));
	}
	
	public WriteAheadLogReader(final File file) throws IOException, StorageManagerException {
		
		if(! file.exists()) {
			throw new IOException("File " + file + " does not exist");
		}
		
		this.file = file;
		this.inputStream = new BufferedInputStream(new FileInputStream(file));
				
		// Validate file - read the magic from the beginning
		final byte[] expectedMagic = SSTableConst.MAGIC_BYTES_WAL;
		final byte[] magicBytes = new byte[expectedMagic.length];
		
		inputStream.read(magicBytes, 0, expectedMagic.length);

		if(! Arrays.equals(magicBytes, expectedMagic)) {
			throw new StorageManagerException("File " + file + " does not contain the magic bytes");
		}
	}

	/**
	 * Close the WAL reader
	 */
	@Override
	public void close() throws IOException {
		if(inputStream != null) {
			inputStream.close();
			inputStream = null;
		}
	}

	@Override
	public Iterator iterator() {
		return new TupleIterator();
	}
	
	/**
	 * Delete the base file
	 * @throws IOException
	 */
	public void deleteFile() throws IOException {
		close();
		
		if(file.exists()) {
			file.delete();
		}
	}
}