/*
** Authored by Timothy Gerard Endres
** <mailto:time@gjt.org>  <http://www.trustice.com>
** 
** This work has been placed into the public domain.
** You may use this work in any way and for any purpose you wish.
**
** THIS SOFTWARE IS PROVIDED AS-IS WITHOUT WARRANTY OF ANY KIND,
** NOT EVEN THE IMPLIED WARRANTY OF MERCHANTABILITY. THE AUTHOR
** OF THIS SOFTWARE, ASSUMES _NO_ RESPONSIBILITY FOR ANY
** CONSEQUENCE RESULTING FROM THE USE, MODIFICATION, OR
** REDISTRIBUTION OF THIS SOFTWARE. 
** 
*/

package edu.uoregon.tau.common.tar;

import java.io.*;


/**
 * The TarBuffer class implements the tar archive concept
 * of a buffered input stream. This concept goes back to the
 * days of blocked tape drives and special io devices. In the
 * Java universe, the only real function that this class
 * performs is to ensure that files have the correct "block"
 * size, or other tars will complain.
 * <p>
 * You should never have a need to access this class directly.
 * TarBuffers are created by Tar IO Streams.
 *
 * @version $Revision: 1.1 $
 * @author Timothy Gerard Endres,
 *  <a href="mailto:time@gjt.org">time@trustice.com</a>.
 * @see TarArchive
 */

public
class		TarBuffer
extends		Object
	{
	public static final int		DEFAULT_RCDSIZE = ( 512 );
	public static final int		DEFAULT_BLKSIZE = ( DEFAULT_RCDSIZE * 20 );

	private InputStream		inStream;
	private OutputStream	outStream;

	private byte[]	blockBuffer;
	private int		currBlkIdx;
	private int		currRecIdx;
	private int		blockSize;
	private int		recordSize;
	private int		recsPerBlock;

	private boolean	debug;


	public
	TarBuffer( InputStream inStream )
		{
		this( inStream, TarBuffer.DEFAULT_BLKSIZE );
		}

	public
	TarBuffer( InputStream inStream, int blockSize )
		{
		this( inStream, blockSize, TarBuffer.DEFAULT_RCDSIZE );
		}

	public
	TarBuffer( InputStream inStream, int blockSize, int recordSize )
		{
		this.inStream = inStream;
		this.outStream = null;
		this.initialize( blockSize, recordSize );
		}

	public
	TarBuffer( OutputStream outStream )
		{
		this( outStream, TarBuffer.DEFAULT_BLKSIZE );
		}

	public
	TarBuffer( OutputStream outStream, int blockSize )
		{
		this( outStream, blockSize, TarBuffer.DEFAULT_RCDSIZE );
		}

	public
	TarBuffer( OutputStream outStream, int blockSize, int recordSize )
		{
		this.inStream = null;
		this.outStream = outStream;
		this.initialize( blockSize, recordSize );
		}

	/**
	 * Initialization common to all constructors.
	 */
	private void
	initialize( int blockSize, int recordSize )
		{
		this.debug = false;
		this.blockSize = blockSize;
		this.recordSize = recordSize;
		this.recsPerBlock = ( this.blockSize / this.recordSize );
		this.blockBuffer = new byte[ this.blockSize ];

		if ( this.inStream != null )
			{
			this.currBlkIdx = -1;
			this.currRecIdx = this.recsPerBlock;
			}
		else
			{
			this.currBlkIdx = 0;
			this.currRecIdx = 0;
			}
		}

	/**
	 * Get the TAR Buffer's block size. Blocks consist of multiple records.
	 */
	public int
	getBlockSize()
		{
		return this.blockSize;
		}

	/**
	 * Get the TAR Buffer's record size.
	 */
	public int
	getRecordSize()
		{
		return this.recordSize;
		}

	/**
	 * Set the debugging flag for the buffer.
	 *
	 * @param debug If true, print debugging output.
	 */
	public void
	setDebug( boolean debug )
		{
		this.debug = debug;
		}

