/*******************************************************************************
 * Copyright (c) 2004 Actuate Corporation.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *  Actuate Corporation  - initial API and implementation
 *******************************************************************************/
package org.eclipse.birt.data.engine.executor.cache.disk;

import java.io.File;
import java.io.IOException;

import org.eclipse.birt.data.engine.executor.cache.ResultObjectUtil;
import org.eclipse.birt.data.engine.impl.StopSign;
import org.eclipse.birt.data.engine.odi.IResultObject;

/**
 * Provide the service of reading/writing objects for DiskMergeSort. As for
 * DiskMergeSort, it only needs to know which position of data is to read and to
 * be written, this class will convert such a request to reading/writing objects
 * from/to acutal file. It makes the reading/writing objects transparent to
 * DiskMergeSort.
 */
class SortDataProvider
{	
	// data count of one unit
	private int dataCountOfUnit;
		
	// temp file
	private File tempDir;
	private File goalFile;
	
	// data file reader/writer
	private DataFileReader dfrArray[];
	private DataFileWriter dfw;

	// cache data
	private IResultObject[][] cachedResultObjects;
	private int[] indexOfCachedRowData;
		
	// temp file prefix
	private String tempDirStr;
	private final static String tempFilePrefix = "data";

	// sort hint
	public final static int SORT_ITSELF = 0;
	public final static int SORT_MERGE = 1;
	
	// 
	private ResultObjectUtil resultObjectUtil;
	
	/**
	 * Construction
	 * 
	 * @param dataCountOfUnit
	 * @param tempDirStr
	 * @param goalFileStr
	 */
	SortDataProvider( int dataCountOfUnit, String tempDirStr,
			String goalFileStr, ResultObjectUtil resultObjectUtil )
	{
		this.dataCountOfUnit = dataCountOfUnit;
		this.resultObjectUtil = resultObjectUtil;

		tempDir = new File( tempDirStr );
		if ( tempDir.exists( ) == false )
			tempDir.mkdirs( );
		this.tempDirStr = tempDirStr;

		goalFile = new File( goalFileStr );
	}
	
	/**
	 * Initialize class members value, this function must be called
	 * 
	 * @param countOfUnit
	 */
	 void initForMerge( int dataCountOfTotal )
	{
		int countOfUnit = dataCountOfTotal / dataCountOfUnit;
		if ( dataCountOfTotal % dataCountOfUnit != 0 )
			countOfUnit++;

		dfrArray = new DataFileReader[countOfUnit];

		cachedResultObjects = new IResultObject[countOfUnit][];
		indexOfCachedRowData = new int[countOfUnit];
		for ( int i = 0; i < countOfUnit; i++ )
			indexOfCachedRowData[i] = -1;
	}

	/**
	 * Read specified position objects. One point needs to be noticed that in
	 * current algorithm implemenation, the data is read sequentially and then
	 * next begin will only have two possible values, 
	 * 1:in the scope of last [begin, end) 
	 * 2:(last end) +1.
	 * 
	 * @param begin
	 * @param end
	 * @param stopSign
	 * @return ResultObject[]
	 * @throws IOException, file reader exception
	 */
	IResultObject[] readData( int begin, int end, StopSign stopSign ) throws IOException
	{
		if ( begin == end )
			return new IResultObject[0];

		// get file reader
		int readerIndex = begin / dataCountOfUnit;
		if ( indexOfCachedRowData[readerIndex] == -1 )
		{
			File file = getTempFile( readerIndex );
			if ( dfrArray[readerIndex] == null )
				dfrArray[readerIndex] = DataFileReader.newInstance( file, resultObjectUtil );
			else
				dfrArray[readerIndex].setReadFile( file );
		}

		int length = end - begin;
		IResultObject[] sortedData = null;