	/**
	 * Determine if an archive record indicate End of Archive. End of
	 * archive is indicated by a record that consists entirely of null bytes.
	 *
	 * @param record The record data to check.
	 */
	public boolean
	isEOFRecord( byte[] record )
		{
		for ( int i = 0, sz = this.getRecordSize() ; i < sz ; ++i )
			if ( record[i] != 0 )
				return false;

		return true;
		}

	/**
	 * Skip over a record on the input stream.
	 */

	public void
	skipRecord()
		throws IOException
		{
		if ( this.debug )
			{
			System.err.println
				( "SkipRecord: recIdx = " + this.currRecIdx
					+ " blkIdx = " + this.currBlkIdx );
			}

		if ( this.inStream == null )
			throw new IOException
				( "reading (via skip) from an output buffer" );

		if ( this.currRecIdx >= this.recsPerBlock )
			{
			if ( ! this.readBlock() )
				return; // UNDONE
			}

		this.currRecIdx++;
		}

	/**
	 * Read a record from the input stream and return the data.
	 *
	 * @return The record data.
	 */

	public byte[]
	readRecord()
		throws IOException
		{
		if ( this.debug )
			{
			System.err.println
				( "ReadRecord: recIdx = " + this.currRecIdx
					+ " blkIdx = " + this.currBlkIdx );
			}

		if ( this.inStream == null )
			throw new IOException
				( "reading from an output buffer" );

		if ( this.currRecIdx >= this.recsPerBlock )
			{
			if ( ! this.readBlock() )
				return null;
			}

		byte[] result = new byte[ this.recordSize ];

		System.arraycopy(
			this.blockBuffer, (this.currRecIdx * this.recordSize),
			result, 0, this.recordSize );

		this.currRecIdx++;

		return result;
		}

	/**
	 * @return false if End-Of-File, else true
	 */

	private boolean
	readBlock()
		throws IOException
		{
		if ( this.debug )
			{
			System.err.println
				( "ReadBlock: blkIdx = " + this.currBlkIdx );
			}

		if ( this.inStream == null )
			throw new IOException
				( "reading from an output buffer" );

		this.currRecIdx = 0;

		int offset = 0;
		int bytesNeeded = this.blockSize;
		for ( ; bytesNeeded > 0 ; )
			{
			long numBytes =
				this.inStream.read
					( this.blockBuffer, offset, bytesNeeded );

			//
			// NOTE
			// We have fit EOF, and the block is not full!
			//
			// This is a broken archive. It does not follow the standard
			// blocking algorithm. However, because we are generous, and
			// it requires little effort, we will simply ignore the error
			// and continue as if the entire block were read. This does
			// not appear to break anything upstream. We used to return
			// false in this case.
			//
			// Thanks to 'Yohann.Roussel@alcatel.fr' for this fix.
			//

			if ( numBytes == -1 )
				break;

			offset += numBytes;
			bytesNeeded -= numBytes;
			if ( numBytes != this.blockSize )
				{
				if ( this.debug )
					{
					System.err.println
						( "ReadBlock: INCOMPLETE READ " + numBytes
							+ " of " + this.blockSize + " bytes read." );
					}
				}
			}

		this.currBlkIdx++;

		return true;
		}

	/**
	 * Get the current block number, zero based.
	 *
	 * @return The current zero based block number.
	 */
	public int
	getCurrentBlockNum()
		{
		return this.currBlkIdx;
		}

	/**
	 * Get the current record number, within the current block, zero based.
	 * Thus, current offset = (currentBlockNum * recsPerBlk) + currentRecNum.
	 *
	 * @return The current zero based record number.
	 */
	public int
	getCurrentRecordNum()
		{
		return this.currRecIdx - 1;
		}