		int offsetOfBegin = begin - indexOfCachedRowData[readerIndex];
		int cacheLength = cachedResultObjects[readerIndex] != null
				? cachedResultObjects[readerIndex].length : 0;
		if ( indexOfCachedRowData[readerIndex] == -1
				|| offsetOfBegin >= cacheLength )
		{
			// no any loaded data
			cachedResultObjects[readerIndex] = dfrArray[readerIndex].read( length, stopSign );
			sortedData = cachedResultObjects[readerIndex];
			indexOfCachedRowData[readerIndex] = begin;
		}
		else
		{
			int offsetOfEnd = end - indexOfCachedRowData[readerIndex];
			if ( offsetOfEnd > cacheLength )
			{
				// some data is loaded, but others is not
				IResultObject[] tempCachedData = new IResultObject[length];
				int fromBeginCachedLength = indexOfCachedRowData[readerIndex]
						+ cacheLength - begin;
				for ( int i = 0; i < fromBeginCachedLength; i++ )
					tempCachedData[i] = cachedResultObjects[readerIndex][offsetOfBegin
							+ i];

				int nextReadLength = offsetOfEnd - cacheLength;
				IResultObject[] nextSortData = dfrArray[readerIndex].read( nextReadLength, stopSign );
				for ( int i = 0; i < nextReadLength; i++ )
					tempCachedData[fromBeginCachedLength + i] = nextSortData[i];

				cachedResultObjects[readerIndex] = tempCachedData;
				indexOfCachedRowData[readerIndex] = begin;
				offsetOfBegin = begin - indexOfCachedRowData[readerIndex];
			}

			// get data from cache
			sortedData = new IResultObject[length];
			for ( int i = 0; i < length; i++ )
				sortedData[i] = cachedResultObjects[readerIndex][offsetOfBegin + i];
		}

		return sortedData;
	}

	/**
	 * Write specified position objects. One point needs to be noticed that in
	 * current algorithm implemenation, the data is written sequentially and
	 * then currPos value only has one possible values, that is the
	 * (currPos+length) of latest calling..
	 * 
	 * @param hint,
	 *            soring itself/merge sorting
	 * @param currPos,
	 *            current result object position
	 * @param resultObjects,
	 *            the result objects array needs to be written
	 * @param count
	 *            how many data of array will be written
	 * @param stopSign
	 * @throws IOException, file writer exception
	 */
	void writeData( int hint, int currPos, IResultObject[] resultObjects,
			int count, StopSign stopSign ) throws IOException
	{
		if ( hint == SortDataProvider.SORT_ITSELF )
		{
			int writerIndex = currPos / dataCountOfUnit;
			File outputFile = getTempFile( writerIndex );
			if ( dfw == null )
				dfw = DataFileWriter.newInstance( outputFile, resultObjectUtil );
			else if ( currPos % dataCountOfUnit == 0 )
				dfw.setWriteFile( outputFile );

			dfw.write( resultObjects, count, stopSign );
			dfw.close( );
		}
		else
		{
			if ( currPos == 0 )
				dfw.setWriteFile( goalFile );

			dfw.write( resultObjects, count, stopSign );
		}
	}

	/**
	 * end event, and thnen this class can do clean up task.
	 */
	void end( )
	{
		try
		{
			for ( int i = 0; i < dfrArray.length; i++ )
			{
				dfrArray[i].close( );
				File tempFile = getTempFile( i );
				tempFile.delete( );
			}
			tempDir.delete( );
			dfw.close( );
		}
		catch ( Exception e )
		{
			// ignore it
		}

		tempDir = null;
		goalFile = null;

		dfrArray = null;
		dfw = null;

		indexOfCachedRowData = null;
		cachedResultObjects = null;
	}
	
	/**
	 * Get temp file for external sorting, template file is automatic generated
	 * according to passed result object index value.
	 * 
	 * @param index
	 * @return temp file
	 * @throws IOException
	 */
	private File getTempFile( int index )
	{
		return new File( tempDirStr, tempFilePrefix + "_" + index );
	}

}