	/**
	 * Write an archive record to the archive.
	 *
	 * @param record The record data to write to the archive.
	 */

	public void
	writeRecord( byte[] record )
		throws IOException
		{
		if ( this.debug )
			{
			System.err.println
				( "WriteRecord: recIdx = " + this.currRecIdx
					+ " blkIdx = " + this.currBlkIdx );
			}

		if ( this.outStream == null )
			throw new IOException
				( "writing to an input buffer" );

		if ( record.length != this.recordSize )
			throw new IOException
				( "record to write has length '" + record.length
					+ "' which is not the record size of '"
					+ this.recordSize + "'" );

		if ( this.currRecIdx >= this.recsPerBlock )
			{
			this.writeBlock();
			}

		System.arraycopy(
			record, 0,
			this.blockBuffer, (this.currRecIdx * this.recordSize),
			this.recordSize );

		this.currRecIdx++;
		}

	/**
	 * Write an archive record to the archive, where the record may be
	 * inside of a larger array buffer. The buffer must be "offset plus
	 * record size" long.
	 *
	 * @param buf The buffer containing the record data to write.
	 * @param offset The offset of the record data within buf.
	 */

	public void
	writeRecord( byte[] buf, int offset )
		throws IOException
		{
		if ( this.debug )
			{
			System.err.println
				( "WriteRecord: recIdx = " + this.currRecIdx
					+ " blkIdx = " + this.currBlkIdx );
			}

		if ( this.outStream == null )
			throw new IOException
				( "writing to an input buffer" );

		if ( (offset + this.recordSize) > buf.length )
			throw new IOException
				( "record has length '" + buf.length
					+ "' with offset '" + offset
					+ "' which is less than the record size of '"
					+ this.recordSize + "'" );

		if ( this.currRecIdx >= this.recsPerBlock )
			{
			this.writeBlock();
			}

		System.arraycopy(
			buf, offset,
			this.blockBuffer, (this.currRecIdx * this.recordSize),
			this.recordSize );

		this.currRecIdx++;
		}

	/**
	 * Write a TarBuffer block to the archive.
	 */
	private void
	writeBlock()
		throws IOException
		{
		if ( this.debug )
			{
			System.err.println
				( "WriteBlock: blkIdx = " + this.currBlkIdx );
			}

		if ( this.outStream == null )
			throw new IOException
				( "writing to an input buffer" );

		this.outStream.write( this.blockBuffer, 0, this.blockSize );
		this.outStream.flush();

		this.currRecIdx = 0;
		this.currBlkIdx++;
		}

	/**
	 * Flush the current data block if it has any data in it.
	 */

	private void
	flushBlock()
		throws IOException
		{
		if ( this.debug )
			{
			System.err.println( "TarBuffer.flushBlock() called." );
			}

		if ( this.outStream == null )
			throw new IOException
				( "writing to an input buffer" );

		// Thanks to 'Todd Kofford <tkofford@bigfoot.com>' for this patch.
		// Use a buffer initialized with 0s to initialize everything in the
		// blockBuffer after the last current, complete record. This prevents
		// any previous data that might have previously existed in the
		// blockBuffer from being written to the file.

		if ( this.currRecIdx > 0 )
			{
			int offset = this.currRecIdx * this.recordSize;
			byte[]	zeroBuffer = new byte[ this.blockSize - offset ];

			System.arraycopy
				( zeroBuffer, 0, this.blockBuffer, offset, zeroBuffer.length );

			this.writeBlock();
			}
		}

	/**
	 * Close the TarBuffer. If this is an output buffer, also flush the
	 * current block before closing.
	 */
	public void
	close()
		throws IOException
		{
		if ( this.debug )
			{
			System.err.println( "TarBuffer.closeBuffer()." );
			}

		if ( this.outStream != null )
			{
			this.flushBlock();

			if ( this.outStream != System.out
					&& this.outStream != System.err )
				{
				this.outStream.close();
				this.outStream = null;
				}
			}
		else if ( this.inStream != null )
			{
			if ( this.inStream != System.in )
				{
				this.inStream.close();
				this.inStream = null;
				}
			}
		}

	}

